Rice is the staple food of over half the world population. Rice is normally grown as an annual plant, although in tropical areas it can survive as a perennial crop and can produce a ratoon crop for up to 30 years. The rice plant can grow to 1 to 1.8 m tall, occasionally more depending on the variety and soil fertility. Since its origin, the spread of rice cultivation is extensive and rice is now being grown wherever water supply is adequate and ambient temperature are suitable. The rice grain is covered with a woody husk or hull, which is indigestible and is to be removed in the first step during processing for making the rice edible. Rice cultivation is well suited to countries and regions with low labor costs and high rainfall, as it is labor intensive to cultivate and requires ample water. Rice can be grown practically anywhere, even on a steep hill or mountain. The traditional method for cultivating rice is flooding the fields while, or after, setting the young seedlings. This simple method requires sound planning and servicing of the water damming and channeling, but reduces the growth of less robust weed and pest plants that have no submerged growth state, and deters vermin. While flooding is not mandatory for the cultivation of rice, all other methods of irrigation require higher effort in weed and pest control during growth periods and a different approach for fertilizing the soil. Drying is an essential step in the processing and preservation of paddy; it is the process that reduces grain moisture content to a safe level for storage. Milling is a crucial step in post production of rice. The basic objective of a rice milling system is to remove the husk and the bran layers, and produce an edible, white rice kernel that is sufficiently milled and free of impurities. India is the second largest rice producing country of the world after China. India also grows some of the finest quality aromatic rice of which basmati is the most high quality rice.
This book basically deals with history, origin and antiquity of rice, seed rice and seed production, harvest and post harvest operations, water management practices for rice, diseases and pests of rice and their control, application of biotechnology in aromatic rice improvement, traditional methods of parboiling, modernization of parboiling process, solvent extractive rice milling, general types of quick cooking rice processes, dry milled rice products in brewing, breakfast cereals, rice flakes, puffed rice, rice in multi grain cereals etc.
The present book contains cultivation and processing of rice in various ways. The book is very resourceful for the entrepreneurs, technocrats, research scholars etc.
HISTORY ORIGIN
and
Antiquity of Rice
The origin of rice (Oryza
sativa L.) has interested
some eminent botanists and
provisional
inferences were made in the first half of this century. A symposium was
held in
Delhi during 1950 on the origin of cultivated plants of South Asia and since then research on
the origin and
cytogenetics of rice has been intensified in India and in Japan.
Research
publications on the taxonomy evolution
and cytogenetics of rice and its relatives have appeared in many journ
als. A
recent review by Nayar gives a comprehensive bibliography and a
critical
discussion about Origin
and Cytogenetics
of Rice . Some supplementary information is given by Sampath and these
two
articles have to be consulted for details. It is here proposed to give
the
salient findings and to mention some of the topics on which further
studies are
needed.
ANTIQUITY
Formerly literary texts as well as
traditions were
cited to establish the antiquity of rice cultivation in a particular
region.
Because of difficulties in establishing the age of a particular text
and in
interpreting the statements pertaining to cereals
archaeological evidence is to be preferred.
Where rice grains chaff or husks are detectable in
pottery bricks or
mud constructions it
is possible to identify the material with
some confidence and to establish its age by dating with radiocarbon.
The first
detailed study of an archaeological rice sample from India was from
carbonized
grains excavated from Hastinapur north
of Delhi and was
dated as being between
1100 and 700 B.C. Subsequent archaeological evidence on rice in India
has been
reviewed by Buth and Saraswath. They consider the specimens collected
from
Atranjikera in Uttar Pradesh to be the oldest found so far and estimate
their
period of occurrence to range from 1500 1000 B.C. Vishnu Mittre has
given a
detailed discussion about the origin
antiquity and spread of rice cultivation in India. As
regards China another
ancient region of rice
cultivation pottery
excavated from Yang
Shao has been found to carry imprints as well as rice husks. The period
of that
culture is estimated at 2000 B.C.
but a
greater antiquity has also been claimed. The region covering Burma Thailand
and Cambodia is well suited to rice cultivation and has
also a large
population of wild rices. Therefore the discovery by a team of American
archaeologists of the most ancient finds of rice from excavations in
Thailand
is of interest. The work reviewed by Solheim suggests that these finds
reveal
the first agricultural beginning in southern Asia
important enough to be termed a revolution.
The specimens include horticultural plants as well as rice husks. The
dating
suggests that these specimens belong to the period ranging from 5000
4000 B.C.
This antiquity may be accepted provisionally and it may be inferred
that rice
cultivation spread to Vietnam
Taiwan China
as well as to India
from this centre. However an
independent
and parallel origin in Assam Bengal
and
Kerala cannot at
present be
dismissed.
SPECIES ANCESTRAL TO RICE
It has long
been
recognized that the wild species of Oryza
closely related to O. sativa
are
widely distributed in India Burma Thailand and Cambodia.
These wild populations
can be grouped into at least two taxa
but the distinctions are not clear cut
as intermediates have been arising as a result of natural
crossings. If
the division into taxa is to be made
it
is necessary to apply the rules of nomenclature and decide on the valid
names
of the two species. This is a controversial issue
as may be understood from the following
account. One taxon of restricted distribution is found on the margins
of
ponds is partly
floating and is
potentially perennial. This species is distinguished from its close
relative which is
seasonal having
slender grains and longer anthers
in addition to some differences in plant and
panicle characters. This species was used to be called Oryza perennis
(Moench).
This specific name is rejected as invalid by Tateoka in his
comprehensive
revision of the genus Oryza. A discussion about this and allied
taxonomic
difficulties is included in the book Rice Genetics and Cytogenetics. In
a
subsequent chapter of this monograph
details of taxonomy and species relationship are
elaborated. Since the
specific name perennis is widely used and is also convenient to
conserve as a
valid name Sampath
published an emended
description from a specimen collected in Orissa. It is
therefore
permissible to consider the Orissa type to be a subspecies
of a
widespread varying
and long anthered
wild rice. The other taxon has bolder grains
shorter anthers and generally stouter awns. This species
has large
populations and shows greater variation. Large populations of this
species can
be seen beside the railway track on
Borrow Pits along
the east coast
of India north of
Vijayawada and
including Bengal. These plants flower during October when their
conspicuous
pink awns make the specific name O. rufipogon Griffith. It is possible
that
this species evolved from hybrids
between O. sativa and O.
perennis. Moench emend. Sampath because
it has been repeatedly observed in many countries that where O.
perennis grows
adjacent to rice plots cross
pollination
from wild rice takes place. The extent of crossing is low but in the course of time
a weed population
builds up in the rice fields since
the
hybrid plants shed their seeds which
remain dormant till the next season. In the course of generations a
diversified
population can evolve from the hybrids
and can invade new habitats. It is also possible that the
very large
populations may be grouped together as a single species to include
genotypes which had
evolved from O.
perennis before
human intervention as
an adaptation to habitats liable to
drought.
A theory
has
been advanced that climatic changes during the Pleistocene Period
induced
physiological stresses in the herbaceous flora and the evolution of
seasonal
forms the existing perennial ones was accelerated. An exposition of
this
theory as
pertaining to the Gramineae of
Asia is made by
R.O. Whyte (in press).
To apply this concept to rice is to infer the changes as perennial
climatic
stress seasonal human selection cultivated rice. The term genome
which is explained later in this book has to be used for
supporting this
hypothesis. The symbol A is used for the genome
present in a species
at the diploid level in O. perennis
O.
rufipogon and also in O. sativa. The theory of evolution precludes the
separate
creation of a species. Therefore the species having the
A
genome are interrelated and their evolution may be
traceable. A
simplified statement of the ancestry of the cultivated rice is as
follows. The
perennial long anthered species is the ultimate ancestor but possibly
another
taxon with bolder grains and seasonal habit was the immediate ancestor.
For
details the review
of Nayar may be seen.
Under this topic there
is a need for
further research to arrive at a firm conclusion.
GENETIC PROCESS INVOLVED IN DOMESTICATION
For the
human
selection to operate there
must be
genetic variability present in populations
which must be responsive to the procedures of primitive
agriculturists.
The details of cultivation practices in ancient times cannot be traced
but it
can be inferred that in some areas
the
scrub or the jungle was cut burnt crudely leveled and the
seeds of crops were
sown. In river valleys and deltas
the
procedures would be slightly different
suggesting a more advanced agriculture. The method used by
primitive
agriculturists for harvesting and seed selection is not known. Initially the seeds of wild rice
must have been used.
The perennial wild rice is partly out crossing
hence heterozygous
and different
populations show differences in genetic composition. Hybridization
between
different genotypes followed
by
inbreeding would
lead to rapid changes
in plant characteristics. Mutations for nonshedding awnless grains
would be
intensively selected by the primitive agriculturists. Sampath has
suggested
that hybridity in the molecular structure of some key enzymes could
have played
a part in the evolution of O. sativa. Studies on population genetics of
the
wild rices of the world have been carried out by Dr H.I. Oka and his
collaborators at the National Institute of Genetics
Misima. These studies contribute
substantially to an understanding of the origin of O. sativa. Two of
his
collaborators gave experimental findings and summarized his
interpretation. In
a joint contribution the dynamics of plant domestication as applicable to rice is discussed. In view of
such significant
studies any further advance under this topic can come only as the
result of
combined cytogenetic and biochemical studies on hybrids and hybrid
progenies of
wild rices.
Breeding
Rice
breeding in
India started in 1911 in undivided Bengal
with the appointment of Dr G.P. Hector as Economic
Botanist with his
headquarters at Dacca which
is now in
Bangladesh. In 1912 Madras
province had
the first crop specialist fully devoted to rice. The period from 1911
1979 may
be considered under three distinct periods as far as rice breeding in
India is
concerned viz. of mainly pure line
selections and very few
hybridizations of inter racial hybridization between japonicas and
indices and of
inter racial hybridization with semi
dwarfs especially
Taiwanese indices.
Prior to
1930 Bengal and
Madras were the only
provinces which had
full time
specialists for the crop. When the Indian Council of Agricultural
Research was
established in 1929 it
initiated rice
research projects in many states which did not have a rice programme
and this
gave an impetus to the development of rice research in the country and by 1950
there were 82 research stations devoted to rice in 14
states of India.
These research stations released 445 improved varieties
mainly by the pure line method of selection.
Of course a few
(e.g. Co. 15
Co. 16
Co. 25
Co. 26
Co. 29
Co. 30 ) were hybrid
derivatives from indica crosses but
numerically they were insignificant when compared to those evolved
through pure
line selections. The number of varieties released from each state is
given
below.
Ramiah and
Rao
have delineated the development of Rice Research Stations in India. The
establishment of these different stations was prompted by the need to
cater for
different ecological conditions. Ghose et al. had listed the broad
breeding
objectives which made possible the development of 445 improved
varieties in the
country. They were (1)
Earliness (2) Deep
water and flood resistance (3)
Lodging resistance (4)
Drought resistance (5)
Non shedding of grains (6)
Dormancy of seed (7)
Control of wild rice (18)
Disease resistance and (9) Higher
response to heavy manuring.
Table
1. The number of varieties
released by different states through selection and hybridization
Thus the earlier breeding
efforts were directed
towards the development of varieties adapted to specific stress
situations or
for resistance to diseases prevalent in the region or what the Japanese
called ecological
breeding . When
synthetic fertilizers began to be popular after World War II efforts were made to
identify varieties which
respond to heavy manuring. There were no major pest problems and the
progress
though not spectacular did not pose possibilities of serious disaster.
Through
pure line selection the
advantages of
natural selections over centuries had been fully made use of and there
were no
problems of antagonism involved in the introduction of new genes to an
incompatible environment. The surviving genotypes seemed to be more
suited to
their environment underscoring the significance of survival and
adaptation in
evolution.
After the
establishment of the Central Rice Research Institute in 1946 at Cuttuck there had been a
systematic screening of
exotic types from the genetic stocks and many Chinese
Japanese
Taiwanese and Russian types were tested for the purpose of
direct
introduction in the country. The result showed that the early duration
local
varieties like Benibhog were superior to the
exotic introductions.
Notable among the Chinese introductions were
Ch. 4
Ch. 45
Ch. 55
Ch. 62 and Ch. 63
of these Ch.
45 proved to be a
good yielder combined with
earliness and Helminthosporium resistance and had been used as a donor
in some
of the modern varieties.
Prior to
1947 Chinese
varieties were first
introduced in Kashmir Valley possibly
due to reasons of geographical proximity or contiguity and have been
found
suitable and so extensively cultivated. The most notable of these
introductions
is Ch. 1039 which is the leading
variety of Kashmir
Valley even today. Others are Ch.
27 Ch.
47 Ch.
962
Ch. 971 and Ch. 972 .
Though the
Chinese types were fairly successful
the
Japanese and Russian introductions were found unsuitable under Indian
conditions mainly
because of their low
yield unacceptable
grain qualities and
susceptibility to blast.
Period of inter racial hybridization between japonicas and
indicas
The end of
the
Second World War and the subsequent population explosion stimulated the
Food
and Agricultural Organization of the United Nations to take up the
problem of
improving production of this major Asian and world cereal on an
international
basis and the result was a collaborative project of japonica × indica
hybridization in South East Asian countries. Japan had started using
chemical
fertilizers from the beginning of this century and so japonicas the cultivated rices of
Japan showed
response to fertilizer under Japanese
conditions up to 60 100 kg N/ha whereas
the indicas cultivated
types in
Asia responded to N
fertilizer only up
to 20 30 kg N/ha.
The
rationale of
the F.A.O. project was to transfer the high yielding ability and
response to
heavy fertilizer inputs that characterize the japonicas into the local
indica
varieties which
were adapted to their
respective conditions of culture and had tolerance to the prevalent
diseases
and pests of the region.
A parallel
scheme of japonica × indica hybridization was also drawn up by the
Indian
Council of Agricultural Research (ICAR) with the same objectives of
identifying
varieties with response to fertilizer and having the major features of
the
local varieties of the different states.
These two
projects used 192 improved indica varieties
selected by the participating Asian countries and Indian
states and
produced a total of 710 different japonica × indica hybrids. F1 seeds
of these
hybrids were distributed to the different participating countries or
states for
growing the F2 and subsequent generations in their respective regions
to breed
varieties suited to those agro climatic conditions.
These
projects could claim only
very limited success as only four varieties were released from the
seven
hundred and odd hybrid combinations.
Malinja and Mahsuri
in Malaysia
Adt. 27 in
Tamil Nadu state of India and Circna
in Australia were the varieties named.
Another
scheme
was lunched by Central Rice Research Institute (CRRI) in 1960 to evolve high yielding
fertilizer responsive hybrid varieties with japonica in 11
states. The
development of the semi dwarf varieties in Taiwan and Philippines and
their
introduction into India put an abrupt end to this scheme in 1966 even before the results
could be properly
assessed.
But in
another
later attempt at Central Rice Research Institute
Rao and Nagaraju achieved remarkable success
in the development of japonica×indica hybrids
fully achieving the objectives envisaged in the original
international
and national hybridization projects. Their success might be attributed
to the
choice of short statured japonicas (as against the tall ones previously
used)
grown in South Japan which
climatically
is fairly similar to Taiwan (and not from Hokkaido the coldest region where
rice is grown).
So varieties
adapted to mild temperate
region were seen to be more productive under tropical conditions than
those
from extremely cold temperate zone. This emphasises the importance of
selecting
suitable parents with adaptability in rice improvement/hybridization
programmes.
During the
period of japonica×indica hybridization
time and again it was stressed
that the japonicas had high yielding ability and response
to fertilizer.
But in India the
introduced japonicas
had been a total failure except
in the
hills and some cool areas. Japonicas were both photoperiod and
temperature
sensitive and so flowered in 35 40 days and did not get enough time for
proper
vegetative growth and tillering and so were not half as productive as
the
indicas under Indian conditions nor did they exhibit any of the virtues
for
which they were famous in Japan. Therefore
the limited success of the first two japonica × indica
hybridization
projects was natural as the very premise of the project of transferring
the
high yield potential and response to fertilizer of japonicas was not
apparent
in them under Indian conditions. Besides
the character of response to high
fertility is an
interaction of environment and genotype and when the environment was
changed
the interaction also gave different or negative results. The chances of
getting
hybrid recombinants with the desirable attributes of both the parents
from such
a wide genetic scrambling were a slender as getting highly productive
hybrids
as transgressive segregants from any other inter or intra racial
crosses
involving ordinary or poor yielding parents.
It was
obvious
that the short photoperiod and tropical conditions of the Indian plains transformed the entire
physiology of
growth development
and productivity of
japonicas which
therefore could not provide
productive recombinants in a Mendelian proportion. The ecological
specialization to divergent situations had caused genetic
incompatibility
between the races and the japonica × indica hybrids were seen to have a
very
high degree (even to 99%) of spikelet sterility in the segregating
populations.
This is an interesting instance of interaction between genotype and
environment
ruining the genetic potential for productivity in crop plants
themselves or in
their hybrid derivatives.
In Japan during the rice season the days are longer and
there is a higher
level of solar radiation that in tropical countries. In tropical region
of
India the day
length is fairly constant
during the crop season but
with low
solar radiation due to the overcast sky of the monsoon period. Where
the long
duration crops are raised though
the
days are bright there
is a shortening in
day length after
the autumn equinox contributing
to a reduction in the
availability of per day solar radiation. This is one of the significant
differences between the rice growing environments of tropical and
temperate
regions.
As
indicated
earlier CRRI has
been exploring the
possibility of direct introductions of exotic types from leading rice
producing
countries like Japan Taiwan etc. Some of the Japanese
varieties when
tried under 90 kg N and 35kg P2O5 per ha
were found promising (though on par or inferior to local varieties in
yield)
especially Norin 17 Norin
18
and Zuiho
. The Taiwanese
introduction Hsunchu was found not as productive as the local or
Japanese
types. The subsequent introduction of
intermediate types
from Taiwan
proved successful in many parts of the country like
Taichung 65
in Karnataka
Taichung (Native)
1 in Bihar Tainan 3
and Kaohsiung
18 in Kerala and
Hsunchu in
U.P. almost setting
the stage for the next phase
in Indian rice breeding.
Period of inter racial hybridization between semi dwarf
Taiwanese
types/derivatives and indicas
The
development
of Taichung
(Native) 1 from the
semidwarf mutant Dee geo woo gen was
major event in rice research in Asia and particularly for India T(N) 1
recorded a productivity which was considered impossible in
the tropics
before. It was felt then that
through
extensive cultivation of non lodging semidwarf hybrids
rice production could be substantially
increased in a short time as in wheat. Enunciation of the plant type
concept from an
elaboration of the
morphology in terms of the physiological efficiency of the semidwarfs stimulated breeding
activity throughout most
of South Asia and especially India which operated its most intensive
rice
breeding programmes since
1965 under the All
India Co ordinated Rice
Improvement Project (AICRIP). Initially
the aim was to identify semidwarf varieties that would
yield well from
Kanyakumari to Kashmir so
as to make the
seed multiplication and distribution system effective.
Padma
and Jaya were the first varieties
that emerged from
this programme. Subsequently varieties were released by Central Variety
Release
Committee and by
the different state
agencies. The list of released varieties is given in Appendix I. The
numerical
superiority of state releases stresses the importance of regional
adaptation in
rice varieties. Most of these varieties have a yield potential of 3 5
tonnes/ha.
The most
significant aspect of this period is the prolific release of hybrid
varieties.
During this phase 123
varieties were
released in twelve years compared
to the
51 hybrid varieties released during the four decades prior to 1965.
This surge
in hybrid releases was facilitated when semidwarf plant habit became
one of the
easily identifiable selection criteria for breeders.
The plant
type
or semidwarf varieties with the genetic architecture for physiological
efficiency of grain production have been found to be superior to the
tall
traditional varieties in both kharif and rabi seasons
but more so in the rabi season. The following
table illustrates the superior response of semidwarf varieties to
nitrogen
inputs for grain production in comparison to the traditional varieties
during
rabi season when the cultivation is under controlled irrigation and
ample solar
radiation.
