Everything you need to learn about rice cultivation, harvest and growth.
Introduction to Rice:
Rice is the principal food crop and the most extensively grown cereal in the tropical and subtropical regions, major portion being grown in China, India, Pakistan, Japan, Southern Asia and the adjacent islands of the Pacific. The area under this crop in India is roughly 38 per cent of the total area under cereals and about 23.5 per cent of the total cropped area. In India, rice has been cultivated since very ancient times. The carbonized grains obtained in India could be dated around 2,300 B.C.
The area under rice crop in India and it production were around 42 million hectares and 70 million tonnes, respectively in 1988-89. It is grown practically in all the states of the country, extending from the delta region of the south to the higher altitudes of about 2,000 m above sea level in the Kashmir valley.
The major rice-producing states are Assam, Bihar, Orissa, West Bengal, UP., MP, Maharashtra, AP, Karnataka, Tamil Nadu and Kerala. Together they account for more than 90 per cent of the total acreage of the crop and 86 per cent of the total production in the country.
Rice (Oryza sativa L.) belongs to the genus Oryza, which includes 23 species (according to some 28 species). Of these, only two, O. sativa and O. glaberrima, are cultivated and the others are wild. In India, five species of Oryza are found. All rice varieties of Asia, Europe and America belong to O. sativa, while many cultivated varieties of West Africa belong to the species, O. glaberrima.
The cultivated species, O. sativa, has probably originated in the south and the southeast tropical Asia, where the greatest diversity of cultivated forms occurs.
The common wild rice of India, O. saliva var. fatua, occurs as a weed in rice fields. This wild rice is believed to be the immediate progenitor of cultivated rice and it is probable that O. sativa has originated from the wild rice by mutation and selection. Since its origin, rice has undergone genetic diversification resulting in the development of thousands of varieties, which are being grown all over the world.
On the basis of geographic adaptation (adaptation to temperature and photoperiodic conditions), the cultivated rice of the world belonging to O. sativa can be broadly divided into three groups, namely, indica, japonica and javanica. Some rank these groups as subspecies of O. sativa.
Of the groups, javanica sub-species (“bulu”) includes a small number of varieties from Indonesia, adapted to low altitudes; japonica includes verities developed in Japan and adapted to the sub-tropical and warm temperate regions (varieties from Japan, Korea and North China belong to this group); and indica includes all varieties not included in the other two groups (varieties from India, southern China, Taiwan, Sri Lanka and other regions).
Not only morphological and physiological differences exist between the two groups, indica and japonica, but a good amount of hybrid sterility is also present. The other group, javanica is in between the two major groups, indica and japonica and is not of great importance in agriculture.
The varieties of indica yield lower than those of japonica and lodge due to heavy manuring, while the latter, which are short statured, are responsive to heavy manuring and give high yields. The japonicas are reported to be non-photosensitive or low photosensitive and they do not lodge easily.
The cultivated rice, O. sativa, has a somatic chromosome number of 24. Of the 18 wild species, eight are tetraploids and the remaining ones are diploids. O. sativa is usually considered to be a diploid species, but there is evidence to indicate that it is a secondary and balanced polyploid.
Rice is, as a rule, a self-pollinated crop, but natural crop pollination has been reported to the extent of 2 to 7% in different areas.
Oryza sativa L. belongs to the family, Gramineae. It is an annual herb. It may sometimes be perennial also. Culms are up to 1.5 m tall; more in the case deep water varieties. Leaves flat, linear and acuminate sheathed at the base; sheaths smooth with ciliate auricles; ligules long, lanceolate, finally splitting.
Inflorescence a lax erect panicle; rachis are more or less robust, angled and channelled. Spikelet’s 3-flowered, awned or not; the terminal floret fertile, the lower 2 sterile; the glumes represented by obscure scales at the apex of the peduncle; fertile lemma strongly laterally compressed, finely granulate, folded and keeled, acute, with a short own, 3-5 nerved; lower empty lemmas oblong-lanceolate, acute or subulate, entire or toothed at the top; palea as long as lemma, 3-nerved, keeled; lodicules 2, entire or 2-lobed.
