RICE(Oryza sativa)
It is the staple food crop for more than 60 per cent of the world people. In some countries, attractive ready to eat products, which have, long shelf life e.g.popped and puffed rice, instant or rice flakes, canned rice and fermented products are produced. Protein is present in aleuron and endosperm (6–9%) and average is 7.5%. Rice straw is used as cattle feed, used for thatching roof and in cottage industry for preparation of hats, mats, ropes, sound absorbing straw board and used as litter material. Rice husk is used as animal feed, for papermaking and as fuel source. Rice bran is used as cattle and poultry feed and defatted bran, which is rich in protein,can be used in the preparation of biscuits. Rice bran oil is used in soap industry. Refined oil can be used as a cooling medium like cotton seed oil/corn oil. Rice bran wax, a byproduct of rice bran oil is used in industries. Rice bran oil is available in the market in the name of Porna for edible purpose (no cholesterol).
Origin:
De Candolle (1886) and Watt (1862) thought that South India was the place where cultivated rice is originated. Vavilov (1926) suggested that India and Burma should be the origin of cultivated crop.
Species
Rice belongs to genus Oryza and family Poaceae. The genus includes 24 species of which O. sativa and O. glaberrima are cultivated. O. sativa has three sub species viz., Indica, Japanicaand Javanica.
1. Indica:Indigenous to India. It is adapted to subtropical-tropical regions. In India, the varieties are very tall, photosensitive, lodging, poor fertilizer responsive, moderate filling and late matur-ing. The morphological differences between the varieties are very wide and awnless.2. Japanica:It is confined to subtropical temperate regions (Japan, China, and Korea). Varieties are very dwarf, erect, non-lodging, photo insensitive, early maturing, high yielding and fertilizerresponsive. The morphological difference between the varieties is very narrow and awnless. Hence, crosses were made between Indica and Japanica—first cross was ADT 27 during 1964.
3. Javanica:It is a wild form of rice and is cultivated in some parts of Indonesia. Varieties are the tallest, erect, poor filling and awned.
Distribution
It grows from the tropics to subtropical and warm temperate countries up to 40°S and 50°N of the equator. Most of the rice area lies between equator and 40° N and 70° –140° E Longitude. Highest yield was recorded between 30° and 45°N of the equator. The average yield ranges from 2.0–5.7 t/ha in India, China and Egypt lying between 21° and 30° N. The countries near the equator show an average yield of 0.8–1.4 t/ha.
Area, Production and Productivity
In terms of area and production, rice is second to wheat. Maximum area under rice is in Asia (90%). Among the rice growing countries, India has the largest area (42.5 m.ha) followed by China, Bangla-desh and Thailand. The area, production, productivity of rice for the world (continent wise) and some of the important countries is given in Tables 1 and 2.
Climate and Soil
Rice can be grown in different locations under a variety of climate. The Indica varieties are widely grown in tropical regions. Japonicas, which are adapted to cooler areas, are largely grown in temperate countries. Both Indica and Japanica rice varieties are grown in subtropical regions. However, the crosses between Indica and Japanica are grown through out the world. Rice needs hot and humid climate. It is best suited to regions, which have high humidity, prolonged sunshine and an assured supply of water. Temperature, solar radiation and rainfall influence rice yield by directly affecting the physiological processes involved in grain production and indirectly through diseases and pests.
(a) Temperature: Extreme temperatures are destructive to plant growth and hence depended on the environment under which the life cycle of the rice plant can be completed. The critical low and high temperatures for rice are normally below 20°C and above 30°C respectively, which vary from one growth stage to another. Temperature affects the grain yield by affecting tillering, spikelet formation and ripening and it influences the growth rate just after germination and increases almost linearly with increasing temperature within a range of 22–31°C. At later stages, it slightly affects tillering rate and the relative growth rate. During reproductive stage, the spikelet number per plant increases as the temperature drops. The critical temperatures for different growth stages of rice are given in Table 3.
(b) Solar radiation: The solar radiation requirements of rice crop differ from one growth stage to another. Shading during vegetative stage slightly affects yield and yield components. Shading during reproductive stage has a pronounced effect on spikelet number. During ripening, it reduces grain yield considerably because of decrease in the percentage of filled spikelets. Solar radiation at the reproduc-tive stage has the greatest effect on grain yield. The minimum requirement of solar radiation is 300 cal/cm 2/day.
(c) Day length: Rice is a short day plant. Long day prevents or delays flowering. E.g.,GEB 24 is a photosensitive and season bound variety. However the latest varieties released are photo insensitive.
(d)Rainfall: Under rainfed rice culture, rainfall is the most limiting factor in rice cultivation. When irrigation is provided, the growth and yield is determined by temperature and solar radiation. Water stress at any growth stage may reduce the yield. The rice plant is most sensitive to water deficit from the reduction division stage to heading.
(e) Wind: Moderate wind is beneficial for crop growth. High wind at maturity may cause lodging of the crop.
