Rice in India : A Status Paper
METHODS OF CULTIVATION OF RICE
In India Rice is mainly grown in two types of soils i.e., (i) uplands and (ii) low lands. The method of cultivation of rice in a particular region depends largely on factors such as situation of land, type of soils, irrigation facilities, availability of labourers intensity and distribution of rainfalls. The crop of rice is grown with the following methods :-
Dry or Semi-dry upland cultivation
(a) Broadcasting the seed
(b) Sowing the seed behind the plough or drilling.
Wet or lowland cultivation
(a) Transplanting in puddled fields.
(b) Broadcasting sprouted seeds in puddled fields.
Selection of Seeds
The use of quality seeds in cultivation of rice is an important factor to get better crop yield. Therefore, proper care has to be taken in selecting seeds of the best quality. Much of the success in raising the healthy seedlings depends on the quality of seed. Seeds intended for sowing should satisfy the following requirements :-
- The seed should belong to the proper variety, which is proposed to be grown.
- The seed should be clean and free from obvious mixtures of other seeds.
- The seed should be mature, well developed and plump in size.
- The seed should be free from obvious signs of age or bad storage
- The seed should have a high germinating capacity.
Before sowing the seed should be treated with fungicides which protects the seed against soil-born fungi and also give a boost to the seedlings.
Methods of Nursery Raising
There are three major methods of raising nursery - viz.
- The dry nursery where the dry seed is sown in dry soil. This method is practiced in areas where water is not sufficient to grow seedlings in wet nursery
- Wet nursery where sprouted seed is sown on the moist puddled soil. Wet nurseries are preferred under irrigated condition
- And the "dapog" method. This method of raising nursery has been introduced in India from Philippines.
"Dapog" method is commonly prevalent in Philippines. The essential feature of this method is to have a very thick stand of the nursery seedlings without any contact with the soil. Generally, seedlings become ready for transplanting in 12 to 14 days.
The seed rate naturally influences the growth of the seedlings. Thin sowing gives strong and tillered seedlings, whereas thick sowing provides thin and tall seedlings without tillers. Thin sowing in nurseries is always better and it will produce strong and sturdy seedlings, which can withstand adverse climatic conditions better and produce better yields. Therefore, 40 to 60 grams of seed per square metre should be sown in the nursery beds. About 500 square metre area of nursery is sufficient to transplant one hectare area. In case of late sowing of nursery, the nursery area should be increased to 750-1000 square metre.
Before transplanting, field should be puddled properly with bullock or tractor drawn puddlers. Puddling is a very important operation in transplanted rice. Puddling helps to kill the weeds and buries them in puddled soils. It also suppresses the germination of weeds in subsequent growing period of crop. Puddling keeps the soil surface in a more even condition, besides creating beneficial physical, biological and chemical conditions for rice plant growth.
Transplanting should be done with proper age of seedlings. In case of short duration varieties, the seedlings should be uprooted from the nursery beds for transplanting , when it is three to four weeks old. In case of medium and long duration varieties, four to five weeks old seedlings should be transplanted. Always healthy seedlings should be used for transplanting at the four to five leaf stage or when they are about 15-20 cms. high. As far as possible, delayed transplanting should be avoided because it leads to poor tillerings, early flowering of the main tillers and resulting in reduction in yield. In alkaline soils aged seedlings of 45 days old should be transplanted because old seedlings establish better than young seedlings of 25 days age or so.
Under good management and adequate nitrogen levels, the optimum spacing for varieties like IR-8 should be around 20x10 cms both for kharif and rabi crops. With excellent cultural practices, the spacing may be slightly wider, say 20x15 cms but under sub-normal conditions, the spacing should be slightly narrower, say 15x10 cms.
Number of Seedlings per Hill
Transplanting two to three seedlings per hill under normal conditions is enough. The use of more seedlings per hill, besides not being any additional advantage, involves an extra expense on seedlings. In case of transplanting with old seedlings, the number of seedlings per hill can be increased.
Depth of Planting and Directions of Rows
Depth of planting has assumed considerable importance after the introduction of high yielding varieties. The high yielding varieties are characterized with high tillering capacity. The high tillering potential of these varieties is, however, best expressed with shallow planting. The tiller buds formed at the basal node are not suppressed in case of shallow plantings . Therefore, the seedlings should be transplanted at 2 to 3 cm depth. Shallow planting gives better yields. The deeper planting results in an increased height of the plants besides delays and inhibits tillering.
The crop planted with rows running in the north-south direction generally gives better yield particularly in rabi season. The adoption of this practice is worthwhile, since it does not involve any extra expenditure.
Practices in the Direct-Seeded Crops
The success of the direct seeded rice depends entirely on the monsoon rains, besides proper stand of crop. If sowing is done in a properly prepared land, proper stand of crop can be achieved. A field with fine tilth facilitates the seed to come in contact with the soil moisture after drilling and enables the seed to germinate quickly and uniformly. Thus, an ideal preparation of the land will help to achieve a uniform stand, facilitate weeding and fertilizer practices. Therefore, with number of ploughings of the field and timely sowing, the direct seeded crop generally gives better yield.
Different Methods of Seeding
Seeding is done in three different ways - viz. (i) drilling i.e. sowing in the furrow behind a plough, (ii) dibbling and (iii) broadcasting. The light soils which generally come into conditions quickly, any method can be adopted. Seeding with drilling method has got a greater advantage over other methods, because of the uniformity of the stand and the control of the population of the plants per unit area. Heavy soils which do not come in conditions quickly, other methods except broadcasting are not feasible. It has been found that drilling or dibbling always gives considerably better yields than broadcasting system.