Stamens 6, is with slender filaments, Ovary superior, 1-celled with one anatropous ovule. Styles 2and Stigmas 2 are laterally exserted, plumose. Fruit a caryopsis, oblong, angular, free or adnate to the lemma and palea, more or less 1 cm long. The outer layer of the kernel, enclosed by the husk or hull or lemma and palea, is the pericarp.
The pericarp may be white or coloured and it consists of epicarp, mesocarp and the cross layer. Attached to the pericarp and on its inner side is the thin testa and below it is the aleurone layer. The bulk of the kernel is made up of the endosperm, which may be glutinous or starchy. A good deal of variation exists in regard to grain size.
Climate Required for Rice Growing:
The climatic factors that influence production of rice to a considerable degree are temperature, day-length and humidity. The crop does best under high temperature, high humidity and prolonged sunlight. Cultivation of rice in the world is spread over a vast area, extending from Australia in the south to Japan and China in the north, i.e., from 39°S latitude to 45°N latitude and 50°N latitude.
In India, the rice area extends from 8°N latitude to 34°N latitude. Rice is grown even in areas below the sea level, as is done in certain parts of Kerala. It also does well at elevations above 1979 m, as in some parts of Jammu and Kashmir. Rice is cultivated as a rain-fed upland crop in the states of West Bengal, Bihar, UP, etc., where the monsoon rain and its distribution are erratic.
Further, in parts of the first two states, rice is also grown in shallow and deep water (4.75 to 6 m). So far as temperature is concerned, the crop requires a range of 21°C to 35°C throughout its life period. Rice is essentially a short-day plant. However, varieties may be sensitive or insensitive to day-length, temperature or to both.
The rice-growing seasons depend on climatic conditions and vary in different parts of India. Under tropical and subtropical conditions, rice can be grown practically throughout the year, while under temperate conditions and at high altitudes, it is grown only in warm part of the year.
The main cropping seasons in India are, autumn (aus), winter (aman) and summer (boro). In the first season, sowing and harvesting area done in May-June and September-October respectively; in the second, in June-July and November- December respectively; and, in the last season, they are done in November-December and April-May respectively.
Yields are generally higher in the rabi season than in the kharif season. With the introduction of short-duration, photo-insensitive varieties double or triple cropping is being done in most rice-growing areas in India, depending on availability of irrigation water.
Soil Required for Rice Growing:
The major soil groups, in which rice is grown, are:
(i) Riverine alluvium,
(ii) Red-yellow,
(iii) Red loamy,
(iv) Hill and sub-montane,
(v) Terai,
(vi) Laterite,
(vii) Coastal alluvium,
(viii) Red sandy,
(ix) Mixed red and black, and
(x) Medium and shallow black.
The most suitable soils are the heavy clays, clayey loams and loams. Such soils can hold water for a long time and thus sustain the crop.
Rice can grow normally without any soil amendment if the soil pH is between 5 and 8.5. The crop can, however, grow even in extreme soil conditions, as in peaty soils of Kerala with pH as low as 3 and also in alkaline soils of Punjab, Haryana and UP with pH as high as 10.
In high and medium lands having irrigation facilities, rice is grown in rotation with jute, wheat, pulses, vegetables, etc. In low-land areas, where stagnant water is present, and in areas, where the rainfall is heavy, rice is grown year after year without rotation with any other crop.
Cultivation of Rice:
The principal systems of rice cultivation in India are ‘dry’, ‘semi-dry’ and ‘wet’. The first two systems of cultivation are confined to areas, which do not have irrigation facilities and hence depend on rains, while the third System is adopted in areas, where the supply of water is assured, either by way of rainfall or by irrigation.
In the dry and the semi-dry systems, the steps are essentially the same. The land is ploughed and harrowed in summer in order to obtain a proper tilth. Farmyard manure is applied to the land uniformly, about 2-3 weeks before sowing. The seed is sown as soon the monsoon starts, either by broadcasting, dibbling behind the plough or by drilling in lines running about 20-25 cm apart.