As with
japonica
× indica hybridization the
inter racial
hybridization programme with Taiwanese varieties or derivatives also
ran into
difficulties. It was unfortunately reported in the early phase of the
semidwarf
period that through adoption of semidwarf varieties with improved
management
practices the
production problem could
be solved as was
done in wheat. But rice
being cultivated during the monsoon
when
no other cereal could be grown in heavy rainfall areas normally faced problems of
adaptation to specific
ecology and the newly introduced semidwarf types were found unsuitable
in a
variety of stress situations such
as
water logging salinity drought
low solar radiation due to clouded atmospheric condition etc. when these semidwarf
varieties were
cultivated under high fertility conditions
they were found susceptible to most of the pests and
diseases of rice.
Continuous and intensive cultivation of these semidwarfs caused disease
and
pest epidemics which
gave premonitions
of famine or ruin as in Bihar Andhra
Pradesh Kerala Indonesia and elsewhere.
These facts again
stress the importance of adaptability in monsoon rice varieties to the
tracts
in which they are to be grown. It is well known that monsoon fosters
most of
the pests and diseases of rice and high levels of fertilizer inputs
aggravate
their intensity. In such a situation
it
is unwise to advocate varieties of identical genetical constitution
over wide
tracts. Genetic diversity is still the best insurance against disease
and pest
epidemics as is illustrated by the Indonesian and Kerala catastrophes.
Table
2. Grain yields of
semidwarf and local types in kharif and rabi under different nitrogen
levels
The concern
with
disease and pest epidemics has intensified efforts for incorporation of multiple resistance by which is
meant resistance to more than
one disease or pest in
the varieties to
be developed. Many of the traditional indicas have been found to be the
major
donors for disease and pest resistance.
Thus having implicitly accepted
the production
superiority of the semidwarfs and widely popularized them we have to embark on
breeding plant type
varieties with tolerance to physiological stresses like
drought water
logging
saline tolerance cold
tolerance resistance
to diseases and
pests and good cooking and eating qualities
rather to transfer the desirable traits of the local
varieties to
the plant type background. The major
efforts made in these
directions are summarized below.
Breeding upland rices with tolerance to drought
In monsoon
dependent rice cultivation uplands
with
rainfall of 700 1100 mm get exposed to moisture stress periodically due to breaks in monsoon
lasting for
different periods of a week to ten days of erratic distribution of
rainfall.
Such areas constitute about a sixth of the world s rice acreage and
third of
the kharif rice area in India and it is necessary to stabilize yields
from such
lands to keep up the upward trend in rice production.
Uplands are
defined as those lands which are not bunded and wherein water is not
therefore
impounded during cultivation. Upland rice cultivation entirely depends
on
rainfall and it is a way of harvesting rain by adopting varieties of
suitable
duration according to the rainfall pattern.
Four
kinds of situations are possible
for such a kind of rice cultivation
Rains
adequate or assured during
vegetative and reproductive phases
Rains
inadequate or unreliable
during vegetative phase but adequate during reproductive phase
Rains
adequate during vegetative
phase but inadequate during reproductive phase
Rains
inadequate during both
vegetative and reproductive phase
The crux of
the
problem in upland breeding (exposed to moisture stress) as in items and is to find out
suitable donors with
drought tolerance during the vegetative and reproductive phases as
under
situation in item rice
cultivation is
not possible and in item there is no problem of moisture stress.
As there
are
uplands in all the rice growing states
many local varieties suited to such conditions have been
identified.
Through screening a
number of varieties
with varying degree of drought tolerance have been identified (e.g. Mtu. 17
Mettasannavari from
Andhra
Pradesh Ch.
45 from Bihar
Sathi 34 36 from
Gujarat Ptb.
28
Ptb. 29
Ptb. 30 from
Kerala
B 76 from
Orissa Lalnakanda
41 from Punjab
Tkm.l from
Tamil Nadu and N. 22
and Sudha from Uttar Pradesh.
Among
these it was found
that Lalnakanda 41 Ch. 45
and N.
22 have drought
tolerance at the vegetative
phase while Mtu. 17
showed drought tolerance even at the reproductive phase.
The first
attempt recorded to breed varieties with drought tolerance was in Tamil
Nadu
during the mid fifties and a drought tolerant variety
Co. 31
was released. Kerala also reported some drought tolerant
breeding lines
from the cross Krasnodar × Kattamodan
Culture No. 356 especially.
With the
introduction of Taichung
(Native) 1 during
1965
efforts were made to transfer drought tolerance to
semidwarf hybrids and
Bala from
the cross N. 22
× T
(N) 1 was the first
high yielding variety with
drought tolerance that was released in the country. As
Bala
was hard threshing efforts
were
made to identify lines with easy threshing and good grain qualities. CR. 113
CR. 115
CR. 141 and
CR. 143 had
many lines with
better threshability and grain qualities than
Bala . One line viz. CR. 141 192
from the cross (N. 22/ T(N) 1 × T. 90
IR. 8) had been named
Kiran in
Bihar. Hybrids more productive and
tolerant to drought than any of the parents had been identified in the
cross
CR. 125 (Lalnakanda 41 ×Mtu. 17) × T(N) 1.
International
Rice Research Institute (IRRI) geneticists have standardized the
testing
procedure for drought tolerance of upland rices and have made
considerable
progress by evolving a large number of promising cultures suited for
uplands.
Many of these are tested in most rice growing countries including India
through
the International Rice Testing Programme (IRTP). As the upland rice
problems
are faced by every rice growing state in India
a good number of cultures have been generated by states
using local
donors and at
present many are
under trial in the AICRIP testing
programme.
Efforts
were
also made at Central Rice Research Institute (CRRI) to evolve varieties
with
drought tolerance through induced mutation in traditional varieties.
Considerable success was achieved through this approach and many
mutants with
higher yield potential and drought tolerance than the parents had been
identified in Ch. 45 and
Mtu. 17 . Mutant Number 2 and 12 of
Mtu. 17 had
been in district
trials in Meghalaya and Manipur. Of special significance is Mtu. 17
Mutant No. 4 which
showed very
high tolerance to drought even during the flowering phase.
Another
mutant
from CR. 113 designated
CRM. 13 3241 is
possibly the
earliest induced productive major cereal in the world
maturing in seventy days when direct seeded
under a temperature regime of over 25°C. This mutant yields about 1½ 2
tonnes/ha normally but with good management has shown potential up to 5
tonnes/ha. In many State Farms under the Department of Agriculture of
Orissa
Government it had
recorded yields 2½ 3½
tonnes/ha. By relying on the earliness of this variety
known or predictable drought spells can be
avoided or there is a possibility to raise another rice crop after the
drought
or flood ravages and the resumption of normal monsoon. This variety is
to be
named shortly by the Orissa Department of Agriculture. In Assam it is found to be
promising as pre flood
kharif variety (March June) suited for direct seeded condition where it
could
be grown with the rains received during March June. In Tripura it has been found to be
useful in Tillo
lands (low mounds). This mutant is under extensive trial
in West Bengal.
Arunachal Pradesh and Madhya Pradesh.
Breeding for water logged and lowland conditions
Kharif is
the
main rice crop or season for India
extending from June to December
practically coinciding with the onset of the south west
monsoon and
complete recession of north east monsoon. Of the total 38.9 million
hectares
under rice in India about
20 million ha
or 50% of the area are under lowland where there is standing water of
varying
depths depending on the topography of the land for varying periods. The
lowlying areas can be classified into
Water
logged area (ill drained
conditions)
Flooded
areas and
Deep
water areas.
The water
logged
lowlands can be grouped into four categories depending on the depth of
standing
water and the
approximate area under
each according to the type of cultivation is shown in the following
table.
The above
classification is mainly based on the toposequence of rice fields. With
the
onset of monsoon medium
lands have
shallow rainfed conditions but water gets accumulated later at the peak
of
monsoon. So in the high rainfall zones
medium duration photosensitive varieties are grown in such
lands. Where
the rainfall is low photosensitive
varieties which
flower in 100 110
days are preferred.
The intermediate
lowlands constitute about half of the water logged areas and
photosensitive
varieties are grown in such lands. In the semi deep and deep water areas there is stagnation of
water with the onset
of heavy rains (normally from mid July onwards) and there is no way to
drain
off inundated water. Under such situations only broadcasting with the
onset of
monsoon is the usual practice.
Table
3. Distribution of water
logged areas according to type of cultivation and photosensitivity in
million
hectares
Soils Their
Classification and Agro Chemical Characteristics
The soils
on
which rice is grown are so extraordinarily varied that there is hardly
any type
of soil on which it cannot be grown with some degree of success. It is however
necessary that the deficiencies of the various soils are
identified and
made up to increase their productivity.
Classification and Distribution
The soils on which rice is grown in India and their
classification
The major
soil
groups producing rice are Riverine
alluvium red yellow red loamy
hill and submontane tarai laterite
coastal alluvium red
sandy or
gravelly patches of
mixed red and
black medium and
shallow black soils.
The
soils can generally be
classified for purposes of rice cultivation in India into
Alluvial
soils (Haplaquents Ustifluvents
Udifluvents Haplustalfs Ustochrepts)
Calcareous
alluvial soils
(Calciorthids)
Coastal
and deltaic alluvium
(Propsualfs)
Red
soils (Paleustalfs Rhodustalfs
Haplustalfs)
Red
and yellow soils
(Haplustults Ochraqults Rhodustalfs)
Lateritic
soils (Plinthaqults Plinthustults
Plinthudults Oxisols)
Black
soils (Ustochrepts Uatropepts
Pellusterts Chromusterts Pelluderts).
Mixed
red and black soils
(association of Alfisols and Vertisols)
Grey
brown soils (Calciorthids)
Brown
hill soils (Palchumults)
Submontane
soils (Hapludalfs)
Terai
soils (Haplaquolls)
Desert
soils (Lithic
Entisols Psamments Calciorthids)
Saline
alkali soils
(Salorthids Salargids
and
Natrargids) and
Peaty
and saline peaty soils
(Histosols).
Table
2. Ranges of moisture index
and the mean annual temperature in the various climatic zones as used by the Co
ordinated Agronomic
Experiments Scheme
Table
3. Characteristics of the
agroclimatic regions of India
For a
comprehensive and meaningful development of research programmes on a
regional
basis the Indian
Council of Agricultural
Research has identified eight agro climatic regions in the country and these regions also
represent the typical
rice growing regions of the country. The agro climatic regions
encompassing the
different states with soils
rainfall temperature etc.
which are significant from the point of view of rice
cultivation are
given in Table 1. This broad division into general agro climatic
regions is
suited for general agricultural purposes. The soils are also subdivided
into
agro climatic regions based on the degree of wetness
as measured by moisture index
which is the excess of precipitation over the
potential evapotranspiration expressed
as a percentage of the potential evapotranspiration divided into 8
classes designated
one to eight with
increasing wetness and with each one of
them again divided into subclasses
A B
C D and E
which are in an ascending order of coolness based on the mean average
temperature. The
ranges for the various classes are shown in Table 2. This classification as used by the Co
ordinated Agronomic
Experiments Scheme might
be very useful
for determining the cumulative effect of climate on soil characteristics but for its direct effect
on rice growth the
regions were divided into ten climatic
zones by Ghose Ghatge
and
Subrahmanyan not
only depending on the
rainfall but also
on the critical
temperature in the cold months the
duration of the dry periods relative
humidity etc. as described for the
individual states in the
last section of this chapter. The characteristics of these zones are
shown in
Table 3.
Distribution of various kinds of soils in India
The state
wise
area under rice is given in Table 4. The area occupied by rice in West
Bengal
and Bihar is nearly the same followed
by
Orissa Madhya
Pradesh Uttar
Pradesh
Andhra Pradesh Tamil
Nadu Assam
Maharashtra and Karnataka. These states put together account for more than 90
per cent of the
total rice producing area. They also constitute the traditionally rice
growing
areas in the country. The rest of the states have
however
limited areas under the rice crop.
The humid western Himalayan
region. This region
comprises submontane soils hill
soils
and terai soils in the states of Jammu and Kashmir
Himachal Pradesh and the Kumaon and Garhwal
divisions of Uttar Pradesh.
The soils
that
are found in the rice growing tract of Jammu and Kashmir are formed
from the
alluvium brought by the major rivers Chenab
Ravi Tawi
and their tributaries.
They occur mostly in the Jammu and Kathua districts. They vary in depth are light in texture and
their pH ranges from
6.5 to 8.7 they are
high in organic
matter nitrogen and
K2O but
are deficient in phosphorus.
The
submontane
soils include the valley floor and the karewa soils which occur in the
Anantnagh Baramulla
and Srinagar
districts. The valley floor has been constituted by the alluvium
deposited by
the Jhelum and the Indus. They are silty loam to clay loam and are
neutral to alkaline
(pH 5.4 8.5).
The karewa
soils
are somewhat eroded and formed from the deposits
which are of lacustrine nature. Their texture
is heavy their
contents of nitrogen and
organic matter are moderate to high
and
their total P and K ranges from 0.09 0.3 and 0.1 to 0.2 per cent
respectively.
The hill
soils
occur in Uttar Pradesh in the districts of Almora
Chamoli
Pithorgarh Uttar
Kashi and Dehra
Dun. They are shallow with fragments of rock occurring within a few
centimeters
at higher elevations but about three meters in valleys and lower
depressions.
They are derived from biotite schists and phyllitic materials under
moist
conditions. The soils groups described by Mukherji and Das fall under
the
categories of red loam brown
forest soil meadow
soil and podzolic soil.
The terai
soil
occurs as a narrow strip from the north west to the extreme north east.
The
soil remains saturated throughout the year because of sufficient
precipitation
and high ground water table. They have been formed from the transported
materials laid down by different rivers originating from the Himalayas.
They
are productive and respond to fertilizers. They are classified as
Molisols in
soil taxonomy.
In Himachal
Pradesh the hill
soils are formed over a
variety of parent rocks comprising sandstones
gray micaceous sandstones and shales in the sub Himalayan
region where
they are located. The soils are loam to silty loam and medium to high
in
organic matter total
nitrogen phosphorus
and potash. They are poor in
available nutrients. The cation exchange capacity is low to medium.
The humid
Bengal
Assam basin and the humid eastern Himalayan region and the Bay islands.
For
convenience these
two regions are dealt
with together. The altitude of the rice growing areas ranges from a few
metres
in Sundarbans in West Bengal to about 1660 metres in the north eastern
part of
the Himalayas in the Mizoram State and up to more than 2 000 metres in
Arunachal Pradesh.
The crop is
often grown on flat lands to facilitate the supply of water needs. It
is grown
successfully over a wide range of slopes
ranging from nearly level to very steep (podu or thum)
cultivation in
hilly areas. One of the main limiting factors is the availability of
water.
Owing to
the
adaptability of the rice crop to soils having a wide range of
characteristics it
is not possible to
categorize a particular soil group as rice soil or assess its best use
as rice
land.
The major
groups
of soils listed in the table for the two regions included riverine
alluvium the terai
soils red loamy
sandy or
gravelly red yellow
and laterite soils. Some of the
important soil series cultivated for rice in West Bengal extracted from
the
Soil Survey Reports are Canning
Kharbona Jagdishpur Sasanga
Hanrgra Totpara
and Banpara. They
are placed in Entisol Inceptisol
and
Alfisol in soil taxonomy.
The
alluvial
soils deposited by the rivers mostly occupy the major part of the
wetland rice
soils thus
contributing the largest
share to rice production in the country. They are derived from the
deposition mainly
as silt deposited by the numerous
tributaries of the Ganges and the Brahmaputra systems. The different
weathering
products of the Himalayas are deposited during the course of their flow
through
the plains.
In the
wetlands
the water table is high the
drainage is
poor and the entire profile remains in a reduced state. Mottled
horizons are
common and the accumulation of calcium carbonate in the lower horizons
is also
observed in soils. The flooded condition of paddy soils brings about
the
movement of iron and manganese compounds from the upper layers and
their
precipitation in the reduced zone of the lower horizon.
In West
Bengal
the Rarh
region which comprises portion of Murshidabad Bankura
the whole of Burdwan and the western half of Midnapore are
classified
under old alluvium. According to Mukerjee et al.
and Digar
the textures vary from sandy loams to heavy clays with a
hard pan.
The
laterite and
lateritic soils are found between the Damodar River and the Bhagirathi
River interspersed
with basaltic and
granitic hills. They may be classified into two groups. The first group
consists of soils of Midnapore
Bankura Burdwan
and Birbhum. In
these soils the
ratio of SiO2
Al2O3 is
quite high and
because of chemical weathering followed
by considerable leaching the
soils are
deficient in N P2O5
and K2O. They respond to N and P fertilization.
At some places buried
laterites are also observed at
considerable depths underlain by alluvium. These soils give better
response to
P2O5 and the yield of
rice is significantly increased by
the application of P2O5
rather than by that of N.
The red soils of Birbhum Bankura
Burdwan and West Dinajpur sometimes misclassified as
laterites are
transported from the hills of Chhotanagpur Plateau. They are acidic poor in Ca
N and available P. They are highly leached and respond to
N and P.
The coastal
soils in the districts of 24 Parganas and Midnapore after reclamation
are
producing good crop of rice. They are also rich in plant nutrients. The
terai
soils in the Jalpaiguri and Cooch Behar districts lying at the foot of
the
Himalayas are of raw humus type sandy
and gray to black.
Soils in
the
Assam Valley are acidic specially
the
old alluvial soils whereas
the new
alluvium is slightly acidic to neutral and
in some cases slightly
alkaline.
The soils are high in available P and K and moderate in organic matter
and
nitrogen.
The
lateritic
soils occur in the north eastern mountainous upland areas of Assam.
Drainage in
the uplands is good. The groundwater laterites are poorly drained. In
some
parts of West Bengal by
the augmentation
of irrigation sources from groundwater reserves through the sinking of
tube
wells rice is grown
in low medium and
upland situations. Though rice is
adapted to a wide range of soils as
mentioned earlier the
type of soils suitable
for it mainly depends upon the conditions under which the crop is grown
rather
than upon the nature of the soil.
By the
increase
in demands for more areas to be brought under the rice crop the conservation of
moisture during certain
periods becomes necessary owing to insufficient irrigation water.
Therefore
effective soil depth and suitable texture are very important.
In wetland
cultivation soil
structure is of little
significance but
good soil structure
ensures better water transmission and moisture preservation for the
dryland
crop.
The rice
crop is
better grown mostly in acidic soils whose pH ranges from 5.5 to 6.5. It
is
successfully grown in saline soils of Sudarabans in the Gangetic delta.
The sub humid Sutlej Ganga alluvial plains
This region
experiences low winter temperature and the usual practice are to take a
single
crop of rice between May June and September October.
The major
groups
of soil growing rice in the region are calcareous alluvial riverine alluvial saline alkaline red yellow loam red sandy or gravelly and
mixed red and
black. The alluvial soils owe their origin from the materials brought
and
deposited by the great rivers from the mountains. They are rich in
potash and
calcium but are
deficient in organic
matter nitrogen and
phosphorus. The
older alluvium is generally deficient in phosphorus
lime and organic matter
whereas the recent alluvium is well supplied
with nutrients because of fresh accumulation of river silt. The soils
are
placed in Entisol Inceptizon
and Alfisol
categories.
In the
irrigated
tracts of the Punjab state the
soils are
light textured and alkaline. Organic matter and nitrogen are low.
In Uttar
Pradesh the
alluvial soils occupy nearly
60 per cent of the area in the east
west south
and central parts of
the state. They have developed from the alluvium deposited by the Ganga
and the
Yamuna and their tributaries. The soils can be broadly classified under
(1)
light textured alluvium of the west and north west
(2) alluvium in the centre possessing intermediate
textures and (3)
alluvium in the north
east derived from the calcareous parent material.
