Transplanting. The seedlings are ready for transplanting in kharif within 20 to 25 days (4-5-leaf stage), whereas in rabi, it may take 30 to 40 days. Two to three seedlings are planted at 20X10 cm or 20X15 cm spacing in levelled fields. In regions of low fertility, and for late planting, closer planting is advocated.
INTERCULTURE AND WEED CONTROL. In line-planted or drilled rice, weeding can be done with a hand-hoe or with rotary weeders. In a broadcast-sown crop, weeds pose a major problem and hand-weeding is still practiced. The best time to weed the crop is three weeks after sowing or planting. Herbicides, such as Butachlor, 2,4-D and Propanil, give a satisfactory weed control in rice and can be used as a tool for controlling weeds, when used at the recommended doses and at the right time. Irrespective of the method of weeding, it is ideal to maintain a weed-free condition up to 40-45 days after sowing.
Water management. the water requirement of rice is higher than that of other cereal crops of similar duration. Figures ranging from 37 to 75 acre-inches of water have been reported from various locations in India, as the water requirement of rice, and this variation is primarily due to different soil and environmental conditions obtaining in different parts of the country.
Losses due to percolation are more in submerged rice lands. In lighter soils, such losses amount to about 60 per cent of the total water requirement. Soil compaction and puddling help to reduce percolation losses.
Losses due to transpiration account for about 40 per cent. Losses due to evaporation depend upon the climatic factors and range from 20 to 40 per cent. Considerable saving (30-40 per cent) in water is possible when shallow submergences (2-5 cm) is maintained from tillering to flowering and near saturation during other phases of growth.
Fertilizer management for rice. The new short-statured varieties have a high fertilizer response and give high yields of grain. The major nutrients required by rice are nitrogen, phosphorus and potassium. Among the micro-nutrients, zinc is becoming important. About a third of the total fertilizer, now available in India, is used for the rice crop alone. However, the rice-growing conditions are equally conducive to rapid losses of applied nutrients. This is particularly true of nitrogen, and this element is usually deficient in most of the rice areas. Rice being a poor utilizer of applied nutrients, there is need to improve the fertilizer-use efficiency.
EFFICIENT USE OF NITROGEN FOR RICE. Among all the nutrient elements, nitrogen is most important for the rice crop in almost all the soils, particularly when nitrogen-responsive varieties are grown. The economic optimum dose of N for the new varieties is 80-100 kg/ha during kharif and 100-120 kg/ha during rabi at the existing price levels.
The added nitrogen is lost from the soil system through mineralization-nitrification-denitrification reactions. This being the case, it is the time and the method of nitrogen application based on the crop-growing conditions and the physiological growth stages of the crop that are more important.
The basal application of a large quantity of N at planting can lead to serious nitrogen losses, unless the applied nitrogen is properly incorporated into the reduced zone of the surface soil. An excessive basal application of N can also lead to extra vegetative growth, the mutual shading of the lower leaves in tall leafy varieties and a consequent reduction in carbohydrates and protein metabolism in the plants. An adequate supply of N in the early stages of growth is, however, essential for growth, tillering and maintenance of root activity and dry-matter production in the case of rice. In soils which are fertile, the basal dose of N may not be required, but in areas where the soil fertility is low and the average yields are less than 3 tonnes per hectare, a part of the N (about one-third) needs to be applied as a basal dose and incorporated into the soil.
The early application of moderate levels of N at planting and tillering are effective in increasing the formation of panicles whereas late applications just before the initiation of panicle increase the number and the size of the spikelets. Increasing the nitrogen content of the leaves to a level, while on optimum leaf area, is essential for securing better nitrogen management and increased grain yield. Nitrogen can be applied either as ammonium sulphate or as urea. The loss of nitrogen from urea, the priciple source of nitrogen, now being manufactured in the country, can go up to 60 to 80 per cent.
The incorporation of the basal applied N as urea into the soil followed by top-dressing it at tillering and about a week before the initiation of panicles is effective over a wide range of situations. The placement of nitrogen in between the hills nearer to the root-system in the reduced soil zone at the early tillering stage increases the N use efficiency as well as the grain yield, particularly at moderate levels of fertilizer application. The application of nitrogen as pre-incubated urea (urea incubated with the soil in 1 : 6 ratio for two days) or as urea incubated with neem-cake has also given better response to the added nitrogen. The application of urea as a slow-release fertilizerhave been found effective. The future use of controlled-release or slow-release fertilizer will, however, depend on the economic feasibility. The future development in fertilizeruse would consist in a judicious combination of organic and inorganic components as well as in biological N-fixation in an integrated nutrient-supply system.