In the case of semi-dry system, the rain-water is impounded when the age of the crop is 1-1½ months, and after that, it is handled as a wetland crop. In the wet system, the land is irrigated and ploughed thoroughly and puddled with 3-5 cm of standing Water in the field. Puddling of the soil is done primarily to obtain a soft seed-bed. Finally, the land is levelled in order to facilitate a uniform distribution of water and fertilizers.
Under this system, seeds may be sown directly after sprouting them or seedlings may be transplanted. Transplanting in a field has a number of advantages, such as, reduced weed problem, more uniform plant population, increased availability of plant nutrients, quicker establishment of seedlings, etc.
Sowing:
For direct sowing by broadcasting, the seed rate is 80 to 100 kg/ha and for dibbling, it is 60-70 kg/ha. Only well-filled viable seeds should be used for sowing. Treatment of seed with Agrosan at the rate of 100 g per 50 kg of seeds is generally considered useful to prevent the appearance of seed-borne diseases.
In the case of ‘wet’ system of cultivation, the crop is grown by raising seedlings in nurseries and transplanting them in the field. Sometimes, sprouted seeds are broadcast in puddled land. For transplanted crops, seedlings are raised in either dry or wet nursery. The nursery area required for raising seedlings for transplanting one hectare is roughly 1/10th of a hectare and the seed-rate is 40-50 kg/ha.
Nursery Raising:
The common method adopted in India is to raise seedlings in wet nurseries. The other method followed is the dry method. Besides these two, the “dapog” method has been suggested for areas where seedlings for transplanting are required within a fortnight.
(i) Wet Nursery:
The land is ploughed in dry condition and then puddled by ploughing in standing water, three or four times, as in the case of ‘wet’ system of growing the main crop. Farmyard manure, green manure or compost can be applied at the rate of 5- 8 t/ha at the time of first puddling, 3-4 weeks before sowing of seeds. The field is then levelled and raised beds are made.
Sprouted seeds are broadcast uniformly on the mud and a thin film of water is allowed to remain in the bed until germination is complete. If the soils are poor, the seed beds are fertilized with N, P and K (0.5 to 1 kg of N, 0.5 kg each of P2O5 and K2O for 100 m2 area of the nursery). Pests and diseases should be controlled by the use of insecticides and fungicides. Care should also be taken to keep the nursery free of weeds.
(ii) Dry Nursery:
Dry seed beds are raised in areas, where water supply is not assured. The field is ploughed 4 or 5 times to bring it to a fine tilth. Farmyard manure or compost is incorporated into the soil at the rate of 10-15 t/ha, 2-3 weeks before sowing. Raised beds, 15 cm in height, with a 40-50 cm wide drainage channel all around are prepared. Seeds are sown dry either by broadcasting or in lines closely. The nursery beds are watered by sprinkling them periodically. Timely weeding and plant protection measures are also necessary.
(iii) Dapog Nursery:
This nursery, which may be called a portable paddy nursery, was introduced in India from Philippines. In this case, the seedlings are grown on a concrete floor or on a raised bed of soil covered with polythene sheets. This system is adopted especially in areas of assured water supply and when early transplanting is considered necessary. The area required for this type of nursery is small, about 10 sq. meters for one hectare of transplanted land, and the seedlings raised in it get ready for transplantation after a fortnight.
The land preparation, if necessary, is done as in the case of wet-bed method and raised seed-beds are made and packed after the soil is properly levelled. Polythene sheets of the required size are spread tightly on them. Pre-germinated seeds are sown on the top of these sheets, the rate-being 1 kg per square meter of the nursery-bed.
Water is sprinkled on the germinating seeds, which are pressed down gently with hand or a light wooden plank, twice a day, for the first 3-6 days to prevent the roots from being exposed to the air and also to enable them to remain in contact with water retained on the surface.
After six days, the seed beds can be irrigated up to a depth of 1-2 cm of water. The polythene sheets containing seedlings are rolled like a mat and taken to the field, where the seedlings are transplanted. If the polythene sheets are big, they are cut into convenient sizes and then rolled.
As the seedlings are quite small, the water level in the main field has to be properly controlled, because, in case too much water is let in, the seedlings are likely to be damaged. Instead of polythene sheets, banana leaves, empty gunny bags or a 5 cm-thick layer of paddy husk can be used in this method.