Saline and
karail soils occur all along the Ganga river on the left side in the
districts
of Meerut Aligarh Bulandshar
Manipuri Etah Kanpur
Fatehpur Allahabad Lucknow
Pratapgarh and Sultanpur. The parent materials are
alluvial deposits in
the riverine areas and finely washed materials in the lower
depressions. The
soils are highly alkaline indurated
and
have hard pan which obstructs the downward movement of water.
The karail soils are black finer in texture and occur
in the lower basin
of Ganga. They occur in the districts of Allahabad
Varanasi
Ghazipur and Balia. They are formed from the black
alluvial deposits
transported by the Yamuna from central India.
The Ganga
divides Bihar into two halves north
and
south. The alluvium north of the Ganga has texture varying from sandy
loam to
clay loam and the pH is neutral to alkaline. Alkaline soils are
generally found
where the lime content is high. The alluvium south of the Ganga comprising the districts
of Patna Ganga and
parts of Shahabad is
gray to black and
light loam to heavy clay. Lime is less
and soil pH is slightly alkaline
changing to the acidic range in the southern extremity.
The middle part
which lies in a depression gets flooded during the monsoon. The
available K2O
and P2O5 are high.
The red
soils
occur in the districts of Ranchi
Hazaribagh Santal
Parganas Singhbhum
and Manbhum. They are acidic (pH 5.0 6.8) and contain
higher and soluble
Fe2O3 than Al2O3.
They are rich in
available K2O but are low in P2O5.
Seed Rice and Seed Production
The wide
use of
newly released varieties and proper seed production from breeder and
foundation
seed to the growers seed
stock on the
farm are essential for high level rice production with minimum input.
New and
superior varieties however can make their
contribution to practical
agriculture only if the seed reaches the farmer in varietally pure state in adequate quantities in an undamaged condition free of weed seed and at a reasonable price.
The general
purpose of seed production is to increase those old and new varieties which are superior to
standard varieties for
commercial distribution. The production of seed rice consists of
growing the
primary seed called
foundation seed and
then increasing this seed in sufficient
quantities to meet the request of the practical farmer for his seed
stock
supplies. To produce high quality seed
a
grower must have a superior seed source of a well adapted variety.
Formerly each farm
would obtain a
certain amount of such seed and multiply it to establish its own seed
stock on
the farm. But today modern
harvesting
and processing methods bulk
drying and
storage have increased the possibility of seed mixing. This led to the
need for
sources of pure seed. As a result
the
seed certification program now in effect in this county is an important
part of
rice production.
Sources of Pure Seed
Production
of
primary seed is carried out by institution for rice research and their
experimental stations and farms. They produce foundation seed (super
elite and
elite) and multiply promising varieties for release to the growers.
Production
of farm seed stock is done largely by the commercial grower who breeds
foundation
seed through three generations the
third
of which is sown for commercial grain output.
Classes of Seed
The
classes of seed termed
breeder foundation
and certified seed can
be described as follows.
Breeder
seed is seed directly
controlled by the plant breeding institution
and is the source of select seed handled at selected
nurseries for the
production of seed of the certified classes.
Foundation
seed is the progeny of
breeder or select seed handled at seed increase nurseries to maintain
specific
genetic purity and identity. Foundation seed is usually the first year
increase
from breeder seed. It is produced on fields that have not grown another
variety
or a lower class of the same variety during the 2 previous years. The
distribution of foundation seed to growers usually is handled through
specialized seed production farms and/or stations under a breeding
center that
increase this seed to the commercial growers as a certified class seed.
For new
varieties or for old varieties in short supply
specified amounts of seed may be increased or reduced
depending on
demand.
Certified
seed is the progeny of
breeder and more so
that foundation seed
is handled so as to maintain a satisfactory level of genetic purity and
identity. It is produced in riceland areas specifically allotted for
seed
increase purposes. The production and certification of seed is not a
part of
the breeding program.
The super
elite
and elite seed is distributed to growers to be increased to quantities
sufficient to maintain a seed stock necessary to satisfy the grower s
needs. Usually
the third year increase from certified or foundation seed is used for
commercial grain production. Thus
seed
of a commercially established variety is renewed once in three years.
For the production
of the various classes of certified seed it is necessary to have clean
land and
to prevent mixtures in seeding
harvesting and
processing. The
careful tending of all fields to remove undesirable weeds other crop and off type
plants may increase
the production costs but
is very
essential.
Seed Rice Culture
Varietally
pure high quality
seed in a viable
condition can be obtained only through the proper use of the whole
spectrum of
agronomic practices. This includes adequate seedbed preparation crops grown preparatory to
seeding rice the
use of high quality seed optimum
dates and methods of seeding adequate
fertilization and
finally proper mechanical treatments (threshing cleaning and grading).
Practical experience
has indicated that seed rice grown in good soil that receives the best
fertilization and cultivation treatments is usually larger in size than
seed of
the same variety grown in poor soil and inadequately cultivated. The
higher the
level of cultivation the
slower the
process of varietal deterioration under commercial farming. Strict
observance
of the seed production cultivation requirements usually results in seed
with
high varietal and field qualities which will be preserved well in the
5th or even 6th
generation. Any retreat from the established seed rice
cultural
requirements may bring about a rapid deterioration in the quality of
even the
first year seed. This will undoubtedly reduce the grain output of table
rice in
the area.
Usually the fields where rice will
be grown for seed
are treated much better than the commercial rice paddies to benefit the
rice
grower with seed rice of high standard. To avoid mixing
each variety is sown with a separate clean
seeder. The results of rice research and advanced practice indicate
that perennial
grasses cultivated
fallows and new
lands developed for rice are good for
seed rice production. The land should be thoroughly worked to a fine
tilth and
adequately fertilized. Saline lands are considered inadequate for seed
production and should be avoided. The irrigation and drainage
facilities should
be operable and in good shape and
the
land levelled to allow rapid flooding and draining if necessary.
The best
time to
sow rice for seed is when the soil temperature at a depth of 3 5 cm is
14 to
16°C which for most
rice growing areas
occurs in late April and early May.
To
obtain a high germination rate
the seed usually kept cooled during storage in the winter period is aerated and warmed up
either in grain bins
or grain driers and
treated with
granosan M 2 3 weeks before seeding.
The rate of
seeding depends on the variety and may vary from 4.5 million to 6
million
viable seeds per hectare. Where the elite seed is being increased for
commercial release the
rate of seeding
is reduced to 4 5 million viable seeds per hectare. Good results can be
obtained by drilling 3 million viable seeds per hectare in rows spaced
at 30
cm. This method has proved effective for rapid multiplication of new
and
promising varieties since under such a wide row method of seeding the
multiplication coefficient increases enabling the grower to achieve
higher
yields at a much lower rate of seeding. Under this method a rate of 100 kg viable
seeds per hectare
gave 7.16 t/ha of seed rice according to the USSR RRI data.
The wide
row
method of sowing rice for seed provides for a uniform ripening of seeds
on the
main and lateral panicles improves
plant
resistance to lodging and increases the productivity of the plant
stand. All
this in turn reduces the risk of blast disease and produces seed of a
higher
class. In addition this
method allows
for easy weeding to maintain varietal purity and identity of seed by
removing
off type and other crop plants from the field.
The time to
sow
rice for seed is equally important. Early seeding results in a thinned
stand
establishment during emergence while
with delayed seeding the seed usually fails to fully mature and as a result
exhibits poorer germination.
Seed rice
plantings require optimum levels of nutrients
particularly phosphorus. Excessive applications of
nitrogen fertilizers
should be avoided because high nitrogen contents delays maturity especially when the
weather during the
growing period is cool and rainy. In addition high nitrogen weakens the
strength of the stem of the rice plant
which leads to severe lodging
which results in poorly filled grain
high spikelet sterility
problems
at harvest time and
germination in the
panicle.
Insofar as
possible seed
fields should be managed
so as to minimize lodging and produce satisfactory yields without
excessive
vegetation growth. This is impossible with high single rates of nitrogen which must be applied in
divided or split
dressings. In seed fields ammonium sulfate and urea are preferred over
all
other sources of nitrogen.
Phosphorus
fertilizers appear to improve seed quality. Depending on the forecrop
and
degree of soil salinity phosphorus
is
applied as basal at rates from 90 to 150 kg P2O5 per hectare before
seeding.
Potash is also essential for seed fields to facilitate maturity obtain well filled grain and reduce the percentage
of empty spikelets.
Potassium is usually applied as topdressing during leaf tube formation
(the 8 9
leaf stage) at 30 to 60 kg K2O per hectare.
The Control of Red Rice
The
uses of specific varieties
that differ in maturity grain
type processing and
cooking qualities of rice
grain have increased the possibility of seed mixing. In this respect the production of seed
that is varietally
pure and free of persistent weed seeds become extremely important.
Preventing
intermixing throughout the various phases of seed production requires
very
close attention by the grower. Commercial varieties could become badly
mixed
with other varieties and infested with weedy strains of rice. These
strains are
the red rices that reduced grain and milled yield during harvesting and
processing.
All the
strains
of red rice are characterized by severe shattering
rapid growth
high yield and
a tolerance to
adverse environments. Red rice produces many tillers (up to 60) and the progeny from one
seed may amount to
1500 1600 viable seeds. Usually the
grower inadvertently spreads red rice by planting contaminated seed.
Because
herbicides do not selectively control red rice in the rice crop infestations should be
removed from seed rice
fields by other methods if one is to avoid deteriorated quality in seed
rice
and prevent further spreading of the weed. Red rice contaminates not
only the
seeding material but also the soil. Tests have indicated that without
proper
weeding the
quantity of red rice in the
seeding material the following season increases 5 to 10 fold.
To control
red
rice it is necessary to know the biology of its strains. Control is
difficult
yet possible through crop rotations
weeding operations renewal
of seed
sources adequate
tillage etc. Red
rice infestations of soil can be
prevented through using land cropped with perennial grasses seeded fallows and new
riceland for elite
propagation and seed rice fields. Red rice plants that appear in the
first year
alfalfa crops following rice do not produce seed because they are cut
out with
each cut of alfalfa for hay.
Red rice
seeds
shed into the soil remain viable for several years
and are able to sprout from a soil depth of
10 cm. Thus the emergence of a red rice seed plowed under in the fall
to depths
of 2 and 10 cm would be 20 to 10 percent
respectively. All plants that emerged would develop well
and produce
seed.
Flooding or
flushing the soil to provoke red rice emergence is an effective means
of red
rice control. The method is particularly useful in cultivated fallows
where a
flood is established after the fallow grown crop has been harvested to
soak the
soil to refusal. The weeds and volunteer rice plants are then killed by
disking
or working the field over once with a chisel or plow. Besides
mechanical
eradication of the soil borne red rice
use of high quality seed rice that is free of red rice and
other weed
seeds is an effective way of controlling repeated infestations.
Red rice
infestation increases without regular rogueing of seed fields or when rice follows rice
continuously.
Infestation will also increase if the grower relies on his own seed
stock for
several seasons or
if the seeding
material is badly mixed.
Seed rice
fields
should be rogued several times during the last part of the growing
season to
eliminate not only the red rice plants but also the mixed varieties or
rogues.
The first rogueing is done at tasseling when the panicles of the early
rices
are visible. The second rogueing is initiated when the seed rice
variety has
fully developed and the rogues can be checked for the absence or
presence of
awns and colouration of the panicles. All awned plants are then removed
from
the seed fields growing awnless varieties of rice and
conversely
all the awnless plants are removed from the fields growing
awned
varieties.
Length and
diameter grading of seed rice has been extremely useful in removing the
larger
diameter red rice grains from the seed of long grain varieties. The use
of such
graders is important in controlling red rice. In the medium and short grain
varieties the only
means of red rice control is the use
of seed and land which is free of red rice because no method of
separation has
as yet been devised. The propagation of seed containing red rice soon
results
in a wild infestation of the soil with red rice strains and further
complicates
the maintenance of pure seed.
Field
inspection
of seed rice fields by the Seed Certifying Agency is carried out 5 to 6
days
before harvest time to establish the varietal purity and identity of
seed rice
and to note the degree of infestation with red rice
diseases and pests. Where required
one additional rogueing may be recommended.
Field inspection together with laboratory analyses of seed samples are
used for
further seed certification. In order for the rice to be eligible for
certification the
seed rice has to
satisfy specific requirements and standards
which are available from an official certifying agency. In
general these
requirements deal with application
procedures field
and harvest
inspections post
harvest seed
movement seed
processing and sampling.
All rice growing areas use these standards as the minimum requirements
for seed
rice.
The Time and Method of Harvesting Seed Rice
The time
and
method of harvesting seed rice are both important as they influence
seed
quality. The practice of water management in seed crops is equally
important.
Drying the fields for harvesting requires the close attention of the
grower.
Care should be taken when drying a field that the water recedes
gradually e.g.
at a rate of 1 cm per day. Day to day observation has to
be carried out
over soil which is
drying in areas where
rice seed is not dormant and able to swell and germinate in the
panicle. If
this is the case the
depth of water in
the rice paddy should be lowered immediately to a minimum and in low lying areas withdrawn completely. To
be of high quality
seed rice must be harvested at the proper stage of maturity. If the
seed crop
is cut when immature field
yields are
reduced and the breakage in threshing is excessive because of the light
and
chalky kernels. If the seed crop is left in the field until overripe the kernels may check.
The
difference
in moisture between the inside and the outside of the kernel is said to
be the
cause of checking or
shattering of the
grain. When too much moisture is removed due to high temperatures stresses and strains occur
in the kernel
which result in the microcracking of kernels. The checking of rice
depends also
on the shape of the grain the
degree of
maturity the variety and growing conditions but the moisture content
still remains the
decisive factor. Insofar as the checking of rice is not only the result
of the
outside (weather) factors but
also of
the mechanical impact it receives during threshing
cleaning
artificial drying and grading
it
is best to employ a method of harvesting that will result in seed with
minimum
damage percentage. Two staged threshing from the windrow is the
preferred
method during harvesting seed rice to reduce mechanical damage. The
combine
threshes about 80 to 85 percent of the grain for seed during the first
pass.
What is left is threshed during the second round. The USSR RRI tests
confirmed
by practical observations of growers have indicated that the least
losses occur
with double stage threshing in which the speed of the thresher cylinder
during
the first pass (peg tooth cylinder 550 rpm and raspbar cylinder 750 780
rpm) is
slower than during the second pass (700 and 1 000 rpm
respectively).
Harvesting
should not be started until 90 to 95 percent of the grain in the
panicle are
fully mature. This is established by taking an average sample. Seed
rice should
be harvested within the shortest time possible and with a minimum
interruption
between cutting and threshing. The normal procedure is to cut rice let it stay in the windrow
for 3 to 5 days to
dry and then thresh
it from the windrow.
Leaving the windrows in the field is unadvisable because of adverse
weather
factors that may cause the grain to check and lower its quality. Where
the two
staged harvest method is used for different varieties
threshing should by all means be done with
thoroughly cleaned combines. To keep varieties segregated use is also
made of
direct combining where the rice plants are not very badly lodged and
the grain
yields do not exceed 5 t/ha. In such cases the drying of the grain can
be
promoted by applying such chemical desiccants as magnesium sulfate
which has
proved useful in seed fields in testes conducted in various rice areas
about
the country. Spraying magnesium chlorate at 25 kg/ha hastens the drying
of the
grain and straw by 10 to 12 days. This practice prevents lodging reduces by 10 to 15
percent the checking of kernels and
permits direct combining. No grower
however
should use a desiccating material on the maturing seed
crop until he has
checked its legal status with reference to chemical residue tolerances.
Rice Culture
Rice in the
Soviet Union is an artificially irrigated lowland crop seeded directly
onto the
check. Nursery transplanting is not practiced.
Modern
cultures
of rice in this country rely on the policy of ever increasing rice
production
based on the use of engineered rice systems
mechanization fertilization and the latest advances in
agricultural
sciences and practical rice farming.
Each
of the country s rice
producing areas has incorporated practices of growing and harvesting
rice which assure
high yields (6 7 t/ha) of good
quality paddy rice.
Crop Rotations
In most
rice
growing farms crops are rotated because under continuous cropping with
rice the
soil becomes depleted in fertility and organic matter. The resulting
deterioration of the physical condition of the rice soil makes
cultivation
difficult and the soil becomes infested with weeds and diseases that
reduce the
yield and quality of the rice grain.
Proper
choice
and establishment of a rotation program is very important for
maintaining high
and stable production controlling
weeds
and red rice increasing
the irrigation
water and land use efficiency as
well as
the use of farming machinery and labour. Rice rotations help maintain
and
improve soil tilth and productivity between rice crops
provide nutrious forage for livestock on the
rice farms and increase the total agricultural output per hectare of
riceland.
The preferred system of cropping for any farm depends on the soil type local climatic conditions and economic
considerations. In any case both
the riceland and rice grower should
benefit from crops rotated with rice. Rotational crops are selected so
as to
help eradicate weeds reduce
populations
of injurious pests control
diseases and lower
production costs.
Although
the
biology of rice makes it superior to other crops in that it responds
well to
repeated or continuous cropping rice
in
this country is rotated with other crops for the reasons discussed
earlier.
Rice rotations are also feasible because the increase in rice yields despite a smaller
proportion of cropland in
rice each year due to rotation is
sufficient to maintain or even increase the total rice production on
rice
farms. A high and stable yield of rice under continuous cropping can be however
obtained only with heavy application of commercial
fertilizers. The USSR
Rice Research Institute has reported that the 27 year average yield of
rice
grown in a six year rotation was by 1.73 t/ha more than when rice was
grown
continuously. Rotating rice with other crops is 1.5 times more
economical than
maintaining a continuous rice culture. In establishing a cropping system a four year rotation of
rice gave 0.45
t/ha or 10 percent
more rice than the
first yield. The yields of rice declined 0.47 t/ha within the same
period under
continuous cropping. In rotation experiments in the USSR Far East the yield of rice in a
seven year rotation
system was found to be 1.5 times that of rice under continuous
cropping.
Similar results were reported from the Uzbek SSR Rice Research
Institute.
Continuous
planting of lands to rice leads to heavy infestation of riceland with
the rice
culture related weeds to
the detriment
of the soil s physical condition and depletion of its fertility.
The
beneficial
effect of crop rotation on the rice yields can be attributed to many
factors.
First rotations
enrich the plow line
soil layer in organic matter and eliminate aquatic and other injurious
weeds.
Rotations facilitate oxidation of the chemically reduced nutrients improve porosity reduce the bulk mass by
improving soil
texture (less amount of particles smaller than 0.25 mm). They are also
helpful
in controlling insects and diseases and providing better opportunities
for
surface levelling through timely operations. On commercial rice farms rotations ensure
comparatively high and
stable grain yields.
Rice
rotations
in this country were first used in the old Kuban delta land which were formerly
overgrown with boggy reed
vegetation. An 8000 ha area had been developed for rice and six and
seven year
rotation systems were tried on its low productive
overmoist and partly salinized soils. In the
years 1971 75 average
yields on the rice
farms
Table
1. Rotation vs Continuous
Cropping (the Kuban area)
Rice
rotations
have come into use also in the new Kuban delta ricelands to benefit the
rice
growers with 5.5 t/ha and more rice
which is 1 1.5 tons more than the average yields on the
neighbouring
farms where rotations are not yet customary.
Cropping
systems
or rotations have been used by many rice farms in other rice producing
areas of
the Soviet Union just to demonstrate that crop rotation is essential to
ensure
rice yields of about 6.0 t/ha or
even
more.
Cropped Land Structure
Under a
rotation
program it is sought to use a maximum of cropland in rice following
crops that
are proven the best predecessors or
forecrops. Such crops for rice are those that improve soil productivity
and
help the rice grower obtain good returns from a hectare of cropland.