Broadcasting Sprouted Seeds in Puddled Land
This method is adopted in an area where agricultural labourers are not easily available for transplanting or some time labourers are very expensive. In this method field is prepared and puddled just like in the case of transplanting. About 100 kg seed is required for one hectare area. In the puddled field sprouted seeds with radical length of one to two millimeter are uniformly broadcast by hand.
Manure and Fertilizer Application
Organic manures are as much as important for rice cultivation as inorganic fertilizers. In case of upland rice cultivation, the use of bulky organic manure is very much desirable in order to maintain the physical condition of the soil and also to increase the water holding capacity of the soil for maximum utilization of rain water. In upland fields 10-15 tonnes of well rotted Farm Yard Manure or compost should be applied in one hectare area preferably 4 to 6 weeks before sowing. Organic manures should be spread evenly on the upper surface of the soil and ploughed in to get it well mixed in the soil.
Application of chemical fertilizers depends basically upon (i) fertility states of the field and (ii) previous crop grown and amount of organic manure applied. Before deciding the fertilizer dose, soil is required to be got tested to know the status of the nitrogen, phosphorus and potassium in the soil. After testing the soil, fertilizer dose should be calculated accordingly.
Soil fertility status varies in different agroclimatic zones to a considerable extent. Therefore, common fertilizer dose can not be recommended for all regions. The Department of Agriculture of various states and State Agriculture University have formulated fertilizer recommendations for rice crop in their states keeping in view the variability in soil fertility and local conditions. The fertilizer dose recommendation by the Agriculture Department in different states are given in Table-4.
Application of fertilizer in transplanted rice field is quite different from upland rice. A series of reactions-physical, chemical and biological take place in transplanted rice fields due to presence of excess water in the field. In the root zone anaerobic environment is formed from aerobic condition due to depletion of oxygen in the soil profile, which is responsible for gaseous loss of nitrogen fertilizer due to de-nitrification process. This anaerobic environment also affects the behavior of phosphorus and micro-nutrients specially iron and manganese.
The soil in the transplanted rice fields after puddling develops two zones in water logged conditions. The upper layer of soils ( 1 to 10 millimetre thick) generally receives Oxygen periodically from fresh supplies of irrigation water and turns in to brown colour called "Oxidised zone" and reacts like an unflooded upland soil. The remaining lower portion of puddled soil without oxygen is called "reduced zone". When ammonical nitrogen fertilizer is applied in such soils, it gets oxidised to nitrate (NO3 ) form in the oxidised zone (upper surface layer of the soil). Afterwards nitrate nitrogen is leached down to the reduced zone and further gets denitrified to gaseous nitrogen. This gaseous nitrogen is lost. If ammonical nitrogen is incorporated in to the reduced zone of the soil, where it is held, the loss can be prevented. Fertilizers containing nitrogen in the nitrate form are more susceptible to loss of nitrogen through leaching and de-nitrification process. Therefore, ammonical form of nitrogen is found more beneficial for rice crop.
Due to variation in soil fertility, rainfall and climatic condition , a common dose of fertilizer can not be recommended for all regions. However, in general a level of 30 to 40 kg of nitrogen per hectare in kharif and 60 to 80 kg of nitrogen per hectare in rabi appears to be the optimum dose for the tall indicas and double that level for the high yielding varieties on soils of average fertility in the southern and eastern regions. In the northern region, where sunshine is available for longer hours, higher dose of nitrogen is beneficial in the kharif season.
The maximum efficiency can be obtained in the direct seeded upland rice by applying 50% nitrogen dose, three weeks after seeding, 30% at 45 days age and the rest at the boot-leaf stage.
In order to obtain better results, full dose of phosphorus, potash and half dose of nitrogen should be applied before last puddling. Remaining half dose of nitrogen should be applied in two equal doses, first at tillering stage and second dose at panicle initiation stage.
The water requirement of rice crop is comparatively higher than any other crop of the similar duration. Assured and timely supply of irrigation water has a considerable influence on the yield of the crop. During the crop growth period, the water requirement is generally high at the initial seedling establishment stage. After the transplanting , water should be allowed to stand in the field at a depth of two to five centimeters till the seedlings are well established. The second, the most important critical stage is tillering to flowering and in this period the crop should not be subjected to soil moisture stress. The water supply should be ensured in required amount during panicle initiation to flowering stage. About five centimeters depth of water should be maintained in the field up to the dough stage of the crop. Before harvesting, water should be drained out from the field to allow quick and uniform maturity of grain.
Harvesting and Threshing
The maximum quantity and better quality paddy and rice depend on the harvesting of the crop at the correct maturity stage. Therefore, it is of the paramount importance to harvest the crop at suitable time. Harvesting of the crop when it is not fully matured might result in loss of yield with poor quality grains. If harvesting is delayed, grain may be lost due to damage by rats, birds, insects, shattering and lodging. Thus, timely harvesting ensures better yield, good quality of grains, consumer acceptance and less breakage when milled. The right stage for harvesting as commonly understood by laymen is when panicles turn into golden yellow and the grains contain about 20 percent moisture. When the moisture in the paddy grains reaches 16-17% in the standing crop in the fields, the crop sustains a heavy loss owing to shattering and damage by birds and rodents.
Extensive studies have been carried out on specifying the optimum time of harvesting. Based on the results of the various studies, in general, three criteria are taken into consideration to specify the right time of harvesting viz. (i) the moisture content of the grains, (ii) the number of days after planting or flowering and (iii) the dry matter of the plant or seed.
The most common and old methods of threshing of paddy is trampling by bullocks or lifting the bundles and striking them on the raised wooden platform. Now pedal threshers are being used. Power driven stationary threshers are also used for quick threshing.