Transplantation:
In kharif, the seedlings are ready for transplantation in 20-25 days and, in rabi, in 30-40 days. When seedlings attain optimum age, they are pulled out with care so that no damage is done to the roots. Two to three seedlings are planted per hill at a spacing of 20 × 10 cm or 20 × 15 cm.
Closer planting is recommended in case of late planting and also in areas of low fertility. Transplanting is done in the puddled field, for which land preparation is done thoroughly. The optimum time for transplantation of the main season crop is from 15th July to 15th August.
Weed Control and Management:
While weeding in line-planted or drilled rice can be done with a hand-hoe or rotary weeder, in a broadcast crop, hand-weeding is still the common practice. Herbicides like Butachlor, 2, 4-D and Propanil can be used satisfactorily for controlling weeds in rice fields.
Rice has a high requirement of water as compared to other cereals of similar duration, the range being from 37 to 75 acre inches in different locations in India. After transplantation, water is allowed to stand in the field up to a depth of 1.5- 2.5 cm. When the seedlings are established, about 5 cm of water is maintained in the field till the dough stage of the crop. This is done by frequently irrigating and draining the field. A couple of weeks before the harvest, the water is drained off completely.
Fertilization and Manuring:
The new short-statured varieties in particular respond to high doses of fertilizers and hence their introduction has increased the fertilizer requirement of rice considerably. Nitrogen, phosphorus and potassium are the major nutrients of rice and, among the micronutrients, zinc has assumed importance. Since applied nutrients, particularly nitrogen, are rapidly lost under rice-growing conditions, it is very necessary to improve the efficiency of fertilizer-use. Both organic manures and chemical fertilizers are important for rice cultivation.
Use of Nitrogenous Fertilizers:
Nitrogen is the most important nutrient for the rice crop in almost all soils. Ammonia or ammonium form sources are utilized better by the crop than nitrate sources. The optimum dose of N for the new varieties is 80-100 kg per hectare during kharif and 100-120 kg per hectare during rabi.
In areas, where the soil fertility is low, a part of N should be applied as basal dose, in the form of farmyard manure, composts, oilcakes, leaves of leguminous plants, etc., and incorporated into the soil. Green-manuring with dhaincha (Seshania spp.) is also commonly done in certain areas. Other green-manuring crops used are sunnhemp, guar (Cyamopsis spp.), cowpea, etc.
It has been found that good results are obtained if basal application of nitrogen in the form of urea is followed by top-dressing it at the tillering stage, a week or so before panicle- initiation. The applied nitrogen is better used by the plant and the grain-yield is increased if the placement of the fertilizer is done in between the hills near the root system at the early tillering stage. This is particularly so when the dose of fertilizer is moderate.
Use of Phosphatic Fertilizers:
Phosphorus is absorbed vigorously by the rice plant during its tillering and elongation stages. The requirement of this element in the case of low-land rice is, however, less pronounced than its requirement of nitrogen. Fertilization with phosphorus is difficult in certain types of soil, namely, acid laterite soils, black clay soils and coastal sandy soils, on account of the fixation of large amounts of phosphates in the soil.
The optimum dose of phosphorus for rice varies considerably with the type of soil, conditions of rice cultivation, the source of phosphorus used and also the variety of the crop. For soils, which are deficient in phosphorus, 40 to 60 kg of P2O5 per hectare can be used profitably.
As regards the source of phosphorus, superphosphate is regarded as very suitable for all rice soils except highly acidic ones. The best method of application of phosphatic fertilizers is as a basal dose at the planting time or at the time of final puddling.
Use of Potassic Fertilizer:
Potassium is generally not required by the rice crop in Indian soils, which are known to be fairly rich in this element. Moreover, its requirement for rice is met to a considerable extent by stubble and crop residues, which are incorporated into the soil. Irrigation water also supplies some amount of potassium to the plant.
However, potash fertilization has been found necessary in light-textured and coastal sandy soils if high-intensity cropping is adopted and the recently introduced high-yielding varieties grown. Application of 20 to 50 kg per hectare of K2O is beneficial to the crop, the exact amount depending on various factors like season, soil condition, etc.