For this
purpose the
irrigated ricelands should
for the greater part of the year be preferably used for raising high
yielding
crops. Since livestock has been extensively developed in most rice
growing
areas such crops
are grown basically for
feed purposes. In this way crop
rotations are a useful tool in matching up the cultivation of rice and
livestock raising.
Usually the
rice
systems are designed and engineered for a particular rotation pattern.
The
choice for a cropping pattern is therefore very important the determining factors
being agricultural
specialization soil
type water and
drainage conditions in the
locality and the
agronomic function of
the rotation system. The idea of crop rotation implies that crops be
periodically changed e.g. flooded rice is followed
by a dryland crop.
Such alternation of crops is mutually beneficial because it helps
eliminate the
deteriorative effect on the rice soil of extensive floods by allowing
the soil
to dry out when it is in a dryland crop. The cropping systems should be
selected so that the proportion and the order of crops in the cropland
are
easily adaptable to different economic situations without readjusting
the
irrigation facility layout. Research and farming have proved that long
time
rotations such as
the seven eight
and nine year rotational programs
are most suitable in this respect.
Of the
numerous
long time cropping systems the
eight year
rotation with perennial grasses and seeded or cultivated fallows is
preferred
as the most flexible one. Under such a cropping pattern
62.5 percent of the land is used for
rice this
proportion being easily
increased to 75 percent when necessary. The rice soil benefits from
this system
in receiving a double amount of organic matter
first from turning under the perennial grasses then from the annuals. In
addition the eight
year rotation system provides
better opportunities for the basic land forming and levelling
operations in
each field check. In most rice producing areas
this cropping pattern has been the basis for design and
construction of
new riceland developments. Also other
scientifically grounded cropping systems involving rice for various
periods
have been in use on rice farms of other locations in the Kuban delta
lands.
The Krasnodar Territory
Many rice
farms
use the eight year rotation with the following orders and frequency of
crops first two
years perennial
grasses (alfalfa clover)
third to fifth year rice sixth year
seeded fallow followed
by two
annual crops of rice (with 62.5 percent of the land being used for rice 25 percent
for perennial grasses
and 12.5
percent for
cultivated fallows under
the system). About one fourth of the
cropland in the Kuban delta is in a seven year rotation
first and second year. Perennial grasses
(alfalfa clover) third to fifth year rice
sixth year cultivated
fallow and seventh
year rice
or first year cultivated
fallow second and
third year rice
fourth year other
grain crops
overseeded with perennials fifth
year grasses
and sixth and seventh year rice (with 57.1 per cent of
land in rice under
the system). Where the long time
rotation is impracticable but
the
agronomic practices are advanced and
labour and power resources are plentiful
the rice growers choose to use short term cropping systems such as the three year
rotation first year
seeded fallow and second and third year
rice (with 66.7 percent of the cropland in rice) and four year rotation first year
cultivated fallows and three years in rice
i.e. three fourth of the time the land being
used for rice under
the system.
The Don Piver and Cis Caspian Lowland
Depending
on
local conditions and economic considerations
rice growers here may choose between six
seven
and eight year rotation systems.
In a six
year
rotation the
frequency of crops is first
and second year perennial
grasses third and
fourth year rice
fifth year seeded
fallow (spring
grain crops) and sixth year rice
(with
50 percent of land in rice 33.4
percent
in perennial grasses and
16.6 percent in
seeded fallows). Also row
crops and
pulses may be fallow grown in some localities.
The seven
year
cropping systems recommended for these areas are similar to those used
by the
rice growing farms in the Northern Caucasus. The fallow grown crops may
vary
with the locality from winter wheat
pulses or spring barley in eight year rotations (with 62.5
percent of
land in rice) to vegetable crops in
seven year rotations.
The USSR Far East
In the
Monsoon
climate of the Far East the cropping patterns vary. The eight year
rotation may
have a different order of crops depending on the depth of snow pack in
the
winter. Thus in
localities where snow
cover is permanent an
eight year
rotation may be first
to third year rice
half of the fourth year
green
manure crop the
other half maintenance
of the irrigation
facilities fifth
and sixth year rice
seventh year barley
or oats over
cropped with clover eighth
year clover (with
62.5 percent of the land in
rice). Where snow is marginal the
order
and frequency of crops is first
to third
year rice half of the fourth year green manure crops the other half maintenance of
the irrigation
facilities fifth
and sixth year rice
seventh year cultivated
fallow and eighth
year forage crop
the percentage of land in rice being the same. In other
localities recommendations
are for a seven year rotation
as follows first
year grain crop
second year feed
crop third and
fourth year rice
fifth year green
manure crop sixth
and seventh year rice
(with 57 percent of cropland being used
for rice). A six year rotation allows for one year in grain crop two years in rice one year in soybeans for
green manure and two
years in rice (with 66.7 percent of land in rice). The practice for
newly
developed ricelands has been a four year rotation consisting of three
years in
rice followed by half a year of green manure crops and the other half
used for
maintenance of the irrigation facilities (with 75 percent of land in
rice under the
cropping system).
The Ukraine Uzbekistan and Southern Kazakhstan
With
allowance
for the local traditions and climate
the
cropping patterns are essentially the same but may vary in length from
four to
nine years also in
the order of crops
and in the proportion of land in rice
which may range from 43 to 66.7 percent. Whatever the
order and
frequency of crops in rotations rice
growers have to follow the general tendency of crops in rotations rice growers have to
follow the general
tendency of allotting a maximum and economically feasible proportion of
the
land to rice as a staple culture and
grow catch crops on it in between rice croppings.
Intensified Cropping Systems
Because of
the
high cost of land development for rice
one way to ensure good returns from a hectare of irrigated
land is by
putting the riceland to intensive agricultural use. Considering the
limited
geography of rice in this country
another way is to extend the acreage for rice in a
rotation in addition
to increasing the yield of rice through improved agronomy and superior
varieties. Research on rotating rice with other crops has proved it
possible to
repeat rice cropping (up to four years) in the same field. Obtaining
high and
stable yields under such a system of cropping requires periodic
incorporation
into the soil of organic matter optimum
applications of fertilizer good
water
management sufficient
treatment of the
field with herbicides and
adequate
agronomic practices. Rotational experiments conducted by the USSR Rice
Research
Institute indicate that the yield and gross output of rice can be
increased
through using rotations making
better
use of perennial grasses increasing
to
more than three years the length of repeated cropping of rice after
perennial
grasses and through
growing catch crops
between rice croppings.
The eight
year
rotation system developed by the researchers for the Kuban delta
ricelands can
be considered as intensified rotation with 75 percent of land in rice.
The
coefficient of land use under this system increases from 1.25 to 1.75
due to
growing catch crops and better use of perennial grasses.
Time
2. Rotation of Rice with and
without Catch Crops
Forecrops
The growth
of
agricultural plants and cultural methods used for soil cultivation and particularly
application of water and
fertilizers cause
various changes in the
physical chemical
and biological
properties of the soil. This in turn affects the growth and development
of
crops that are grown on the same field the following years by
increasing or
decreasing their yield. The knowledge of how the individual species or
groups
of plants may influence the crop grown in alternate years is very
important for
appraising these plants or species as the forecrops
for setting the proper order and frequency of
crops in a rotation.
It has been
proved by many tests and practical rice farming that perennial legumes fallow grown annual
legumes and green manure
crops leguminous
gramineous mixtures and
cruciferous plants and
catch crops grown
for seed and green manure are best for growing in rotations ahead of
rice.
For other
rice
growing areas the
crops preceeding rice
in rotations are essentialy the same. In addition
sweet or sour clover
crimson clover mixed with berseem or Egyptian
clover are sown in Kazakhstan Uzbekistan
and Turkmenia. The Sudan grass and spring wheat are grown in fallow
fields and
as catch crops in the Ukraine and Kazakhstan
while corn (maize) sorghum joughara mixed with mung
beans sweet clover
and vetch oats mixtures are sown
in Kazakhstan Uzbekistan
and Tajikistan.
The rice
soil
benefits much from alfalfa and clover if grown for two years. The
grasses
improve the physical condition of the soil
increase the content of organic matter and soil
productivity. Perennials
facilitate the conversion of almost insoluble phosphorus compounds into
readily
soluble ones whose quantities tend to increase with the age of grasses.
With a
two year old grass cover the
soil has a
maximum of available phosphates. In rice rotations the total yield of
alfalfa
hay (four cuts) may reach 8 10 t/ha with the cost of one feed unit much
lower
than that of annual legumes. High yield of alfalfa in rice rotations is
due to
good agronomic practices including check flood irrigation or sprinkling
and
fertilizer applications.
The
beneficial
effect of alfalfa on the rice soils is higher when the two year old
grass is
left over winter to be turned under the following spring after the
first cut of
hay. In this case it
gives additional 25
30 t/ha of green matter (5 tons on dry matter basis) before the field
is sown
to rice. The method of turning under alfalfa in spring has become
customary
with the rice farms in the Kuban rice areas ensuring stable yield of
good
quality hay in addition to 5 t/ha of early of mid season rice each year and increasing the organic
matter in the soil
in the form of roots and other plants debris. The higher the yield of
perennial
grasses grown ahead of rice in rotation
the higher their beneficial effect on the rice soils and consequently
on rice yield. Grasses
therefore
must be given the best agronomic care including seasonal irrigation and
fertilizer treatments combined with soil slitting to produce highest
yields of
hay already in the first year.
Modern
agronomic
practices and adequate timing of optimum nitrogen and phosphorus
fertilizer
applications make it possible to maintain and sometimes increase the
yield of
rice grown three years continuously after grasses.
The yields
of
rice in an eight year rotation depending on the forecrop were as
follows (the
data of the USSR RRI).
Practical
rice
growing in the Kuban ricelands showed that alfalfa grown for two years
ahead of
rice and plowed under in the spring before seeding rice gives assured
5.0 5.5
t/ha of rice grain and
with
fertilizers up to
6.0 7.0 t/ha. Similar
yields of rice in grassland broken at fall are attainable only with the
application of 90 100 kg/ha of nitrogen fertilizers and phosphates (P2O5).
Fallowing
The chief
aim of
fallowing fields is controlling weeds
check land leveling and
reshaping
and maintaining water structures. But because the land development for
rice is
costly it is unwise
to allow the land to
lie idle and hence
pure fallowing is not
encouraged. The fallow fields are therefore seeded or cultivated which
permits
the chief aim of fallowing to be achieved plus the fallow grown crops
additionally gathered.
Seeded
or cultivated fallows are
fields used for growing various agricultural crops which when ripe
leave fields
free from plants soon after harvest for the land leveling operation.
such crops
in the Northern Caucasus are winter wheat mixed with winter peas or
vetch grown
for hay or green chop spring
vetch mixed
with oats winter
and spring peas mixed
with oats or barley and
winter barley.
The fallow grown crop in the Lower Volga rice farms is mostly winter
rye mixed
with vetch for green chop. In the Far East ricelands such crop is
soybeans.
The use of
mineral fertilizers for the fallow grown winter crops is mandatory in
all the
rice producing areas. The rates vary with the area and soil
productivity. The
soils in the Kuban delta lands require 120 kg N in addition to 90 kg
P2O5 per
hectare applied as basal fertilizer during the fall plowing for grains
in
pulses. Nitrogen applications are split into 90 kg/ha at seedbed
preparation
and 30 kg/ha as an early dressing.
For early
spring
crops such as barley wheat
peas and oats mixed with vetch and peas
the fertilizers are applied at seedbed preparation or at harrowing.
The
yields of vetch and oat
mixtures sown in fallows for hay are about 5 t/ha
winter wheat and peas produce by early spring
3 to 4 t/ha and winter peas sown in autumn produce up to 3 t/ha of
nutritious
green matter.
All these
crops are
however susceptible to excess moisture. Crop failures may result from
too much
water held in checks after heavy rainfall and cloudburst unless
adequate
drainage is provided.
The choice
and
composition of fallow grown crops relies on the economic considerations availability of seeds and the possibility for
annual land levelling
in the checks which
is a key operation
for obtaining high rice yields the following season. In selecting and
allotting
lands to the accompanying crops of rice rotation and fallows the physical condition of
the flooded soils
is particularly important. Alfalfa
barley corn
and peas do not grow
well where drainage is poor and the water table high. Their yields are
low from
excess water and poor thin stands. Adequate drainage is therefore the
only
remedy from water logging and inundation of rice fields and the
adjacent
areas which are in
dryland crops. Of the
crops which can
tolerate high ground
waters crimson
clover berseem
(Egyptian clover) and
mung beans are the most tolerant.
Benefits to
the
staple rice culture from cultivated fallows in the rotation are high
only with
good weed control proper
grading and
levelling of land and
increased organic
matter in the soil due to fallow grown annual legumes and grasses. The
intensive
use of land through seeded fallows makes possible double cropping of
riceland
so that two crops are harvested the same year
provided all operations are expertly timed.
Catch crops
Double
cropping
implies growing catch crops for use either at fall or early next spring
as feed
or green manure the same year after the main fallow grown crop is
harvested field
levelled and given the
semi fallow tillage. Growing catch crops is also important for
improving soil
productivity and rice yield. The name catch crop applies to crops grown
the
same year following the staple crop and intended for feed or green
manure. They
are also known as stubble crops. The term is also applicable to crops
sown in
the spring into the cover crops to keep growing still for some time
after the
cover crop is harvested. Such crops are also called the companion or
nurse
crops the name
applies to crops sown in
summer or in the fall following the staple crop and harvested for feed
purpose
the following spring before a main crop is sown
and known as the wintering crop
and also to crops sown on fields free from the previous
crop harvested
early in season for green chop sillage
or hay and
sometimes called the
postharvest crops which elsewhere can be grown as the main crop.
The
agricultural
plants selected to be grown as catch crops should be high yielding and
early
maturing recommended for this or that area
and well adapted to heavy and periodically flooded soils.
Among such
crops are pulses (winter and spring vetch and peavine)
winter rye
winter wheat barley oats
spring rapeseed all
sown in pure or
mixed stands.
In the
Northern
Caucasus and the Lower Volga rice areas the fallow grown catch crops
are sown
in the summer or fall and thus are called summer crops. The same crops
to be
grown in rice fields are sown as winter crops. In the rice producing
areas of
the USSR Far East the catch crop is soybeans (when grown in fallows it
is for
green manure although
soybeans can be
grown for grain).
Winter rye
is
good as a catch crop. Some of its winter varieties are winter hardy and
shoot
out well early in the spring at low temperatures (close to zero) producing fairly good
yield of nutritious
green matter so
valuable early in the
spring for its vitamins.
In many
rice
growing areas of this country and particularly in the Cis Caspian
Lowland rotational
crops are grown in saline soils.
In such cases adequate
drainage and
importation are necessary to avoid water logging
inundation and salinization of the land in
accompanying crops and grasses that are adjacent to rice fields on the
one
hand and make the
best use of the
rotation on the
other. Of the
accompanying crops peas oats and corn are less
tolerant to salts than
are rye wheat sorghum
and particularly alfalfa. Gourds and melons tolerate
better high
concentrations of salts. Soils moisture content is an important
regulator of
the degree of salt tolerance of the rotational crops. The higher the
moisture
content the more
tolerant the plants to
salinity during their early development.
To provide
high
and stable yield each
rotational crop in
a rice cropping system should be grown under optimum agronomic
conditions. It
has been established that the rice yield to a large extent depends on
the
productivity of the preceeding crops. Thus
yield or rice following one year alfalfa
depending on its crop of hay
was
as follows
Good timing
of
catch crops is also important in a rice rotation. It is advisable that
in the
rice fields which
are planned the
following season for catch crops rices
are early maturing and sown in the current year as early as possible.
In that
way the crop of rice is ready to harvest much early giving the grower
time
enough to prepare the land for catch crops of the following year.
Land Preparation
Tilling
soil for
rice is not much the same as tilling for other cereals and dryland
crops. Its
principal aim in rice production is to obtain high yields of rice
through
improving the rice soil and taking advantage of its potential
productivity.
While the
dryland crops require soil nutrients in the oxidized form the rice plant benefits
more when the
nutrients are chemically reduced or deoxidized. The dryland crops
require that
the capillary noncapillary porosity ratio (determined by the water
stable soil
structure and soil moisture brought to capillary capacity) be optimum while this soil parameter
for rice is
practically for rice is practically unimportant.
Nutrition
of the
rice plant is in large measure assured by inundation during part of all
of the
growing period. Flooding is very much essential for optimum grain
yields that
are why the ideal soil types for rice production are those that
conserve water.
Most rice soils often
referred to as
heavy soils because of their high clay and silt content
present special soil management problem that
are overcome through soil cultivation practices intended also to help
make the
best use of the natural soil potential. These measures include tillage
and
seedbed preparation maintenance
of organic
matter and soil texture drainage
for
successful mechanized rice operations
cultivation of other crops in rotation with rice fertilizer application use of green manures and weed control.
Soil
tillage
practices vary from place to place depending on soil type climatic conditions crop that preceedes rice
in rotation physical
condition of the soil character
and degree of field
infestation herbicides
used and other
factors. Tillage in rice production pursues many purposes which are generally aimed
at
Forming
a sufficiently deep and biologically
active plowline layer by working the field several times over with
various
types of plow
Creating
conditions in the plow
line that help immobilize soil nutrients
i.e. regulate oxidation and reduction through loosening drying and aerating of soil
Wetting
the rice fields that are
to be sown at early dates and to a greater depth so as to establish the
moisture content sufficient to bring about emergence of rice seedlings
without
additional flush irrigation
Preparing
the riceland with a
soil structure that will ensure a uniform coverage and germination of
seeds good stand
establishment and
further development of the plant during growing season
Controlling
weeds pests and
diseases of rice and other
rotational crops by plowing in the fall one time over with a chisel and
a
second time in the spring with a mouldboard
Precise
levelling of the field
surface (to within ± 5 cm from the median plane of the rice check
surface) to
maintain desired depth of flood water in the field and to drain as
rapidly as
required
Covering
organic and mineral
fertilizers at desired depths
Preparing
a suitable seedbed for
rice.
Harvest and Post
Harvest Operations
The harvesting of mature rice
and post harvesting
operations are important aspects of rice culture. Rice crops usually
mature
later in the season than other grain crops. The time to harvest rice
therefore
varies from early September in the European USSR to mid September in
the Far
East. For the best results harvesting should continue for no more than
20 25
days. Delaying or extending the time of harvesting increases losses reduces both yield and
grain quality and
does not provide enough time to
adequately prepare the land for next season s crops.
Factors
that
determine the duration of the harvest are the time and date of seeding
the
maturity period of the rice variety
the
level of infestation soil
and drainage
conditions in the rice fields and
the
weather before and during harvesting.
Draining for the Harvest
Draining at
the
proper time before harvesting is required to sufficiently dry the soil
to use
the heavy rice harvesting machinery. It is
however equally
important to
maintain the water in the rice field long enough to permit the rice
crop to
reach proper maturity.
When to
drain
depends on the soil type drainage
facilities and
weather conditions in any
given season. Some soils dry quickly
others slowly. Rice growers soon familiarize themselves
with the time to
dry their soil and
soon learn to judge
when the best time is to drain the fields
for harvesting without letting the rice crop suffer from a
lack of soil
moisture. In a year with a typical amount of heat and rainfall the date when rice will be
ready to cut can
be estimated by observing the date of flowering and initiation of
heading. Rice
normally requires 40 to 50 days from flowering to maturity.
The flow of
water into the checks is usually reduced by the time rice reaches the
soft
dough (milky) stage and
is discontinued
altogether when the rice matures to the hard dough (waxy) stage so that
the
water will recede slowly at a rate of 1 1.5 cm per day. Where the soils
are
saline the fields
are drained. The level
of groundwater should preferably be maintained low through proper
drainage to
avoid waterlogging the checks. Less time is required to dry the soil
where
drainage furrows have been opened in the spring. In fields without
drainage
furrows pools of
water are likely to
appear. In such cases the
water is either
pumped out or removed through hand made furrows.
Usually
riceland
may be drained when the rice crop has fully headed and the panicles
have turned
down and ripened in
the upper parts.