(f)Soils: Rice is a semi aquatic plant and grows best under low land condition. In India, it grows in all most all type of soils; alluvial, red, lateritic, laterite, black, saline and alkali, peaty and marshy soils, and in acid soils. But the soil having good retention capacity with good amount of clay and organic matter is ideal for rice cultivation. Clay and clay loam soils are most suited. It tolerates a wide range of soil reaction from 4.5–8.0. It grows well in soils having pH range of 5.5–6.5. It can be grown on alkali soil after treating them with gypsum or pyrites.
Transplanted rice
Wet nursery: The seed rate of 60 kg/ha is recommended for short duration, 40 kg/ha for medium duration and 30 kg/ha for long duration varieties.
A. Pre-treatment of seeds (before sowing)
(a) Dry seed treatment: Mix any one the fungicide at 2 g/kg of seed (Thiram, Captan, Carboxin or Carbendazim). Treat the seeds at least 24 hrs prior to soaking for sprouting. The seeds can be stored for 30 days without any loss in viability.
B. Treatment of seeds at the time of soaking the seeds for sprouting
(a) Wet seed treatment: Treat the seeds in Carbendazim or Pyroquilon or Tricyclozole solution at 2g/lit of water for 1 kg of seed. Soak the seeds in the solution for 2 hrs. Drain the solution, sprout the seeds and sow in the nursery bed. It gives protection to the seedlings up to 40 days from seedlings disease such as blast and it is better than dry seed treatment.
(b) Seed treatment with Azospirillum: Three packets (600 g/ha) of Azospirillum culture are to the mixed with sufficient water wherein seeds are soaked over night before sowing in the nursery bed. The bacterial suspension after decanting may be poured over the nursery area itself.
(c) Seed treatment with Pseudomonas fluorescence: Three packets (600 g/ha) of Pseudomonas culture should be added in water wherein seeds are soaked over night before sowing in the nursery bed. It can be mixed with Azospirillum culture, as it is not inhibitory to Azospirillum.
C. Soaking and sprouting the seeds
The seeds are soaked for 10 hrs. Drain the excess water. The seeds should not be soaked in running water, which removes the minerals and nutrients. Keep the soaked seeds in gunny bag in dark room and cover with extra gunnies for 24 hrs for sprouting. The seeds should not be covered with thick material, which develops heat and reduces the aeration.
D. Preparation of nursery for sowing
About 20 cents (800 m2) for planting one ha is required. Raise the nursery near the water source. Apply 1 t of FYM or compost to 20 cents of nursery and spread the manure uniformly. Before ploughing, allow water to a depth of 2.5 cm. Before last puddling, apply 40 kg of DAP @ 2 kg/cent. Basal application of DAP is recommended when the seedlings are to be pulled out in 20–25 DAS. If the seedlings are to be pulled out after 25 days, application of DAP is to be done 10 days prior to pulling out. In clayey soils, where root snapping is a problem, DAP has to be applied at 1 kg/cent 10 DAS.
Mark out plots, 2.5 m broad with channels, 30 cm wide in between. Collect the mud from the channel and spread on the seedbed and level the surface of seedbed so that water drains into the channel. Having a thin film of water in the nursery, sow the sprouted seeds uniformly on the seedbed.
E. Water management
For water management in nursery, first drain the water 18–24 hrs after sowing and allow enough water to saturate the soil from 3–5th day. From 5th day onwards, increase the quantity of water to a depth of 1.5 cm depending on the height of seedlings. Afterwards, maintain 2.5 cm depth of water.
F. Weed management
Apply any one of the pre-emergence herbicide like Butachlor or Thiobencarb at 2.0 lit/ha or Pendimethalin at 2.5 lit/ha or Anilophos at 1.25 lit/ha on 8 DAS to control weeds in the nursery. Keep thin film of water at the time of herbicide application and should not drain the water after application.
G. Top dressing with fertilizers
If the seedlings show the symptoms of ‘N’ deficiency and if the growth is not satisfactory, apply urea at 500 g/cent of nursery, 7–10 days prior to pulling. If DAP is applied 10 days prior to pulling, urea application is not necessary.
H. Optimum age of seedlings for transplanting
Short duration varieties : 18–22 days, Medium duration varieties : 25–30 days, Long duration varieties : 35–40 days
I. Main field preparation for transplanted rice
Wet rice requires a well puddled soil. Ploughing under submerged soil condition is called puddling. The land is ploughed repeatedly 3 or 4 times with aninterval of about 4 days between each puddling by country plough or mould board plough or tractor drawn cage wheel or by using power tiller with a standing water of 3–5 cm. Optimum depth of puddling is 10 cm for clay and clay loam soils.
J. Application of organic manures
Apply 12.5 t of FYM or compost/ha and spread the manure uniformly on the dry soil before applying the water. If FYM or compost is not available, apply green manure/green leaf manure at 6.25 t/ha. Compute the green matter using the formula. Yield/m2 in kg × 10,000.
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