PHOSPHATIC FERTILIZER FOR RICE. Rice also requires phosphorus for its normal growth and yield. However, the phosphorus requirement of the lowland rice is not as pronounced as its nitrogen requirement. In the acid laterites, black clay soils and in coastal sandy soils, fertilization with phosphorus is a problem because of the soil fixation of large amounts of phosphates. The availability of P is increased under flooded conditions owing to the reduction of ferric phosphates to soluble ferrous phosphates on the one hand and the hydrolysis of iron and aluminium phosphates on the other.
The optimum rate of phosphorus for rice varies widely with the soil type, conditions of rice-culture, the source of P used and the variety. Forty to 60 kg of P2O5 per hectare can be used with advantage in soils which are deficient in phosphorus.
Superphosphate is a very efficient source of phosphorus for rice on all soils, except on those which are highly acidic. Phosphatic fertilizers are best applied as a basal dose before planting. Subsequent applications of P, either as a straight fertilizer or as complexes, if done to a certain extent. In acidic soils, rock phosphate can also be used. The application of rock phosphate, at least 15 days before planting, is essential for better utilization.
RESPONSE OF RICE TO POTASSIUM. Rice soils in India are fairly rich in potassium and its requirement by rice to a great extent is met by the incorporation into the soil of stubble and crop residues which contain a lot of potassium absorbed by the plant and also from the irrigation water. However, with the high intensity cropping and the cultivation of high-yielding varieties, potash fertilization can become necessary in light textured and coastal sandy soils.
ZINC AS AN ESSENTIAL MICRONUTRIENT FOR RICE. nbsp Zinc deficiency is commonly associated with soils of high pH above neutrality. It is believed that one-unit increase in pH makes zinc one hundred times less soluble. However, submerged acid soils may, at times, develop Zn deficiency because of the possible rise in pH of these soils after flooding. In alkaline soils, a high content of the organicmatter of the soil tends to aggravate Zn deficiency. The continuous submergence of neutral or calcareous soils leads to zinc deficiency, as the concentration of zinc in the soil solution gets depleted owing to continuous submergence. An excessive use of N and P fertilizers also promotes microbial fixation of zinc.
The appearance of rusty-brown spots and the discolouration of the older leaves, starting from 2-3 weeks after transplanting, are the common symptoms of zinc deficiency. Tillering and growth are also adversely affected by the deficiency of this element.
Draining the field and applying 40-50 kg/ha of zinc sulphate to the soil or making a foliar application of zinc sulphate solution (0.2 per cent) or dipping the roots into a suspension of zinc oxide before planting are the recommended practices to check zinc deficiency.
HARVESTING. Timely harvesting prevents losses in yield because of the shedding of grians. The later stage of grain-ripening is a dehydration process and maturity is hastened when water is withdrawn from the field at the hardening stage of the grains. The timely draining away of water makes the field hard to facilitate mechanical harvesting wherever this system is practiced.
The harvesting of early and medium varieties, 25-30 days after flowering and 35-40 days in the case of late varieties is desirable. Fileld paddy should be harvested when the moisture content of the grain is about 20-25 per cent. This moisture content is to be reduced to 13 to 14 per cent before milling. The direct drying under the sun leads to an increased breakage of the grains during milling. Gradual drying in the shade is essential for better recovery in the mills.
The produce after harvesting is known as rough rice, paddy or grain. The rough rice is milled before it is consumed. The husk or hull, the highly milled rice is white, translucent or opaque and is classified as head rice, brokens, screenings or brewers' rice, according to the size of the kernels.
STORAGE. The proper storage of the produce is necessary. If moist paddy is stored, fungal attack will set in and this would lead to grain discolouration. Bad odour and bitter taste would also develop. For avoiding such defects, the controlled mechanical drying of paddy is a necessity. In advanced countries, mechanical devices and large-scale storage units are available and these facilities can be availed of on custom-service basis. Such a system can be adopted in this country. Alternatively, economical and effective storage structures, now available, can be established at block or district levels.