This stage normally occurs about 2 3 weeks before the rice crop is
ready to
harvest.
Water
intake
should be discontinued progressively beginning with the low lying
checks that
are usually downstream from the headwork
then successively with the checks at higher elevations.
This results in
a simultaneous and uniform drying of the paddies in each large check.
By the
time the rice crop is ready to cut
the
soil should be dry enough to support the harvesting machines and
equipment.
Premature
drying
of the field checks will delay the filling of grain
so the rice crop harvested too early will
have a greater quantity of immature
empty and poor quality grains
and
will produce a smaller yield of head rice at milling. On the other hand it is equally important
not to miss the time
of maturity. When rice stands too long in the field
losses are increased due to lodging
premature germination in the panicle
and shattering.
Pre Harvest Chemical Drying
The pre
harvest
application of chemical desiccants is a frequently used practice to
speed the
drying of rice in the field before harvest. Of all the known materials
applied
as sprays a 60%
magnesium chlorate water
solution has proved the most effective when it is used at 25 kg to 150
liters
water per hectare. After treatment with this desiccant
about 2 3 percent grain moisture and 4 6
percent leaf moisture is removed daily. Within 4 to 6 days as soon the grain moisture
content is brought
down from within 20 27 to 15 16 percent
the rice can be harvested.
The aerial
application of desiccants gives best results when carried out on clear
bright
days early in the
morning or afternoon.
Average diurnal temperatures should be about 9 10°C with a maximum wind
velocity of 4 m/s. Very good results are obtained if there is no rain
for about
6 to 8 h after spraying. The application of chemical desiccants at
optimum
dates (when 85 90 percent of kernels are fully mature) increases the
grain
yield improves the
seed quality and
reduces both labour and harvest time by
10 to 15 days. Rice treated with desiccants is usually harvested by
direct combining.
Chemical
materials used as desiccants should be considered poisonous so no grower should use a
desiccating
chemical on the maturing rice crop until he has checked its legal
status with
reference to chemical residue tolerances. When used with caution however
desiccants can give good results without the traditional
after effect
such as a drop in milling quality
kernel
dislocation and an
off flavour that
may occasionally be imparted to the rice.
A new
method of
speeding up the drying of rice has recently been proposed by Professor
E.P.
Aleshin [8] and has
proven effective in
improving harvesting conditions and grain quality
and in reducing harvest losses. It relies
entirely on a solution of water soluble phosphorus fertilizers plus
small
amounts of 2 4 D amine salt which
is
applied as a top dressing on rice in the milky stage of ripening.
Pre Harvest Operations
After the
irrigation water has been withheld and the soil is sufficiently dry the rice around the check
s border is cut
with either a self propelled crawler mounted reaper
a combined harvester thresher
or a crawler mounted swather. This is done 2
3 days before the all out harvesting of the rice begins in the fields
enabling
more time for the soil to dry out and the rice to mature as well as eliminating the
risk that the
harvesting machines will run onto hydraulic structure
invisible to the operator.
Square
shaped
rice paddies and large checks are divided into strips 50 to 70 m wide
by
cutting swaths from one end of the field to the other. Two cross swaths
are cut
from both sides of the field to provide a 6 to 10 m wide headland for
the
harvesting equipment. This increases the efficiency of the harvesting
machines
by about 15 to 20 percent reducing
hand
labour and field
losses.
The time to
harvest food and seed rice can be determined by observing the date when
85 and
95 percent of the grains in the respective panicles are fully mature.
If the
crop is left in the field until it is overripe
the kernels may check. This will cause breakage during
combining and
milling and a
reduction in the yield of
whole kernels (head rice). Biological yield losses from harvesting
delayed by
three days amount to about 0.2 t./ha. The losses rice to 0.5 1.0 t/ha
when
harvesting is delayed by 10 to 15 days. It follows that the prime time
for
cutting the rice crop should not be missed by the grower. Any delay
will result
in reduced yield due to shattering during hot
dry days and slow threshing if the weather is humid and
cool.
The time to
harvest depends largely on the weather. The mid season varieties of
rice (Kuban
3) which are sown
about the same
date should be
harvested within 8 to 10
days and the late
rices (Krasnodarsky
424) within 10 12
days. It has been established
that standing rice does not hold its maximum yield for long. In the
Kuban river
riceland for
instance rice keeps
its optimal grain yield (to within
± 5 percent of the maximum) only 8 to 10 days.
Harvesting Rice
Most rice
in the
Soviet Union is harvested mechanically either with self propelled
combine
harvesters or with
a tractor drawn
header or swather which threshes from the windrow. Harvesting by hand
may be
resorted to only on very small acreages when the weather is rainy and
the use
of harvesting machines is impractical.
Direct
combining or single
phase harvesting and
separate
or two phase harvesting are the two major methods to
harvest rice in
this country.
Over 80
percent
of the total rice acreage in the USSR is harvested by the two phase
method.
Essentially this is
cutting the rice
with a swather or windrower and
threshing it from the windrow with a pickup combine when the grain is
adequately dry. The rice is then dried artificially before it is stored
or
milled. Careful adjustment of the reaping machine and the thresher
leads to
grain of a high milling quality and market value.
The two
phase method
permits rice to be cut at earlier dates
followed by threshing from the windrow 3 5 days after.
This results in
grain with much less moisture content
thus reducing the cost of artificial drying. If the rice
crop is left in
the windrow too long the
grain may check
(crack) increasing breakage during threshing and milling and markedly reducing the
yield of head rice
and quality of seed rice. It is therefore better to thresh from the
windrow at
the proper time and avoid large intervals between cutting and threshing.
Direct
combining
or combine harvesting is more efficient and economic in that it
provides grain
of the highest milling quality and considerably reduces fields losses.
It is
more effective over the two phase method
particularly when the weather at harvest time is unstable because it permits rice to
be removed from
the field in one operation with no danger of weather damage. Hopefully with improved combines
along with a wider use
of desiccants grain
driers cleaning
facilities and less lodging rice
varieties that produce less vegetative growth
direct combining will find a wider application in the near
future.
Already in
some
rice growing areas self
propelled rice
combines provide the major means of harvesting rice.
With either
method obtaining a
control yield of
threshed grain by cutting and threshing 2 swaths in 2 3 representative
(typical) field checks or rice paddies has become an important practice
in all
rice producing areas. Practical observation confirmed by growers results indicate that the
operator is the
most important factor in preventing high combine losses. Therefore control threshing is
usually done first by
highly skilled combine operators who determine for the other operators
where to
adjust the thresher device in the combines
and the cutter head in the swathers and reapers.
With the
common
two phase harvest method rice
is cut
with a tractor mounted side delivery windrower or reaper. Front mounted
swathers having two active cutter bars are good for cutting badly
lodged rice.
A header or windrower is also suitable in such cases as it delivers
uniform
windrows from 4.5 to 5 m wide swaths. Such windrows dry quickly. Self
propelled
headers or swathers with the knife divider removed and the reel
adjusted to the
rear shield of the frame can also be successfully used to cut rice
crops that
are badly lodged. These adjustments reduce the number of cut out
panicles lower
losses by reel shattering and
improve the operating condition of the
reel and the delivery chain. The cam action reel should be adjusted 200
250 mm
frontwise relative to the cutter so that the rake just touches the
plant stem
at 2/3 of its height from the base. The reel is adjusted in level with
the
cutter bar to cut lodged rice below the point of bending i.e. 50 70 mm from the top
so that the reel
rake then only cleans the knife and pushes the cut plants onto the
delivery
chain. The reel speed should always exceed the ground speed of the
swather.
This effects proper reaping at 15 20 cm from the ground surface and
minimizes
field losses. The height at which the rice is cut is very important
because the
proper amount of straw serves as a cushion to the grain during threshing resulting in a lower
cylinder loss and less
breakage.
Rice in a
paddy
or large check may be cut either by the strip or by the continuous
method. With
the first method each
swather or combine
works a strip of rice crop 50 70 m wide. It starts on one of its longer
sides makes a 90
deg turn at the corner
and an idle run along the shorter side of the strip to turn again and
cut rice
along the other longer side in the opposite direction
working clockwise from the check s field
margin towards the center line of the strip.
Strip
harvesting
is good for harvesting field checks where the swather can pass over the
levees
from one rice paddy to another. The efficiency of the harvesting
equipment is
15 20 percent higher as
the idle run
distance on the head land is considerably reduced. The method is
usually used for
cutting badly lodged rice or
under extremely
muddy conditions when turns are difficult to make due to large clods on
the
headland.
The
continuous
method is effective where soil is more dry and rice is not lodging. The
method
requires no headland as the harvester cuts the rice going
counterclockwise
along the check and makes a turn to the right (270° loop) each time it
reaches
a field corner.
Usually
several
harvesters form a group that completes harvesting a field check within
3 4 days
(15 20 hectares per each swather). The group method permits the rice
crop to be
quickly cut and threshed with a pickup combine as soon as the windrows
are
sufficiently dry. Where the harvest time is late August and early
September and
the days are warm and dry threshing from the windrow is normally begun
3 5 days
after cutting. Where the harvest time is late September and early
October the
interval between cutting and threshing may be longer. Threshing from
the
windrow may not begin until the grain (not the stem) moisture content
reaches
16 to 20 percent. Field observations confirmed by grower s reports
indicate
that if rice is left in windrows until over dried
this results in grain of poor quality
creating heavy losses during threshing and milling.
The
threshing
operation in a field check 15 to 20 ha in size is also done by a group
of 4 to
5 pickup combines. They are assisted by tractor drawn or self propelled
grain
carts which haul
the threshed grain from
the combine to the field side trucks
who in
turn haul the grain
further to the driers or the
elevator. With an average efficiency of 3 4 ha per combine such a
harvesting
team may complete a field check in 2 3 days. In both methods total
field losses
can be minimized and grain quality improved by threshing the rice straw
with
unthreshed grain a second time. Double threshing requires that 85 to 95
percent
of the grain the threshed during the first threshing round while the
remaining
grain is threshed during the second round with a pickup combine
harvester. The
combine thresher should be adjusted so that no threshed grain will go
into the
new windrow as the straw leaves the combine. The windrows should be
uniform in
shape and not too large so that they do not crowd the feed. The more
straw is
fed the higher the
cylinder losses particularly
if the grain s moisture content
is excessively high. Because the rice kernel is susceptible to cracking the cylinders should be
run at a slower speed
than usual for small grain crops.
To obtain
maximum grain yields it is necessary for the cylinder and the concave
to be in
good condition and for the concaves and other parts of the combine to
be
properly adjusted. The major combine losses are attributed to the
cutter
bar cylinder rack
and cleaning shoe. Other losses may be due to overloading
or improper
machine adjustment or
a combination of
the two. Overloading as a result of excessive ground speed is usually a
major
cause for heavy loss in all types and sizes of combines. Modern
combines can be
adjusted to do a good job of threshing with a minimum of shelling and
cracking
of the grain.
With a lath
reel
pickup grain losses are about two times less than with the pegged reel
version
of the pickup attachment. For this reason the lath reel pickup is
preferable to
the pegged reel pickup. High losses of unthreshed grain usually result
from
either improper cylinder (drum) or concave adjustments
or both. Losses of threshed grain may also
come from poor separation in the straw wakers and cleaning shoe.
Several tests
should be made with each machine to determine the effect of adjusting
or
changing the ground speed. Cylinder speed should be varied with the
rice
varieties and the grain straw moisture content.
Table
1. Combine Cylinder Speed
for the First Round of Threshing rpm
Reducing
the
cylinder speed helps minimize shelling and cracking of the grain but may increase the loss
of unthreshed
grain. For the second round of threshing
the speed of the fan and cylinders should be greater than
the rated one
by 20 percent.
Rice
harvesting
machines include various tractor driven swathers and reapers self propelled headers and
windrowers and self
propelled combined thresher
harvesters equipped with crawler tracks
half tracks or tyres. In rainy season wide mud cleats may
be bolted onto
the tracks to increase support to the harvester. Other tractors and
combines
are equipped with tyres with mud lugs or cages
so that they can be operated on the sloping levees and under extremely muddy
conditions.
The rice
farming
machines usually operate by either the traction or floating principle.
By the
first the tracks or
tyres penetrate the
muddy tilth to reach the hard pan on which they find a firm support for
traction. By the second principle
machines have to move by flotation
acquiring support on the top muddy soil with the help of
cage wheel or
track extensions (extendable lugs). Ricegrowers would very much
appreciate
special self propelled rice combines equipped with the
rice special tyre . Some self propelled
harvesters are equipped with large bins or hoppers for collecting the
threshed
grain. The hoppers are emptied by mechanically augering the rice into
self
propelled bankouts or tractor driven carts
that take the rice to
trucks which wait alongside the field. The rice is then hauled to
driers or to
aeration bins where it is unloaded by use of grain augers or other bulk
handling means.
Grain Moisture Content
Because the
grain moisture content varies with the time of day
the combine threshing parts should be re
adjusted several times during the day
at
9 10 a.m. and 6 7 p.m. for the wet straw and between 12 and 4 p.m. for
the dry
straw.
Rice must
be of
high milling quality to command a premium price
and to obtain this high quality and maximum yields rice must be cut at the
proper stage of
maturity (moisture content).
When the
rice crop
has reached the proper stage and grain moisture
harvesting should proceed quickly because the loss of
moisture in
standing rice can be very rapid. If rice is harvested at the proper
stage the grains
are fully mature in the upper
portions of the panicle and are in the hard dough stage at the base of
the
panicle. Observations indicate that maximum yields of head rice were
obtained
when rice was harvested at moisture content of about 18 to 24 percent
and then
immediately dried to 13 and 14 percent. Varieties differ as to the
range of
moisture content at which they yield the best quality milled rice. This
range
is rather wide varying
from 16 to 25
percent for some varieties. Many rice growers determine the moisture
content of
hand harvested samples of their rice with various types of moisture
meters
before they begin all out harvesting.
Thus when harvesting for
maximum quality a
lot of factors must be considered
but moisture content of the grain at harvest
time is among the most important. Good results may be obtained with the
use of
chemical desiccants which
hasten pre
harvest of the crop if
applied timely
and properly.
Post Harvest Operations
Straw Removal and Use
Post
harvest
tillage and preparation for the next crop require that the rice fields
be
cleaned of rice straw and other plant residues. The straw can be
removed from
the field after it is bailed picked
up
and stacked off field to be processed for animal feed. Some other
suggested
uses are as bedding construction
material for
manurial purposes or as a
mulching material for purpose of soil protection. The straw can be
removed from
the fields either as the harvest proceeds or immediately after the
harvest. For
soil mulching the
straw is simply cut in
the rice field with special straw spreaders or choppers and the straw
particles
are then spread uniformly over the stubble to facilitate plowing under
with a
disk plow. Some combines are now equipped with straw spreaders that cut
up the
straw as it leaves the combine. Various other machines such as straw
rakes pickup
choppers stackers
and loaders assisted with special
tractor driven straw carts are used to facilitate the operation and
haul straw
stacks from the fields.
Processing Rice for Storage and Milling
The
cleaning and
drying of rough rice is very important for safe grain storage. Timely
and
proper processing of the field run rice usually results in attaining
grain of
the highest quality and commercial value with lower input per unit
volume of
rice dried and stored. The post harvest procedures include pre cleaning or scalping
drying and grading of the rough rice. Usually the rough
rice coming from
the field unless
the fields are
clean contains
considerable foreign
material such as
stems weed seeds
and trash. It is therefore advisable to clean it partially
with a
scalper aspirator machine before putting it into the bin for aeration.
In some
areas facilities and conditions may require that the rice first be
dried. Such
drying may require that the rice be passed though the drier several
times.
Frequently the rice
is also aerated
between passes to remove foreign matter and light weight immature grains before it
is put into
storage.
Preliminary
cleaning of rough rice can be done on the on farm facilities that
should
include a fanning mill with a wind aspirator to remove light grains hulls and other light
weight foreign
material a screen
with large
perforations to remove any remaining sticks
stems lumps and large weed seeds and a finely perforated
screen to remove fine
broken rice grain small
weed seeds and
other small particles of foreign
material. The pre cleaned rice is then put into bins for aeration.
Aeration
Is the
procedure
used to cool and ventilate grain during storage to improve quality and
prevent
spoilage. This can be accomplished by turning the grain at regular
intervals by
transferring it from one
bin to another with a grain loader or grain thrower
or by circulating air through the stored
grain.
For proper
drying moisture
must be removed from
inside the rice kernel. Drying too fast can result in internal cracking
or
checking of the kernels. To prevent this
drying is usually done in several stage with the moisture
reduced only
about 2 percent at each drying. After each stage
the rice is tempered in a bin so that the
kernel moisture will equilibrate.
Weeds and Their Control
Weeds
compete
with rice for light nutrients space
and water they
also adversely
affect the microclimate around the plant
and harbour diseases and pests. They reduce yields lower the market value of
the crop by
reducing quality and
increase the cost
of production harvesting drying and cleaning.
Slightly
more
than 250 species of plants have been registered as weeds that infest
rice
fields in the Soviet Union. Of these
about 20 species are persistent weeds that infest old
ricelands and some
10 12 species are weeds frequently
found in crops that are grown in rotation with rice.
Weeds that
infest rice fields differ from those
that infest dryland and even irrigated crops. They are from the species
that
thrives best in extremely wet or flooded soil.
Plants that
infest rice fields can ecologically be grouped as hydrophylous marshy
aquatic and floating weeds
and
algae.
Hydrophylous
weed plants include barnyard grass (Echinochloa contracta Stev. E. phyllopogon Stapf. and E. crus galli L.).
The weeds
in
this group are common to all rice growing areas and grow equally well
in
waterlogged soils and fields flooded with shallow water. Prolonged and
deep
flooding is fatal for the young weed grass.
Barnyard
grass
is an annual plant and is the most persistent weed in seed rice and
food rice
plantings. Early in season it is often hard to differentiate between
the young
rice seedlings and those of the weed grass because of various
morphological and
biological characters that are quite similar in both species. However the rice leaf is more rigid robust and rough than that
of the barnyard
grass which has a
wider vein in the
centre and is a
paler green. The stalk
in rice is somewhat flat at the base
and
it is round in barnyard grass.
Table.
1. Young Rice vs Young
Barnyard Grass
One
barnyard
grass plant may produce from 600 to 800 seeds in average rice stands
and from 3
000 to 6 000 seeds in
thin stands. The
heat requirement of barnyard grass is about the same as that of rice.
Echinochloa spp. germinates at temperatures not lower than 12°C in very
wet or
flooded soils. The optimum temperature for germination is from 20 to
25°C. Shed
in the soil the
weed seed remains viable
for 3 years it may
germinate and give
seedlings in dryland from a depth of 6 cm when the soil is compact and from 12 cm when the soil is loose. It
germinates and
sprouts seedlings from topsoil covered with a shallow layer of water
about 1 3
cm.
Echinochioa
contracta Stev. tillers well in rich soils and in thin stands. It can
be long
awned medium awned and awnless. All three
forms of the species
are subject to shattering thus
infesting
rice fields badly. The weight of 1 000 grains varies from 6 7 g to 11
g. The
matured seed has no dormancy period and since it sheds in wet gound it germinates rapidly from
late September to
early October when the soil is sufficiently moist
the weather warm and
temperatures about 16 18°C. In the
spring the seed of
the weed sprouts from
a soil depth of 1 12 cm as soon as the soil temperature reaches 12
14°C. By
late May its
germination percentage is
about 93 98. The best soil conditions for sprouting are a soil moisture
content
of about 90 100 percent of the least field capacity
and a temperature of 20 to 25°C. In the
spring 100 percent
of the weed seeds
germinate and sprout from a 1 3 cm soil depth
80 percent from a 5 cm depth
and
56 percent from a 10 12 cm soil depth in rice fields where a flood
about 15 cm
deep is maintained. After a year in rice
about 20 percent of the seeds within a soil layer from 0
to 20 cm may
still be viable. The young grass can stand shallow water but a flood of about 25 cm
would be fatal.