Use of Zinc:
Zinc is an essential micronutrient for rice, the deficiency of which is found in soils of high pH. Acid soils may, however, develop deficiency of the element when they are submerged. This happens on account of the possible rise in pH of these soils after they are flooded.
Zinc deficiency in alkaline soils may increase if the organic matter content is high. Further, neutral or calcareous soils become deficient in zinc as a result of continuous submergence. Application of excessive quantities nitrogen and phosphorus also leads to fixation of zinc as a result of enhanced microbial activity.
Rusty brown spots appear and the older leaves get discoloured as a result of deficiency of this clement. Besides, tillering and growth are also affected adversely. Application of 40.50 kg/ha of zinc sulphate to the soil after draining the field or resorting to foliar application of 0.2 per cent zinc sulphate solution arc some of the methods for checking the deficiency.
Use of Blue-Green Algae:
Many species of blue-green algae can fix atmospheric nitrogen. It has been found that the species, Tolypothrix tenuis, from Borneo, is a very good nitrogen fixer and it could fix about 208 kg of nitrogen per hectare per year. Experiments conducted have now proved that the yield of rice can be increased by inoculating the soil with Tolypothrix tenuis.
Harvesting and Threshing:
Harvesting of the crop has to be done in time to prevent losses on account of grain shedding. The water in the field is drained out about 10 days earlier. Early and medium varieties should be harvested 25-30 days after flowering and late varieties after 35-40 days. Paddy should be harvested when the grain has a moisture content of 20-25%. At the time of harvest, the ears are nearly ripe and the colour of the straw is slightly green.
The plants are cut by farmers with sickles, left in the field for a few days to dry and then stacked on the threshing floor. Threshing is done after a week or so by beating the plants against a wooden log or by trampling them by bullocks. Various mechanical threshers are now popular among the farmers. Winnowing is done by hand or by a winnower. The grain is thus separated from the chaff.
The produce obtained after threshing and winnowing is known as rough rice, paddy or grain, which is cleaned and dried in the sun preferably on a concrete floor. Shelling or hulling is done for removing the hull or husk. Milling is done before it is consumed. The highly milled rice is referred to as head rice, brokens, screenings or brewers’ rice on the basis of karnel size.
Yield, Storage and Uses of Rice:
The yield of paddy depends on various factors, like season, cultivation method, condition of soil, manuring, irrigation and variety. It usually ranges from 15 to 80 quintals per hectare.
Storage:
The produce should be properly stored. Generally unhusked paddy is stored in gunny bags. If paddy is stored in moist condition, it may be attacked by fungus. This would cause discolouration of grain, and bad odour and bitter taste would also develop. Controlled mechanical drying is very necessary for keeping the stored paddy in proper condition.
Use:
The grain of rice is chiefly used as food. No other cereal is used by so many people. The rice straw is used as cattle feed and for making straw boards, papers and mats. Rice-bran oil is used for making soaps and cosmetics. Intoxicating beverages are prepared from rice in some parts of India and in several other tropical countries of the world.
Varieties of Rice:
Research work for the improvement of rice was undertaken in India in the beginning of this century and superior varieties were developed and released by the Departments of Agriculture of impartment rice-growing provinces (states). The establishment of the Central Rice Research Institute at Cuttack just before independence gave a boost to rice research in the country and the work on the development of varieties with good yield of grain and other desirable attributes was pursued vigorously.
Later, in the sixties, the tempo of work increased manifold with the implementation of the Coordinated Rice Improvement Project by ICAR and by the introduction of high-yielding dwarf varieties of rice from Taiwan and the Philippines, which have since been used suitably and a large number of high-yielding varieties with certain other superior characteristics evolved and tested all over the country.
So far as West Bengal is concerned, the high-yielding varieties, which have been notified for large-scale cultivation in different agro-climatic regions, and also a few suitable indigenous varieties are indicated below:
Drought-Resistant Varieties:
Varieties of rice tolerant to drought, which are available for growing in different parts of the country are N 22, Bala, Brown Gora, White Gora, Black Gora, IET 1444 (Rasi), Lai Nakanda, CR 143-2-2, Kanchan, Kiran and Bhavani.