Echinochloa
phyllopogon Stapf. can be either awned or awnless. The awnless forms
shatter
more and infest rice soils directly. The awned from are more resistant
to
shattering and infest rice fields through uncleaned seed rice. The weed
has a
well developed root system and produces many tillers. 1 000 grains
weigh 4 7 g.
The seed is not dormant and germinates rapidly producing vigorous
seedlings at
excessive soil moisture and soil temperatures of 14 15°C. The young
weed grass
can stand deep water but floods up to 25 30 cm in hot weather will kill
the
weed within 5 to 7 days. Morphologically E. phyllopogon is closer to
rice than
other forms of the species and has about the same maturity period. The
seed of
the weed buried deep in the soil remains viable up to 5 years and is able to sprout in
compact soil up to
10 cm deep. The seed however fails to produce seedlings
from a soil layer
of 2 cm under submergence but
the
established seedlings can stand deep water for the rest of the growing
period.
Echinochloa
crus
galli L. can be long awned medium
awned or awnless.
The long awned forms
usually infest fields where rice is cultivated under continuous
submergence.
The weed can sprout from a soil depth of 3 5 cm in a field with a 10 cm
deep
water cover but it
fails to produce
seedlings through a layer of water as high as 15 20 cm.
Because
they are
ecologically closer to dryland weeds
the
medium awned and awnless forms normally infest rice fields under
rotational
irrigation. These forms of barnyard grass mature even earlier than do
the early
rices and shatter
more than other weed
grasses. The small sized seed has a period of dormancy. The 1 000 grain
weight
varies between 1.5 and 2.0 g. Once shed
the seed volunteers in early April from a soil depth of 1
cm but not until
mid April from a depth of 3 5
cm. In the spring up
to the time for
seeding rice about
80 percent of
barnyard grass seeds present in a soil depth of 1 5 cm will emerge and about 50 percent will
sprout in a soil
layer between 0 and 20 cm provided
that
air temperatures are 12 to 23°C and soil moisture accounts for 70 to 85
percent
of the least field capacity. When irrigation water is provided from
April 16 to
May 20 about 28
percent more seeds that
survived the winter within the 0 20 cm soil layer will emerge. However about 17 percent of such
seeds will still
remain within the rice field. Under rotational irrigation water applications for
crops other than rice
(usually grasses) can during
one summer
in a dryland crop yield
up to 95 percent
of barnyard grass plants from the 1 25 cm soil layer. E. crus galli is
a viable
plant that grows back every time the main crop of grass is cut.
Rice
cutgrass
(Leersia oryzoides L.) a
perennial
grass has recently
become a problem in
Uzbekistan Kazakhstan and in the Northern
Caucasus. The weed grass
infests primarily rice fields under rotational irrigation and also irrigation
ditches. It propagates by
seed and other propagules called
rhizomes. During its growing period one rice cutgrass plant produces
rhizomes
up to 1 m long with 12 15 internodes. The winter buds start to grow in
the
spring when temperatures are from 8 to 12°C. The culm of the plant
varies in
height from 50 to 150 cm and
its leaf is
sharply indented on the edges. The inflorescence is an expanded panicle
up to
18 cm long that
bears many spikelets
(from 500 to 700).
Marshy weed
plants are largely perennials that infest fields
which are continuously in rice
as well as low lying fields checks
which are waterlogged most of the time. The
weeds in this group thrive exclusively or waterlogged and submerged
lands and can
withstand deep water and prolonged
submergence. The weeds propagate by seed
and by vegetations. Their propagules are rhizomes tubers
or root tubers. These start to grow in the spring at soil
temperatures
about 10 11°C. Because it seedling usually emerge earlier than those of
rice they compete
vigorously with each
other for the growth essentials.
Common reed
(Phragmites communis Trin.) thrives in waterlogged areas and ricelands
where
table water is high. It propagates vegetatively through its well
developed
rootstock that penetrates soil to 1.5 m
as well as through above ground propagules that creep over
the soil
surface. The common reed has no special soil requirements and grow well
in both
saline and good soils.
Bulrush
(Boldoschoenus compactus Hoffm.) and clubrush (B. maritimus Palla) are
sedge
weeds. The stalk is 85 cm tall and
triangular at the base. The leaf is long (70 cm)
narrow
and rough. The mature seed is small and dormant and is shed long before
the early rice is
harvested. Most of the seeds (up to 50 80 percent) over winter on check
surfaces then
germinate and produce
shoots in the spring when temperatures stabilize about 20°C and soil
moisture
approaches field capacity. Seedlings may even grow through a thin sheet
of water
about 1 2 cm. In the soil the
seed
remains viable for about 5 8 years. Both forms propagate by seed and by
tuber.
During one season each
tuber lying at a
depth of 11 15 cm produces from 10 to 47 new tubers
and in a year old grassland
up to 11 tubers. Tuberization occurs
primarily within the 2 10 cm layer of soil. In old riceland the number of tubers
within the depth of the
plow line may sometimes be as high as 1 000 2 000 tubers per sq m.
Tubers that
are buried at a depth of 20 23 cm for more than 9 years lose about 70
75
percent of their viability. Drying and freezing of the soil in old
riceland
markedly reduces the viability of propagules within the top soil.
Drying of the
soil (i.e. soil moisture under 14 percent) is fatal to tubers.
Spikerush
(Junceilus
serotinus Rottd.) is another persistent weed of the sedge family. The
triangular culm is about 1 m tall. It propagates by seed and by
rootstock. The
seed s dormancy and germination rates are about the same as in bulrush
seed.
Propagation is however usually vegetative through the rootstock. One
fruit
bearing organ produces up to 47 new cord like rhizomes in one season.
The
rhizomes are spaced at 3 to 20 cm apart and sit at the end of the old
rootstock. Freezing and drying of soil is lethal only to the surface
confined
rhizomes.
Common
cattail also mace
reed and narrow leaf
cattail are perennial weeds with a thick
creeping rootstocks buried at a depth of 5 10 cm. These
weeds have a 2
cm and a 0.5 1.0 cm broad leaf
respectively. Both weeds propagate by seed and by
rootstock. The small
sized seeds have a pappus and
are
grouped into cylindrical inflorescences
each containing up to 4 50 000 seeds. The seed germination
rate is about
100 percent in the year when the plant flowers. The seed produces
shoots at
temperatures no lower than 20°C in overwet soils
or fields with a thin water layer. Draining
of fields and drying of the soil kills the young plants. The weed
infests
mostly irrigation and drainage ditches
and newly developed rice lands
it
also thrives where cultural practices are poor.
Common
water
plantain (Alisma plantago aquatica var. maritima L.) is a perennial
weed that
infests rice fields in the Ukraine
Northern Caucasus Kazakhstan
and
Uzbekistan. Oriental water plantain (A. plantago asiatica) is a weed
that
causes problems in the Far East rice lands. It is a prolific plant that
propagates by seed and by tubers. Its maturity period is shorter than
that of
rice. The matured seed shatters and thus infests rice soils. One plants
is able
to produce anywhere from 15 000 20 000 and more achenes with a high
seedling
vigour. The seed germinates rapidly both in soils with moisture that is
close
to field capacity and
in submerged soils
with a floodwater temperature of 15 18°C. From the 1 cm layer of
submerged
soil water plantain
emerges shortly
after rice and completes with the rice seedlings for strength and
becomes
robust until the rice row stand close. The competition is particularly
vigorous
where the stands of crop are thin. Weed shoots develop from the buds
that sit
on the propagative tubers and
soon
appear to form leaves (in June and early July) that float on the
floodwater
surface shading and
suppressing the
young rice.
When buried
in
wet soil water
plantain propagules with
auxiliary buds can remain viable indefinitely
and are able to withstand heavy frosts. Even a mild frost however
can kill tubers when they are brought to the surface
during soil
cultivation. Smoothing underwater check surfaces following land
preparation
operations during the summer is considered an effective means of
controlling
water plantain.
Pickerel
weed
(Monochoria korsakovi Regal et Meack.) is an annual broadleaf weed that
can
survive in deep water. Pickerel weed usually infests rice fields and
irrigation
and drainage ditches. It is common in the far eastern rice producing
areas and
is a major weed where rice is shallowly seeded. Outbreaks of Monochoria
have
been recently reported in the Northern Caucasus – particularly in the
Kuban
delta ricelands.
The mature
plant
is 50 60 cm tall and
has a succulent
stem with thick broad
leaves. It
propagates by seed which
is enclosed in
a ball with a large pericarp. One Monochoria plant produces up to 20
000 seeds.
The mature seed germinates well in a soil with moisture close to field
capacity or in
flooded soil. The young
weed plant usually emerges in rice fields from mid June to early July.
The weed
is susceptible to shade. A good rice stand will suppress Monochoria in
that a
large number of the plants will die for lack of daylight. Most of the
remaining
plants (up to 95 percent) fail to produce inflorescence and therefore
do not flower. The weed
however thrives
in thin stands and then competes
vigorously with rice thus
reducing grain
yields. An efficient means of controlling Monochoria is to sow rice
early and
deep thus
permitting seedlings to be
obtained using naturally stored moisture. An additional means of
combatting the
weed is to level the fallow fields when they are under water.
Arrowhead
or duck potato (Sagittaria
trifolia L.) is a perennial plant with arrow shaped leaves. It
propagates by
seed and tuber forming stolons at depths ranging from 6 9 to 15 cm.
These are
underground shoots bearing about 8 tubers at each end. The tuber has a
crown
bud from which a seedling can develop earlier than from the seed
itself. At
soil depths of 20 25 cm the
tubers
remain viable for about a year or so. Drying of the soils kills tubers while a layer of water
stimulates the tuber
developing seedling which
can survive in
deep water and can break surface through depths of up to 50 cm. The
small sized
seed remains viable for about 5 years.
Acquatic weeds
Acquatic
weeds
include both the annuals and perennials
which can grow and bear fruit while immersed or floating on the water
surface. Some of
these weeds propagate by seed (chara and naiad)
others both vegetatively and by seed (pondweeds). Drying
of the soil is
harmful to all the weeds under this group.
Chara and
naiad
are annual weed plants 15
20 cm tall
that propagate by seed. They infest mostly the irrigation canals and
rice field
areas around turnouts. Drying of the fields for 2 3 days kills the
weeds.
Clasping
leaf
pondweed floating
pondweed and common
pondweed are perennials that
propagate both by seed and
vegetatively.
The shallow rooted rhizomes are able to easily break from the soil and
are
dispersed by flowing water. The weeds are unable to tolerate dry
conditions and
therefore infest primarily irrigation and drainage facilities as well as fields where
rice is grown
continuously. The economic losses attributable to these weeds are
large. They
infest waterways thus
greatly reducing
the water carrying capacity of the delivery canals by raising the water
level
in the drainage ditches. This in
turn causes the
water table in the non
irrigated downstream lands to rise
thus
injuring or
sometimes killing the
dryland crops grown there. Proper choice of rotational crops can
effectively
control these weeds.
Floating weeds
Thrive
in rice fields and
drainage and irrigation ditches. This group includes ninebark duckweed or duck s meat horned pondweed and many others. These
weeds are mostly
annual and propagate by seed.
Algae
Are lower
plants
several unicellular and multicellular forms of which commonly infest
rice fields.
When temperatures are high algae
of
various sizes and shapes rapidly develop colonies in the water (usually
in mid
May and June). One such algae is diatom which is the first to appear.
Others
are green algae blue
green algae and
brown algae. All these algae frequently form scum that deposits a dirty
film on
the emerging rice seedlings which
retards and frequently prevents further growth of the young rice
plants. Algae
scum is most harmful during emergence of the rice plants.
Weed Control Practices
Effective
systems of weed control combine preventive
mechanical cultural
and chemical
methods. Nonchemical methods include several or all of the following
practices using
weed free seed rice crop
rotations seedbed
preparation and land levelling selecting
the proper methods of seeding and
water and fertilizer management. Chemical methods are based on the use
of
herbicides that effectively control weeds in rice if applied properly
and
timely.
Nonchemical Weed Control
Weed
control
practices differ depending on the species and amount of weeds the structure of cropped
acreage in the
rotation the
availability of irrigation
water drainage
conditions in the rice
field and rice
varieties.
The
nonchemical practices can be
preventive mechanical
and cultural.
Proper combination of some or all of such practices will provide an
effective
weed control system.
Practices
that
prevent weed infestations or their spread in clean fields include the
use of
high quality seed rice that is free of weed seed
irrigation with water that is free of weed
seeds and other weed propagules and
cultivation with clean equipment.
Plowing disking
harrowing rotary
tilling or
combinations of these mechanical methods are used to prepare rice fields seedbed and eliminate
young weeds. In new
ricelands presowing
tillage of fall
plowed fields or spring plowing is done several days before seeding to
level
the check surfaces and make a fine tilth in the top layer (8 10 cm).
One of the
main goals of all methods of seedbed preparation is to eliminate all
weed
growth up to the time of seeding. Deep plowing in the fall (up to 20 25
cm)
with inversion of the soil layer to turn down the topsoil infested with
weed
seeds and
subsequent tilling in the spring
without inversion (subsoiling or chiseling) so as not to bring the
seeds to the
surface is a good practice to control barnyard grass and other
gramineous
weeds. The method chosen depends on type of soil
soil condition (mellowness)
other crops in rotation
the method of seeding
climate and the kinds of weed present.
Primary cultivation usually provides good conditions for weed seed
germination
and emergence and
subsequent cultivation
eliminates young weeds and conserves soil moisture. Old weeds that may
survive
on incomplete seedbeds are not so easy to control
therefore thorough preparation is important.
In the
major
rice growing areas the
old riceland is
harrowed late in March or in April to bring up barnyard grass. The rice
fields
are then disked and harrowed again to eliminate young weeds. If the
spring is
dry the old rice
fields are flushed one
or two times to provoke weed emergence 6 to10 days before weed control
cultivations. The number of presowing soil cultivations needed to
control
barnyard grass depends on how compact the topsoil is.
The seeding
method influences weed problems. The depth of tillage
regardless of implements used
should not exceed 5 6 cm in the field where
rice is to be drilled and
is unlimited
in these areas where the rice is broadcast onto the dry ground or in
water.
Time intervals between weed control cultivations and between seeding
the rice
and flooding the soil should be minimized. If this condition is
satisfied the layer
of water will prevent the emergence
of the barnyard grass whose seeds are only 2 cm deep in the soil.
Firming the
soil with a roller packer is a good way to bring up weed grasses due to
the
capillary rise of water to the topsoil
usually infested with weed seeds. On the average the rate of weed emergence
per square meter
on ground that has been firmed is twice that on unpacked ground. The
young
weeds that emerge after soil firming are easily eliminated by proper
cultivations. However the
barnyard grass
that emerges along with the drilled or dry seeded rice is difficult to
control
by cultural or mechanical methods. Water seeding reduces the growth of
barnyard
grass and other weed grasses during rice emergence. Herbicides are
essential
for controlling annual grasses that infest dry seeded rice and other weeds that
infest water seeded rice
such as the aquatic weeds and sedge.
Pest Profile and
Integrated Pest Management in Aromatic Rices
Introduction
Diseases
and pests attacking
normal rice cultivars also attack aromatic rices
only their relative importance may vary.
Diseases and pests which
are favoured by
late maturity (lower temperature)
dense
crop canopy and/or low nitrogen are more prevalent in aromatic rices
because of
their long duration and tall stature. Many aromatic rice varieties are
in
cultivation in their native areas since ages. Their nitrogen
requirement is
very low. They have become adapted and show less susceptibility to
different
diseases and pests in their native areas of cultivation. However some of the improved high
yielding aromatic
rice varieties an highly susceptible to diseases and pests like neck
blast sheath rot
sheath bight yellow
stem
borer white backed
plant hopper
(WBPH) brown plant
hopper (BPH) leaf
folders etc. Even traditional varieties
may suffer severaly once they are cultivated beyond their native areas.
There
is hardly any disease or pest attack on Tapovan basmati in village
Tapovan
areas (Tehri Uttaranchal).
However same
variety was severaly attacked by neck
blast and sheath rot when grown in plains. This paper reviews the
disease and
pest profile and discusses the importance of integrated pests
management (IPM)
in aromatic rices.
Diseases
Since
aromatic
rices are grown under both irrigated and rainfed ecosystems which
include
lowland upland and
high altitude
ecologies most of
the diseases are
reported from one or other areas. The most destructive diseases on
aromatic
rices are neck blast sheath
rot sheath blight
bacterial blight and brown spot. These and some other less
important
diseases are discussed in following section
Brown Spot
Helminthosporiosis
or brown spot disease of rice caused
by
Cochliobolus miyabeanus (Ito & Kuribayashi) Drechseler
(anamorph Bipolaris
oryzae (Breda de Haan) Shoemaker)
is one
of the most important diseases of the traditional aromatic rice more so under rainfed
conditions. Disease
appears as small oval or circular
dark
brown spots on leaves and glumes (Fig. 1). Spots are relatively evenly
distributed on the leaf surface. The disease is primarily seedborne however
secondary spread is rapid under favourable environment.
Disease is
aggravated by poor fertility conditions like low nitrogen phosphorus and potassium.
Due to lodging
problem in tall aromatic rice varieties
low dosage of nitrogen is applied. This results in high
incidence of
brown spot. Proper application of nitrogen
particularly in slow release form
suppresses disease development. However
one must be careful as high N may aggravate lodging
problem. Disease can
be managed by seed treatment followed
by
foliar spray of fungicides like mancozeb carboxin
bitertanol etc. Application of Si also reduces disease
intensity.
Biocontrol agents like Bacillus subtilis
applied through seed
soil or
foliar spray have been found to be effective. A number of aromatic rice
land
races/germplasms have been identified as resistant under natural
condition.
However among the
improved aromatic rice
varieties only Pusa
Basmati– 1 is
reported to be resistant.
Sheath Blight Complex
In rice
sheath
blight complex three
species of
Rhizoctonia R.
solani (teleomorph Thanetephorus
cucumeris) R.
oryzae (teleomorph Waitea
circinata) and R. oryzae sativae
(teleomorph Ceratobasidium
oryzae
sativae) are
involved. Rhizoctonia
solani inciting
sheath blight is
the most widely distributed species on rice.
First symptoms are greenish gray spots that develop on leaf sheath near
the
waterline. The elliptical or oval spots enlarge to 2 to 3 cm and
coalesce with
each other Figure (1). Disease may spread to upper sheath and
occasionally to
leaves. Losses may vary depending upon the time of appearance of the
disease.
Rhizoctonia solani has got very wide host range. However based primarily on the
astomosis
behaviour it has
been subdivided into 13
intra specific groups [an astomosis groups (AGs) and sub groups].
However all the
isolates of R. solani obtained from
rice belong to AG 1 IA and only isolates from AG 1 IA and AG 1IB are
capable of
producing typical symptom of rice sheath blight. Isolates from other
groups
were either non pathogenic or induced hypersensitive/resistant reaction
on
rice. However rice
isolates of R. solani
exhibit a wide variation in their morphological and virulence
characteristics
even if they are obtained from same field. Disease is favoured by high
N and P high plant
density and dense canopy. High yielding
dwarf broad leaf N and P responsive
varieties like Pusa
Basmati 1 are particularly susceptible to sheath blight. Nitrogen
increases
sheath blight essentially via indirect effects
increased tissue contacts in the canopy and higher leaf
wetness. In
addition to dosage time
of application
of nitrogen also affects sheath blight development. High K disfavours
disease.
There is a
lack
of resistance against sheath blight. However
some of the varieties/lines of aromatic rices have shown
reasonably good
degree of tolerance (U.S. Singh R.K.
Singh and G.S. Khush personal
observation). Crop rotation if
followed
properly could be
one of the effective
methods in keeping the soil population of rice isolates in check.
Balanced
application of NPK spray
of borax and
sulphates of Zn Cu
and Fe reduce sheath blight incidence. A
number of fungicides like propiconazole
pencyuron diclonazine flutolanil
mancozeb iprodione carbendazim are effective
against the
disease. New generation compound
acibenzolar S methyle
is reported
to reduce sheath blight severity when applied through soil or as spray
on
plants by inducing
plant defense
mechanism. A number of biocontrol agents like Pseudomonas fluorescens Bacillus sp
Trichoderma virens or T. harzianum alone or in combination
with organic
manure (Gliricidia maculata leaves) have been found effective in
reducing the
sheath blight infection under field conditions. Trichoderma harzianum
is an
efficient mycoparasite of R. solani. Preliminary studies have shown
that rice
wheat rotation which
is the most popular
in northern India does not favour sheath blight development in spite of
the
fact that wheat is susceptible to rice isolates of R. solani. However summer rice
maize or mentha do favour sheath blight.
Blast
Rice blast
caused by Magnaporthe grisea is a serious problem in aromatic rices
even under
low land irrigated system because of the long duration of crop. It is
most
serious problem in aromatic rises in Iran
Pakistan and India. In 1964
neck
blast epidemic was experienced in Basmati rices in Punjab province of
Pakistan.
During 1989 blast
epidemic in Basmati in
Haryana (India) resulted in loss of Rs. 110 million. Blast epidemic in
Kalanamak for two consecutive years
1998
and 1999 resulted
in sharp decline in
area under this variety in its native belt i.e. districts
Siddharthanagar Basti
Gorakhpur etc.
Blast has
two
phases leaf blast
and panicle blast.
Leaf blast is characterized by elliptical or spindle shaped lesions
with
whitish gray or greenish centre and brown or purple margins with yellow
halo.
Panicle blast which
is more
damaging appears as
a dark necrotic
lesion covering partially or completely around the panicle base or
secondary
branches. It may lead to breaking of panicles resulting in few or no
grain
setting. At the time of grain filling in aromatic rices temperature is
comparatively low which
favours panicle
blast development. Disease is favoured by high nitrogen. Soils with
poor silica
availability are blast conducive. In most parts of the world population
of
pathogen is reported to be clonal. However
in Himalayan hills population
structure of M. grisea exhibits high diversity in rice strains. Some
evidence
suggest recombination of rice and non rice infecting strains in Indian
Himalayas as a cause for this high diversity. In view of this
information there
is urgent need to analyze variability
in M. grisea population affecting late maturing aromatic rices grown in
Himalayan foothills. It may have lot of bearing on blast management
particularly
on resistance breeding.
A number of
effective fungicides like carbendazim
carpropamid tricyclazole pyroquilone
ediphenphos etc. are available against rice blast. In
aromatic rices
they are being used widely by the farmers. New generation chemicals
like
tricyclazoles carpropamid
etc. are
environmentally safe and provide good protection. Rather than being
directly
fungitoxic these chemicals act as antipenetrants by blocking melanin
biosynthesis in appressoria. Some of the biocontrol agents like
Pseudomonas
fluorescens Bacillus
sp. and mixed
formulation of Pseudomonas fluorescens + Trichoderma harzianum have
been found
effective against the disease. Application of silica fertilizers
reduces blast
incidence. Host resistance is the most effective method for the
management of
rice blast (Table 1). Unfortunately
most
of the popular varieties of aromatic rices are susceptible to neck
blast.
Nevertheless a wide
variation in reaction
towards neck blast was noticed in different Indian germplasm/land races
of
aromatic rices.
Sheath Rot
Sheath rot
caused by Sarocladium oryzae (Sawada) W. Gams & Hawksw which was considered only
a minor disease
till a few years ago has
now attained
the status of a major disease. It is primarily because of the
introduction of
some of the high yielding varieties. It might increase further with the
popularization of the hybrid varieties. Typical symptoms are oblong to
irregular brown to gray lesions on boot leaf sheath near panicle.
Lesions may
coalesce covering the entire sheath. Disease is highly damaging as it
infects
boot leaf sheath and under
severe
condition it may
totally inhibit panicle
emergence. Burning of the infected stables
planting of the tolerant varieties
spray of fungicide like carbendazim at tillering and boot
leaf stage and
biocontrol agents are some of the methods recommended for the disease
management. A wide variation was observed in natural incidence of
sheath rot in
different germplasm/land races of Indian aromatic rices (U.S. Singh.
R.K. Singh
and G.S. Khush personal
observation).
Early planted rice crops could escape disease incidence.
False Smut
Like sheath
rot false smut
caused by Ustilaginoidea
virens is another disease which has gained importance only during the
last few
years with the introduction of some of the high yielding varieties.
Infected
grains are transformed into yellow greenish or greenish black velvety
looking
spore balls. Incidence of the disease is likely to increase with the
popularization of hybrid varieties. Disease is favoured by high
nitrogen.
Sanitation practice like manual removal of sclerotia before harvesting proper dose of nitrogen and spray of fungicides
like foltaf mancozeb
etc. are some of the recommended
management practices.
Foot Root
Bakanae or
foot
rot a seed borne
disease is caused
by Gibberella fugikuroi
(Anamorph Fusarium
moniliforme).
Infected seedlings/plants are elongated nearly twice the height of the
normal
plants with thin yellow green leaves. Elongated plants die. Infected
plants
that survive until maturity bear only partially filled grains or empty
panicles. High nitrogen and temperature range of 30 to 35°C favour the
disease.
This is one of the major diseases in Basmati belts of Haryana (India)
and
Punjab (India and Pakistan). In 1991
most of the Basmati fields in Punjab province of Pakistan
were badly
affected by this disease. Outbreaks of this disease were observed in
Haryana
during 1989 1990
and 1992. Foot rot can
be effectively controlled by seed dressing with fungicide like
carbendazim.
Stem Rot
Stem rot
caused
by Magnaporthe salvini (sclerotial stage Sclerotium oryzae is endemic
in
eastern U.P. Infection starts near the waterline as blackish dark
irregular
lesions on the outer leaf sheath and gradually enlarges. Eventually
fungus
penetrates into culm and weakens the stem leading to lodging. The
disease is
favoured by high nitrogen while
K and Si
application reduce disease incidence. Application of balanced fertilizer burning of stubble after
harvest avoidance
of waterlogging for long period and
planting of moderately resistant varieties are some of the recommended
methods
for the disease management. Some of the aromatic rice varieties are
reported to
be resistant to stem rot.
Narrow Brown Leaf Spot
This
disease is
caused by Cercospora oryzae. Incidence of the disease has increased in
recent
past particularly in Bijnore (U.P.) and
Dehradun (Uttaranchal).
The disease is characterized by small
narrow elongated
dark brown spots
spread uniformly over the leaf surface. Work is in progress to develop
disease
resistant varieties. Some of the non aromatic resistant varieties like
Mahssuri Bhawani IR 26
IR 28 IR
29 and IR 30 may serve
as donors.
Bacterial Blight
This
disease is
caused by bacterium Xanthomonas
campestris pv. oryzae (Ishiyama) Dye. Disease may appear both in
nursery
(Kresek phase) as well as in field. Kresek phase is characterized by
wilting of
seedlings. In mature plants lesions
usually start near the leaf tip or margins or both and extend down the
outer
edges. Young lesions are pale green to grayish green
later turning yellow to gray necrotic.
Lesions may extend to entire leaf length (Figure 1). Disease is more
serious
under irrigated conditions. Bacterial blight is a widely distributed
and
devastating disease of rice. Some of the aromatic rice cultivars like
Pusa
Basmati 1 are highly susceptible to bacterial blight. It is favoured by
high N.
Planting of resistant cultivars is the best method of disease
management. A
number of resistant varieties are available among non aromatic rices.
Among
aromatic rices HBC 19 Pakistani
Basmati Ghanal and
IET 9691 showed
resistance to bacterial blight. Proper use of nitrogen and avoidance of
shade
and water stagnation in field help keeping the diseases in check.
Grain Discolouration
It is
characterized by darkening of glumes of spikelets
brown to black including
rotten glumes. Disease intensity
ranges from sporadic discol ouration to discolouration of entire
glumes. A
number of fungi viz. sarocladium oryzae
cochliobolus miyabeanus Alternaria
alternata Magnaporthe
salvini M. grisea
etc. are reported to be involved in
grain discolouration. High rainfall at the time of maturity favours
development
of grain discolouration.
Insect Pests
Insect
pests
pose serious threat to cultivation of rice in almost all regions of the
world
where rice is grown. More than 800 insects species have been recorded
damaging
rice in one way or another although
majority of them are of little importance. In a particular area insect pests attacking
aromatic rice are the
same as those prevalent on non aromatic rices. Nevertheless mainly due to long duration tall stature and dense
canopy the aromatic
rice cultivars are more
susceptible to insect infestation as compared to non aromatic rice due
to which
the farmers in many traditionally aromatic rice belt have given up its
cultivation. In India the
aromatic rice
is damaged seriously by yellow stem borer
Scripophaga incertulas Walker
leaf folder Cnaphalocrosis
medinalis Guenee white
backed plant
hopper Sogatella
furcifera and brown
plant hopper Nilaparvata
lugens.
Yellow Stem Borer Scripophaga
incertulas (Walker) (Lepidoptera
Pyralidae)
The most
serious
insect pest of Basmati rice in the entire northern Indian belt is
yellow stem
borer. Studies conducted in Punjab over five years revealed that non
protection
of Basmati 385 may result in 80 97% white ears in crop due to stem
borers.
Yellow stem borer epidemic was recorded in Basmati belt of Haryana and
Punjab
during 1998 where 50% incidence of white head was noticed. The yellow
stem
borer lays eggs near the tip of leaf blade
which are covered with buff coloured hairs derived from
anal tuft of
female moth. One female moth lays an average of 2 to 3 clusters of egg each containing about 60
to 100 eggs. About a
week after hatching the
larvae from the
leaf sheath bore into the stem and staying in the pith
feed on the inner surface of the walls. Such
feeding often results in severing of the apical parts of the plants
from the
base. When this kind of damage occurs during vegetative stage of the
plant central leaf
does not unfold turns
brown and dries off although
the lower leaves remain green and healthy. This condition
is called dead
heart . The affected tillers dry out
without bearing panicles. After panicle initiation
severing of the growing plant parts from the
base result in the drying of the panicles
which may not emerge at all
and those
that have already emerged do not produce grains. This condition is
known
as white ear head .
The borer remain active
in the field almost from nursery stage to crop maturity. However they cause more injury to
the plant from the
middle to later part of the crop growth. It has been observed that
among the
three stages of crop growth maximum
tillering stage registers highest infestation
followed by flowering and early tilering stages. It has
also been noted
that the variety having more tillers per hill suffer more from yellow
stem
borer. The economic injury threshold for dead heart and white head are
reported
to be 5.7 12 and 9.4 14.7% respectively.
These values seem to be quite high value aromatic rices. It may be
revised as 5
and 3% respectively for dead heart and white
head.
Hoppers
Hopper burn caused either by white
backed plant hopper
(WBPH) or brown plant hopper (BPH)
is
quite common to aromatic rices. They may result in serious losses. In
recent
years incidence of
green leaf hopper is
on increase in Basmati in Uttaranchal Tara.
1.
Brown planthopper Nilaparvata
lugens (Stal.) (Homoptera Delphacidae)
The nymphs
and
adults of brown plant hopper suck the phloem sap from the basal portion
of the
plant which result
in yellowing and
wilting of plants and
finally leading to
hopper burn. The eggs of BPH are usually laid in groups in the tissues
of the
lower part of rice plant mainly
in the
leaf sheath but at
times also in the
leaf blades. One female may lay
400 500 eggs which
hatch in 7 10 days.
In the Basmati belts the
population of
this insect remains very high in September October.
2.
White backed planthopper Sogatella
furcifera (Horvath) (Homoptera
Delphacidae)
In U.P. and
Uttaranchal white
backed planthopper is
more common than BPH. It lays eggs in masses in the leaf sheath tissues
of the
plant which hatch
in 3 14 days. During
the period of feeding variety
and stages
of crop also affect the symptoms. If the attack is before heading stage lower leaves
followed gradually by the upper leaves
turn yellow to bronze. There are stunting and reduction in
the number of
productive tillers. When the damage is in the panicle formation stage the number of grains and
panicle length
decrease considerably. There is adverse effect on the ripening when
WBPH
attacks during maturation period. The flag leaf and panicle are
aggressively
attacked by nymphs and adults the
population of which remain high from early September to mid October.
Rice
Leaf Folder Cnaphalocrocis
medinalis (Guenee)
(Lepidoptera Pyralidae)
The rice
leaf
folders belonging to Cnaphalocrocis and Marasmia
have recently acquired the pest status in
rice. However Cnaphalocrocis
medinalis
has become a major pest of rice causing moderate to severe damage in
most of
the rice growing regions. In Bihar
the
infestation of this insect reached to 78.1% leading to 90% yield loss
in
scented rice. Similarly untreated
fields
of Basmati rice in Haryana and adjoining areas
have been reported to suffer 30 80% loss in yield due to
attack of leaf
folder which may cause up to 28.5% leaf damage after increasing its
population
to 20 larvae/hill. Unbalanced use of fertilizers
especially excessive application of
nitrogenous fertilizers seems
to be one
of the important factors of increasing menace of leaf folders.
The eggs
are
laid in batches of 10 to 12 arranged linearly along the middle on
either
surface of the leaves. One female lays approximately 100 eggs. The
damage is
caused by caterpillars which
fold the
leaves longitudinally by fastening margins with silken threads and
feeding
inside the fold. During feeding the
larvae of C.medinalis sit along the length of the leaf blade and scrape
out the
soft tissues between vascular bundles longitudinally. As a result only
bundle
unit bundle sheath sclerenchyma
the aboxial epidermis and the cuticle are left intact. In
severely
attacked condition the
crop gives scorched
whitish appearance of infested plants and consequently of leaves. They
create a
leaf tube during the later stages of feeding. Several natural enemies
viz. Cotesia sp.
Trichogramms sp. Bracon
sp. etc.
have been found parasitizing leaf folder larvae in the field and
keeping the
population below ET level.
Rice
Hispa Dicladispa
armigera (Olivier)
(Coleoptera Chrysomelidae)
It is
widely
distributed in Burma China India
Nepal Pakistan
and Sumatra.
Female beetle lay eggs singly near the tip of the leaf blade and
partially
inserted in the mesophyll tissue of the ventral surface of the leaf.
One female
lays an average of 55 eggs which
hatch
in 3 5 days. The grub mines the leaf between epidermis producing
irregular longitudinal
white blotches. The adults feed
on all portion of leaf producing white parallel streaks along the mid
rib of
the leaf leaving only the lower epidermis. The damage by this insect is
restricted in early stage of the crop.
Integrated Pest Management
Rice ranks
second in consumption of chemical pesticides
particularly the insecticides. Their indiscriminate use
has affected the
ecology adversely. In addition to environmental pollution and health
hazards this has
led to resurgence of
pests and pesticide
resistance leading
to failure of chemical protection and heavy loss to crop. Serious
outbreak of
hopper burn due to WBPH was observed in Pusa Basmati 1 fields heavily
applied
with phorate granule in schedule based operation during 2001 at
Pantnagar. With
the development of several alternate methods of insect control now it
is being
realized that to tackle the insect pest problems in aromatic rice
safely more
emphasis should be given on the use of resistant varieties manipulation of agronomic
practices conservation
and enhancement of natural
enemies and need based application of safe insecticide molecules.
Water Management
Practices for Rice
In modern rice culture water management is of
great importance as it
stimulates better crop growth and higher grain production. Water
management
involves the manipulation of the hydrologic cycle at various stages to
make
water available when
necessary to remove
it when there is an excess of it
and to improve its quality if
required.
It thus involves irrigation drainage
and
the conservation of water. A major factor underlying stagnation in the
yield of
the rice crop appears to be poor water management.
In the
states of
Tamil Nadu Jammu
and Kashmir Punjab
and Haryana where
more than 85 per cent of the area is
irrigated the yield
per hectare are
relatively high. The states which
have
the poorest irrigation have
the lowest
yields.
Irrigation
stabilizes yield. It has been stated that the rainfall during the rainy
season
in most of the rice growing states in India is generally sufficient for
rice
cultivation but it
is erratic in
time space and
quantity. This situation
either causes drought or floods both of which adversely affect the
yield of
this crop. With the provision of irrigation facilities
the adverse effects of drought can be
avoided. Irrigation dams help to control floods and regulate water
supply besides
stabilizing yields. Statistics show
that in Asia during the last 10 years
about 10 per cent of the cultivated area in each year has
been affected
by floods or drought.
It has been
proved that not only can irrigation ad drainage help to stabilize the
yield of
the rice crop but
well managed water can
also increase its yields. Under scientific management
the required quantity of water is made
available to the crop when
needed.
Experiments have demonstrated that a 100 per cent increase in yield may
be
realized with no other changes in agro technical methods than
controlled
irrigation with
proper management.
Table
1. States with poorest
irrigation have the lowest yield
Precise
data are
available on all aspects of water management in our country. These
aspects are
reviewed in the following sections
The effect of land submergence on the growth and yield of
rice
Studies
have
been undertaken by many workers to determine the effect of land
submergence on
the growth and yield of rice.
The depth of submergence
The
advantages
of land submergence led the workers to initiate work to know the
optimum depth
of submergence for obtaining the maximum yield.
Ganguli
working
in Assam reported that the water level of 7.62 cm throughout the growth
period
of rice was the best whereas
Pillai
inferred that the maintenance of 5.08 cm of standing water with frequent changes with fresh water resulted
in high rice
production.
In the
black soils
of Siruguppa Mysore
submergence under 5
cm deep water resulted in the highest grain and straw yield obtained
under the
following three treatments
1.5
cm submergence
2.saturation
to hair cracking and
3.flowing
water.
A thin
layer of
water is sufficient to maximise the yield of rice
no additional advantage occurs from very deep
submergence which
entails only wastage
of water.
Bhatia
and Dastane found that a
depth range up to 0 4 cm seems to be the optimum for high yielding
dwarf rice.
The above
workers further added that for dwarf rice varieties
deeper submergence may be harmful
as shown above. Pande and Mitra (1970) found
that the grain yield of rice was better under submergence than under
mere
saturation during summer and spring and also that the crop under
shallow
submergence (5 ± 3 cm) gave as good a yield as deep submergence (10 ± 3
cm).
Ghildyal
and
Jana on the basis
of pot
experiments observed
in general that the
highest yield was obtained during a cool and dry season
with 0 3 cm of water.
The results
of
the experiments conducted recently under the All India Co ordinated
Scheme for
Research on Water Management and Salinity have shown that the field
submergence
under water 5 to 10 cm deep does not produce any significant difference
in the
yield and hence shallow submergence up to
5 cm is economical.
From an
experiment conducted at Bhubaneswar on a sandy loam soil with a pH of
4.9 Sahu and Rout
reported that the lowland rice
( T 1242 ) gave the maximum yield when the soil was kept submerged
under 15 cm
of water. The yield was reduced by 26.4% under field capacity and by
29.2 at 75
per cent available moisture as compared with the yield under deep
continuous
submergence though
the efficiency per
unit of water used was higher from the first two treatments.
Nephade and
Ghildyal observed in a lateritic sandy clay loam soil with a pH of 5.1
at
Kharagpur that the yield of rice was higher under shallow flooding (3
cm) than
under deep flooding (15 cm). Chandra Mohan from Tamil Nadu reported
that among
the various depth of submergence the
5
cm depth of water proved in
general to be the
optimum depth of submergence for
getting the best yield.
According
to
Ghose et al. a
small quantity of water
used at shorter intervals was more beneficial to the rice crop than
larger
quantities at longer intervals.
The results
of
studies made at Kharagpur on a lateritic soil (pH 5.4
hydraulic conductivity
0.51 cm/hr
of low fertility 0.04% N
0.0055%
available P and 0.1% available K) under the co ordinated Project for
Research
on Water Management and Salinity show the monsoon season shallow submergence and
deep submergence were
as good as saturation for IR.
8 rice because of
the effect of rains low
evapourative demands. But during
summer shallow
submergence scored over
deep submergence or saturation.
The work
done at
Chakuli (sandy loam soil) Orissa
at
Siruguppa (heavy black soil with 50% clay). Mysore
and at Roorkee (alluvial soil)
Uttar Pradesh
under the Co ordinated Scheme showed that submergence up
to 5 and 10 cm
did not show any significant difference in yield and
therefore
submergence up to 5 cm only was economical.
The results
discussed above show that for tall rice varieties
a slightly higher depth of submergence may be
tolerated whereas
for new dwarf high
yielding rice varieties a
depth of 5 cm
is enough to get a good yield.
Effect of partial submergence
Since the
continuous submergence of the field involves a huge quantity of assured
water many workers
started experiment to
find out the critical period of land submergence for economizing on
water.
According
to
Singh et al. Ghosh
and Bhattacharya Sen
and Dutta
Vamadevan and Dastane
Chaudhury
and Pande tiller
initiation primordium
initiation and flowering are the
most critical stages. A shortage of water during these stages could
reduce
grain yield appreciably. Therefore
submergence at these stages should be practised. Further Ray and Pande emphasized
the point that the
flowering stage was the most critical period.
The data
revealed
that the highest grain yield at Chakuli was obtained when the soil
moisture was
maintained at saturation till tillering
followed by submergence under 5 cm of water till
harvesting (M1).
Continuous submergence (M8) did not show any additional advantage while continuous
saturation till flowering
brought about a reduction in yield.
At
Kharagpur the
highest grain yield was
obtained during kharif under the treatment in which saturation was
maintained
till tillering followed
by submergence
till harvesting (M1) whereas
during
rabi the treatment submergence till flowering followed by saturation
till harvesting
(M3) produced the
highest grain
yield though the
treatment saturation
till tillering followed by
submergence till harvesting (M1) also produced more or less similar
yield.
Continuous submergence required the greatest quantity of water without
any
additional benefit in terms of grain yield. The results of another
experiment
conducted using IR. 8
during kharif 1971 at Kharagpur
showed that submergence under 5±2 cm of water maintained
only during the
active vegetative and reproductive phases
and saturation during other phases produced the maximum
grain yield.
The result
of
the studies taken up at Siruguppa (Mysore) also reveal
in general that
tillering to flowering was the most
critical stage when the rice crop should not be subjected to any
moisture
stress.
Table
2.
The effect of moisture stress during different growth
stages on
the yield of rice
As already
stated in most cases the
shallow
submergence of the fields has been reported to be beneficial. However where the water table is
shallow even
shallow submergence may be avoided
meaning thereby that a reasonably good yield
of rice can be obtained by maintaining the rice field just moist (0 3
atm.) to
avoid cracking. A number of experiments at the Indian Agricultural
Research
Institute during kharif have also corroborated this result.
Mane working on rice variety NP. 130
reported that there was a good scope of economising on
irrigation water
in the rice fields by applying water at 0.2 or 0.5 atm. tension and not
going
in for continuous submergence.
Rao studied
the
influence of moisture regimes on the yield and yield components of the
rice
variety under the conditions of a shallow water table. The results are
presented in Table 3.
Table
3 The yield and yield
attributes as
affected by moisture
regimes
Neither the
grain yield nor any yield component was influenced significantly by
moisture
stress up to 0.3 atm. tensions where the water table was shallow. This
observation suggests that where the water table is shallow there is no need to
submerge the fields.
Recently Jha found a suitable water
management
practice for rice using
the varieties
maturing nearly in 115 to 120 days (viz.
Sabarmati and Jamuna ). He recommended
that with a much
less quantity of water (by scheduling irrigation at 0.3 atm. tension)
in the rice
fields as compared
with the conventional
practice of keeping the water standing in the rice fields a good yield of rice (even
better than that
from the latter practice) could be obtained by scheduling irrigation in
respect
of rice at 0 0.3 atm. tension but
supplementing the crop with a foliar spray of nitrogen (urea) potassium silicate and
ferrous sulphate (under
poor Fe status) and controlling weeds with a suitable herbicide. However caution must be exercised
to avoid stress
during critical stages such as active tillering and flowering. He was
of the
opinion that the applying of silicate maintained leaf turgidity and the
rest of
the nutrients compensated for the loss caused by slightly oxidized
condition
prevailing in the field because of scheduling irrigation at 0.3 atm.
tension.
The yield and the economics under each water regime are presented in
Table 4.
The data
presented in Table 4 clearly revealed that though there was an increase
in the
grain yield by about 4.75 quintals per ha
when set off against the extra cost of irrigation water there was a reduction in
the net return by
about Rs 185. Whereas the applying of a foliar spray of N in preference
to the
soil application of N120 P60 K40
under the moist regime it was possible to increase the
grain yield by
about 9 quintals/ha by incurring an additional expenditure of 80 rupees which resulted in an
additional net return of
Rs 433/ha. Likewise a foliar spray of different nutrients e.g. iron or silicon resulted in a significant
increase in the
grain yield and in a high net return per hectare over that resulting
from the
application of fertilizers to the soil.
Water Requirement of the Rice Crop
Earlier
studies
on the water requirement of the rice crop were directed towards
transpiration
ratios and were conducted mostly with plants grown in pots. This
procedure
reduced the significance of these studies. Dastane et al. reviewed the
work on
the water requirement of crops including
rice. According to them the
latest
definition of water requirement is
regardless of source
the quantity
of water needed to grow a rice crop under field conditions . This
definition
embraces evapotranspiration application
loss (percolation and seepage) and special needs (e.g. the leaching of
excess
salts and preparing the field). They reported that owing to the
difference in
the different components of water requirement
the water requirements of the same variety or crop may
differ widely
from place to place.
It seems
that
water requirement of the rice crop varies widely
depending upon the soil
climate
season varieties
and management
practices because
the above mentioned
components are the function of these entities.
Diseases and
Pests
of Rice and Their Control
The
importance
of insect pests is generally recognized
the damage they do is widespread and very evident but the loss of crop
caused by diseases
should not be overlooked or considered negligible. The crop is liable
to many
diseases any one of which may suddenly inflict widespread damage.
In
recent years the effect of
plant protection has significantly increased. Although average losses
in most
fields have been appreciably reduced due to adequate plant protection
measures losses in
individual rice
growing areas and fields from specific diseases and pests are at times
high and
markedly reduce that total grain output in the country.
Practical
plant
protection includes not only destructive measures
but also the use of resistant rice
varieties methods
that result in
unfavourable conditions for the development of injurious organisms and practices that
conserve useful
enthomofauna. Such protection also allows one to control economically
important
pests which rely on population thresholds by using
in the first place natural
limiting factors and
then other plant protection methods that
are consistent with economical
ecological and
toxicological
requirements.
Rice Diseases
Most of the
world s major rice diseases are known to occur in the Soviet Union.
Blast for one
is a major disease caused by the fungus Pyricularia oryzae
Cav. It
occurs in almost all rice producing areas and is the most noxious
disease of
rice. The fungus mostly attack the leaves and to a lesser extent the nodes and panicles.
The disease results
in both leaf blast and head blast. The latter condition is where the
panicles
frequently break over due to infection weakened structural tissues in
the panicle
and is sometimes known as rotten neck.
Atmospheric
moisture and temperature conditions are of primary importance in the
infection
and spread of the fungus that causes blast. Frequent rains heavy nightly dews high relative humidities
and temperature (18
20°C) favour wide scale outbreaks of the disease Rice plants under high
levels
of nitrogen fertilization are more susceptible to blast. The outbreaks
of
disease may be caused by use of susceptible varieties or uncleaned
seeds mixed
with the seeds of varieties consistently susceptible to blast. Blast is
heavier
on late sown than on early sown crops. The infection is persistent in
seeds on the stubble in straw and reed growths.
The average
losses in yield of the fungus affected plants account for 25 percent.
The
milling yield of head rice is decreased by about 23 25 per cent.
Treatment of
the rice crop infected with P. oryzae includes spraying with 0.4% zineb
solution (80 percent wettable powder) at a rate of 2.4 kg/ha or with rhizid P (50%
emulsible concentrate)
at a rate of 0.5 1.0 kg/ha in
terms of
the active ingredient. The rate of application is 200 1/ha. The
treatment of
the crop should be completed 20 days before harvesting.
Preventive
measures include early fall plowing
seeding with clean certified seed from the varieties
selected best for
that area s growing season the
application and uniform distribution of nitrogen fertilizer and seed dressing or
disinfecting with
coloured granosan M dusts at 0.04 kg (active substance) per ton of
seed.
Other rice
diseases such as
brown spot sclerotical
rot root rot and
bacterial disturbances are
rare and of less
economic significance.
Recommended
control and prevention practices against fungi and bacteria attacks
include the
removal of rice straw burning
of plant
residue deep fall
plowing with inversion
of the soil layer and
rotational
planting (with cultivated fallows and leguminous grasses). Seed
dressing with
coloured granosan M dusts (0.04 kg/ton
active substance) is mandatory.
General
symptoms
of rice diseases are abnormal plant growth and changing leaf colour. A
disturbance in plant development manifestes itself in retarded growth
and
excessive or reduced tillering. The stems and leaves may develop galls
or
cecidia streak
mozaic and necrotic
areas. The leaf may change its coloration from green to yellow green or
yellow
orange. Diseases are transmitted basically by suctorial insects. To
prevent the
spread of such diseases rice fields are treated with phosphororganic
substances
in the early stages of plant development to kill cicads (Cicadidae) insect vectors of virus
and micoplasma inhabiting
clumps of grasses particularly
barnyard grass.
White tip
disease of rice caused
by an
ectoparasitic foliar nematode
Aphelenchoides besseyi Christie
is another widespread noxious disease of rice.
The most
distinguishing symptom of white tip is the presence of leaves with
white tips
of 2.5 5 cm long. The tips of the developing leaves may be twisted and
wrinkled
and the flag leaf may be twisted and wrinkled and the flag leaf may be
twisted
near the panicle. The infected plants are generally stunted.
The
nematodes
are seed borne and
are spread from one
crop to the next in seed rice and stubble. They become active after
rice is
sown and migrate
towards the growing
point of the young rice plants where the nematode feed and reproduce.
Anywhere
from 8 to 13 generations can be reproduced during a growing season.
Feeding
injures the developing leaves and panicles before emergence. Later on the injuries are white necrotic leaf tips and
small sterile
panicles. Grain yields from diseased
plants are markedly reduces.
Several
methods
can be used to control white tip. Resistant seed varieties nematode free seed should
be used in
planting re cleaned
seed lots free from
shrunk and light weight seeds can be used for seeding. Infected rice
straw
should be removed from the fields and burnt. Fall plowing and rotations
also
help control or prevent the spread of white tip in rice.
Pests of Rice
Several
pests frequently
damage rice severely. Among them is the larva of Dioptera and
Orthoptera which
may cause serve injury by feeding on young rice plants
particularly in rice grown in saline soils.
Economically important population thresholds constitute 40 larvae per 1
sq. m.
The tadpole
shrimp Triops
(Apus) cancriformis
Schaft. although
not an insect is
also a pest of rice. The adult spherical
shield shaped shrimp is
about 3.0 3.5 cm long. The eggs are ball
shaped reddish
black and 0.4 mm in
diameter and are laid by the female shrimp in water or soil. This gives
the
eggs shelter for many years after water is withdrawn. In the spring 3 to 4 days after flooding
the field the eggs
hatch and the young larvae or
maggots as they are
commonly called emerge
to become fully grown adults in 14 15
days. The young larvae first feed on the organic matter
and within 8 9 days reach 7 10 mm in length.
They then migrate to the rice and cause severe injury by pruning the
young
roots and shoots. Germinating seeds lying on the soil surface become
easy
targets for the maggots. The tadpole shrimp survives for one generation and late in June it disappears.
Since the
immature stages are spent underwater among the rice roots most of the shrimps larvae
can be destroyed
by draining the fields and allowing them to dry for a day or two.
Appropriately
leveled checks timely
opened drainage
furrows and peripheral ditches are essential for rapid drainage.
Esteria
(lumnadia) Leptestheria
spp. a shellfish
is another aquatic pest of rice
its body is enclosed in a bivalve translucent shell and is 9 10 mm long and 4
5 mm broad in fully
developed specimens. It moves with the
use of its antennae and lays its eggs in a shell. Its white ball shaped
eggs
are 0.13 mm in diameter and dropped into water as they accumulate
within the
shell. The eggs settle on the soil surface
and may stay there for years. Three days after the field
is flooded the eggs
laid in the previous season
hatch and larvae
emerge.
Esteria
matures
within 8 to 10 days the
first 5 to 7 of
which are spent feeding on organic matter. Upon reaching maturity the full grown Esteria
quickly migrates to
the soil surface and begins to feed on the young rice plants. What
ensues is
the destruction of a significant number of these plants. The life cycle
of
Esteria is one generation and
it can be
found in rice fields until late June.
Draining
and
withholding water for 1 2 days controls larvae development by
disturbing its
life cycle thus
eliminating the risk of
injury to rice seedlings.
The caddis
fly (Trichoptera)
Limnophylus
stigma is an insect
pest of rice.
Several species of this numerous insect order are present in the Far
East and
Central Asia injuring rice severely in certain years. The 10 16 mm long
larva
is what inflicts damage on the rice plants. The larva lives in the
water
enclosed in a cigar shaped tube that it builds around its body from
minute
plant debris and trash. The tube size varies from 12 to 20 mm. The
larva holds
the tube fast on its body with its last body segment and moves about
with its
head and three pairs of thorax legs. The larvae migrate to rice fields
and feed
on rice seedlings thus
reducing the
density of plant stands.
Draining
the
field for 1 2 days or treating it with chlorinated lime at a rate of 10
12
kg/ha helps control the caddis fly.
The barley
leaf
miner Hydrellia
griseola Fall. is a
dangerous pest of young rice in the Far
East Northern
Caucasus and the
Ukraine. A grey fly 2.5 mm long the
miner usually infests rice fields in
April and in the Far East in May. Its white eggs
elliptical in shape and 0.6 mm long
are laid on the upper leaf surfaces and along
the veins of rice leaves that are afloat. Damage is done 2 3 days after
the
eggs hatch and the maggots appear. The miner maggots attack the leaves
and feed
on their parenchyma. This reduces the photosynthetic capacity of the
leaves and
consequently impairs the rice yield. The pale yellow maggots are
elliptical and
3.0 3.5 mm long. They pupate in the mines they have made in the leaves
and
develop pale brownish pupa. Within 6 9 days they emerge as flies. The
barley
leaf miner produces 3 4 generations and attacks all rice seedlings
regardless
of the date of seeding.
Lowering
the water or draining
the fields for 2 3 days or
treating
fields with a 20% emulsifiable methaphos at 0.2 0.4 kg/ha (active
ingredient)
provides reliable control of egg and larva population.
The rice
leaf
miner Hydrellia
griseola var. scapulasis
Loew is a
destructive pest of rice in
the Far East. The black flies are 3.3 3.8 mm long and lay eggs on the
leaf tip
tissue. They attack rice in June. The maggots are yellow green 4 6 mm long when hatched and feed within the leaf working their way towards
its base. The
larvae pupate on the top of the damaged leaf
which turns brown and lies prostrate on the water.
Infestation leads to
a reduction in yield. The rice leaf miner produces three generations of
which
the first two are most damaging to rice. Preventive measures include
adequate
weed control and proper water management.
The rice
midge Chirono mus
spp. is a
destructive pest of rice in the Far
East Northern
Caucasus and the
Ukraine. Only occasionally does the
insect infest rice in Central Asia. Light attracts the midge and can be
used to
determine when the midge is attacking the rice fields. Such attacks
usually
occur in April. The eggs laid
in
water hatch
yellowish translucent
larvae within 2 3 days. The
larvae first feed on organic matter and rice roots. During this time the injury to the rice is
insignificant. The
adult larvae 8 mm
long infest the
lower surface of leaves that are
afloat and feed on
the parenchyma. This
causes the leaves to wither and reduces yield. The rice midge produces
three
generations and damages all rice seedlings regardless of the date of
seeding.
It is most damaging when the rice plants are excessively flooded and
the leaves
stay afloat for a long time on the water surface. Lowering the water
level or
draining the rice fields for 2 3 days provides effective control of the
midge larvae.
Treatment of the fields with a 20% emulsifiable methafos at a rate of
0.2 0.3
kg/ha by aircraft sprayers is also effective on large larvae
population.
The shore
fly Ephydra
macellaria Egg. infests
rice in almost all rice growing
areas. The fly is 4 mm long. Its thorax and abdomen are metallic green its legs
reddish green. Its wings are large and translucent. It
lays about 80 to
90 eggs in the water covering rice checks. The larvae are what is
destructive
to rice as they are
adapted to live in
water. Where they feed on young rice roots. Such feeding results in the
withering and reduced rice plant stands. The larvae pupate where they
feed i.e. on roots
stems and leaves and
emerge as
flies within 8 to 12 days. The fly produces 3 4 generations. When
larvae
population counts are high withholding
water for a day or two may provide adequate control. Treatment of field
with
80% emulsifiable chlorophos powder at a rate of 0.8 1.6 kg/ha is also
effective
in controlling large larvae populations.
The rice
water
weevil Hydronomus
sinuaticollis
Fst. is found in
all rice growing areas
of the Far East and Central Asia. The adult weevil is black 4 5 mm long
and has two light spots on the elytra. The male water
weevil is smaller
than the female. In the post feeding stage the larvae overwinter in the
plowed
up soil at a depth of 5 8 cm. The larvae are milky white legless
and about 7 8 mm long when fully grown. They pupate in the
spring and emerge
as weevils in May or June. The
weevil feeds on germinating seeds and roots of young rice. Rice that is
sown
late is usually more susceptible to the weevil. Eggs are laid in the
root zone.
The hatched maggots live first in the plant
and later migrate to prune the roots. Infested plants
either die or grow
more slowly forming small panicles
with poorly set kernels. Rotations
disking the stubble in the spring
fall plowing and
seeding at
optimum dates help prevent and control the rice water weevil.
The rice
leaf
beetle Lema
suvorovi Jacobs var. oryzae
is a widespread and destructive pest in the Far East. The bugs 4 5 mm long
have blue elytra and yellow head and prodorsum. They feed
on rice
leaves. The female bug lays chains of 6 to 12 eggs on the upper surface
of the
leaf in late May and early June. The eggs hatch and larvae emerge which
feed on
leaves and in mid June when they complete feeding
they pupate and emerge as bugs 10 12 days
later. The rice leaf beetle produces two generations the first of which
is the
most damaging to rice. Bugs of the second generation spend the winter
in the
soil or in dry grass straw
and other
material that affords them shelter. In the spring
then
they infest primarily the weed plants. Proper weed control
and treatment
with 80% emulsifiable chlorofos at 0.8 1.6 kg/ha (in terms of active
ingredient) reduces the number of bugs in subsequent season.
The cereal
aphid Aphididae attacks rice in the
Northern Caucasus the
Ukraine
and Central Asia. Aphids are most destructive to rice sown
late in the
spring on soils deficient in nitrogen. Some species are winged others
wingless. The economically significant level of
infestation (population
threshold) is 1 2 aphids per square meter at leaf tube formation. The
appearance
of aphids in rice can be controlled by proper and timely weedings and
treatment
of fields with 20% emulsifiable methaphos at 0.2 0.3 kg/ha (active
substance).
Many other
species of insects and various other pests infest rice fields by
migrating to
rice from the leaves and weed growths. Feeding on rice is supplementary
for
most of them so if rice cultivation
practices are
adequate the
infestations seldom cause
enough damage to reach economically significant levels.
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