Diseases of Rice:
Of the rice diseases, the more important ones are:
(i) Blast caused by Piricularia oryzae, which can be controlled by seed treatment with Agrosan GN or Ceresan before sowing @ 2-2.5 g/kg and by growing tolerant varieties;
(ii) Helminthosporiose (brown spot) caused by Cochliobolus miyabeanus, which can be controlled by adopting the same methods as in No. (i) above;
(iii) Bacterial blight caused by Xanthomonas oryzae, which can be controlled by using seed from disease-free crop and treating the seed by soaking it for 12 hours in a mixed solution of Streptocycline (0.015%) and wettable Ceresan (0.05%), followed by hot-water treatment at 52° – 54°C for 30 minutes and also by growing tolerant varieties;
(iv) Bacterial streak leaf caused by Xanthomonas translucens f. sp. oryzae, which can be controlled by the same methods as in the case of No. (iii) above;
(v) Sheath blight caused by Rhizoctonia solani, which can be controlled by seed treatment with 75% Thiram (@ 0.25%), soil application of 25 kg/ha of Thiram before transplanting and by growing resistant varieties;
(vi) Root rot caused by Rhizoctonia spp., which can be controlled by flooding the nursery-beds with water and by rotation of nursery-beds;
(vii) Foot rot or Bakanae disease caused by Gibberella fujikuroi, which can be controlled by seed-treatment with Ceresan or Agrosan GN (@ 2-2.5 g/kg) or Thiram (0.25%) and by growing resistant varieties;
(viii) Ufra disease caused by Ditylenchus angustus, which can be controlled by burning all infected straw;
(ix) Yellow dwarf caused by Mycoplasma, which can be controlled by spraying insecticides to reduce the population of insect vectors, roguing out diseased plants and by growing resistant varieties;
(x) Leaf yellowing (Tungro) caused by virus, which can be controlled by spraying a systemic insecticide (Thimet) to reduce the insect-vector population, by roguing out diseased plants and also by growing resistant varieties;
(xi) Stem rot caused by Leptosphaeria salvinii, which can be controlled by applying an organo-mercurial fungicide @ 4 kg/ha at the base of plants, by burning straw and stubble and also by growing resistant varieties.
Insect Pests of Rice:
The more important insect pests of rice are:
(i) Stem borer (Tryporyza incertulas), which can be controlled by ploughing the land immediately after harvest and destroying stubbles, giving three fortnightly sprayings with 0.4% Diazinon or Phosphamidon or two applications of Phorate (10%) or Lindane (2%), 2 and 6 weeks after transplantation.
(ii) Gundhibug (Leptocorisa varicornis), which can be controlled by adopting clean cultivation and dusting 10% BHC just before flowering.
(iii) Rice hispa (Dicladispa armigera), which can be controlled by adopting clean cultivation, clipping off leaf tips at the time of transplanting and dusting 5% BHC.
(iv) Swarming caterpillar (Spodoptera mauritia), which can be controlled by flooding the fields or surrounding them with trenches having steep sides, by dusting 10% BHC or spraying 0.03% Dichlorvos or Endosulfan;
(v) Rice grasshoppers (Hieroglyphus banian) which can be controlled by ploughing deep after harvest and by dusting with 5-10% BHC.
(vi) Paddy jassids (Nephotettix apicalis), which can be controlled by spraying 0.04% Phosphamidon or Diazinon or by applying as preventive measure, Phorate (10%), or Lindane (2%), 3 and 6 weeks after transplantation.
(vii) Paddy gall fly – gall midge (Pachydiplosis oryzae), which can be controlled by removing weeds from bunds, by spraying 0.03% Phosphamidon or Dimethoate, 4 times during the vegetative phase of the crop and by growing resistant varieties.
(viii) Paddy mealy bug (Ripersia oryzae), which can be controlled by pulling out and destroying infested plants in the initial stage and by spraying 0.04% Phosphamidon, Diazinon or Monocrotophos.
Some of the rice varieties resistant or tolerant to diseases or insect pests are:
