CLIMATE AND VARIETIES

Climate

Rice can be grown in both tropical and sub-tropical zones. The crop requires a high temperature, high humidity and optimum moisture during its growth. The average temperature ranges between 21–35 oC. More uniform and warm conditions enable more than one crop to be taken per year. There are both photo-sensitive and photo-insensitive rice varieties, the latter having a shorter maturation period.

Cropping system

Crop rotation is an agronomic practice followed by farmers to make use of nutrients present in the soil in the best possible way. When the same crop is planted every season the soil becomes deficient in a particular nutrient that is utilized largely by that plant. This situation can be prevented by cultivating crops that have different nutrient requirements. When leguminous plants are cultivated, they trap the atmospheric nitrogen and convert it into a form that can be easily utilized by the plants. When the root nodules and leaves of these plants get into the soil, they increase its nitrogen content and help to retain the soil fertility.

In various districts of Tamil Nadu such as south Arcot, north Arcot and Chengalpattu, banana, sugarcane and betel are cultivated as alternative crops for paddy. Cultivating Sesbania as an intermediate crop between two paddy crops gives good results. The following sequence can be maintained.

Rice-based cropping system

Soil

Top soil should be ideally 18–23 cm deep. While cultivating paddy, it is always good to study the type, nature and the nutrient content of the soil before adding nutrients. This can be done by having soil samples tested in a soil-testing laboratory. Manure can be applied based on the nitrogen, potassium and phosphorus content of the soil. In paddy cultivation, the yield will be high when the pH of the soil is between 5 and 6.5. The yield will be poor if the pH of the soil is below 5 or above 9. Alluvial soil, sandy clay and clayey soils are suitable for paddy cultivation.

Varieties

Systematic varietal improvement of rice began at the rice research station, Dhaka (now in Bangladesh) in 1811 with pure line selections (Singh, 2005). The Central Rice Research Institute (CRRI) at Cuttack was established in 1945. This was the centre for the indica-japonica hybridization programme. Enhancing and stabilizing the grain yield potential with suitable plant types in different ecological conditions was the major objective of the rice improvement programme. Grain yield, grain length, cooking and eating quality are taken into consideration for developing ideal varieties. A good number of varieties combining earliness, resistance to biotic and abiotic stresses and grain quality have been developed. Besides these, a number of local varieties suitable for various situations are still preferred, particularly by organic growers. In

Tamil Nadu the following varieties are being cultivated:

• Varieties resistant to drought : Kattu Samba, Sornavari, Puzhudikar, Puzhudisamba, Mattakkar, Vadansamba, Kullakkar, Gil Gil Samba, GEB – 24, Kuzhiyadichan. Varieties resistant to water logging Neelansamba, Kudiraival Samba, Kaliyan Samba, Samba Mosanam, Perungar, Koomvazhai, Kudaivazhai.
  
• Varieties resistant to both drought and water logging : Kappakkar, Vaigunda, Pichavari, Kurangusamba.
  
• Varieties suitable for saline soils : Karuppu nel, Samba, Kuzhiyadichan.
  
• Varieties resistant to pest and disease attack : Kappa Samba, Vadan Samba, Kudirai Vali, Kaliyan Samba, Kurangu, Samba, Kichali Samba, Muttakkar, Kullakkar, Sigappu Kuruvikkar, Thooyamalle, Sembalai, Kallimadyan, Pitchavari, Sadakar.
  
• Variety resistant to brown plant hopper and ear head bug : Neelansamba.
• Variety resistant to brown plant hopper and rice caseworm : Sigappu Kuruvikkar.
  
• Variety resistant to weeds : Vaigunda.

SEED

Selection of seed : Seed selection plays an important role in paddy cultivation. The seeds selected for cultivation should be of uniform size, age and free of contaminants. They should also have good germination capacity.

Separation of quality seed : To separate good seed from bad, soak them in water: the unviable seeds will float on the surface of water. These seeds can be easily emoved and the seeds that sink can be used for cultivation. By this method, damaged seeds are easily removed. Another method is used when there is an excess of chaffy grain in the seed stock. Take some water in a vessel and drop an egg in it. Keep adding salt slowly till the egg reaches the surface. When the seeds are dropped into the water, the good quality seeds will sink. Remove the unviable seeds that float on the surface of the water. Wash the selected seeds in good water 2–3 times to remove the salt deposits. If this is not done, the germination capacity of the seeds will be affected.

Seed rate : The seed rate varies according to the variety to be cultivated. The seed rate required for one hectare of land under irrigated condition is given below:

Germination test : The germination test is considered the most important quality test for evaluating the planting value of a seed lot. The test is designed to measure the ability of seeds to produce normal seedlings and plants later on. The various ways of performing a germination test are listed below:

• Tie a handful of seeds in a white cloth, soak it in water for 12 hours and keep in a dark place for 24 hours. Check the germination percentage the next day.
  
• Tie paddy straw together to make it into a mat. Keep the seeds in the centre of the mat and then roll and tie it. Dip it in water for a minute and transfer the seeds to straw. After 24 hours, count the seeds that have germinated.
• Take a wet gunny bag, fold it, put the seeds in between the two layers and keep the bag in the dark for a day. Check the germination the next day.

Treatment

Seed treatment helps to improve germination potential, vigour, and resistance to pests and disease. The different methods of rice seed treatment are:

• Soaking the seeds in water : Tie the seeds in a small gunny bag or cloth bag and soak it in water for 12 hours. Later, remove the bag from the water and cover it with a moist gunny bag. The following day, soak the seeds in water for eight hours again. Later, remove the seeds from the water and sow them in the nursery. This method helps to improve the germination capacity of the seeds.
  
• Using cow dung solution : Treating paddy seeds in a cow dung solution enhances their germination. Take 1⁄2 kg of fresh cow dung and two litres of cow urine and dilute them with five litres of water. Soak 10–15 kg seeds first in water for 10–12 hours and then in the cow dung solution for 5–6 hours. Dry the seeds in the shade before sowing them in the nursery.
  
• Using goat dung solution : Treating 30-day old seeds for one day in a goat dung solution increases their germination. Using cow's urine solution Dilute 500 ml of cow's urine in 2.5 litres of water. Tie the seeds in small bags and soak them in the urine solution for half an hour. Dry the seeds in the shade before sowing them.
  
• Using sweet flag extract : Dissolve 1.25 kg of sweet flag rhizome powder in six litres of water. Tie the seeds in small bags and soak them in the extract for half an hour. Dry the seeds in the shade before sowing. (This is the quantity required for treating seeds to be sown in one hectare.) Using Salvadora persica Spread the leaves of Salvadora persica at the bottom of a closely- knit bamboo basket, then fill it with seed and pour about 10 to 12 litres of water over the basket. Cover the basket with the Salvadora leaves and place a weight over it. Leave the seeds undisturbed for 24 hours. The seeds are then ready to be used for sowing in the nursery. This procedure helps in early and vigorous germination. Treatment of rice seed with amrut pani/panchagavya/cow pat pit manure/jeevamrut is also effective. The efficiency needs to be evaluated.
  
• Using biofertilisers : Biofertilisers like azospirillum/azotobacter/pseudomonas (@ 1.25 kg/ha) are first mixed in one litre of cooled rice gruel. Spread the sprouted seeds on a clean floor, add the biofertiliser slurry and mix well. The mixing of seed and biofertiliser slurry can be done in a pot as well. Dry the seeds in the shade for 30 minutes before sowing. Drying the seeds for half an hour in the bright sun before sowing improves germination and seedling vigour.

CULTIVATION

Preparation of the nursery bed

Around 800 m2 nursery area is required for raising seedlings needed for one hectare of land. After ploughing the nursery bed (four times), spread neem leaves on the soil. The leaves should be allowed to decay in water for 6–7 days. When the leaves decay completely, the land should be ploughed again four times and levelled. In case neem leaves are not available, 8–10 kg of neem cake and 10–15 kg of vermicompost should be added to the soil during the last ploughing. Later, the soil should be leveled and the seeds sown. Farm waste and trash can be burnt on nursery beds. The heat generated by burning sterilizes the soil and nutrients like potash also get added. Leaves of Adhatoda vasica can be incorporated into the soil while preparing the nursery. This increases soil fertility; acts as an insecticide and renders the uprooting of the seedlings easier.

Note: One may encounter many weeds if farmyard manure is added to the nursery. Hence, it is advisable to avoid it.

Managing problem insects and disease in the nursery

Pests such as the green leaf hopper, green horned caterpillar and diseases such as brown leaf spot and blast generally attack seedlings in a nursery. Hence, the crop is damaged at its very early stages. These attacks can be prevented by spraying two doses of 10% cow's urine extract at seven days' interval at the appearance of the first symptom. This should be immediately followed by pest management techniques. Before plucking the seedlings, the nursery should be irrigated and 15–20 kg of gypsum should be added to prevent damage to the rootlets.

Application of biofertilisers

Azospirillum (@ 2.5 kg/ha) is mixed with 25 kg of farmyard manure and applied in the nursery 30 minutes before plucking. The seedlings are kept submerged in the nursery for 30 minutes and then transplanted.

Main field preparation

The main field should be irrigated and ploughed several times. The bunds should be trimmed and plastered to prevent water leakage. Rat holes found in the field should be sealed. Groundnut or neem cake (@15 quintals/ha) should be applied as basal manure during the final ploughing and the land should be levelled before sowing. At the time of the final ploughing, dried cow-dung and ash mixture can be spread uniformly across the field. This facilitates aeration and activates the microbes in the soil.

Seedling treatment

The paddy seedlings can be treated with ash and neem seed mixture before transplanting. For this, the seedling bundles are kept in small plots of standing water mixed with ash and pulverized neem seeds from 30 minutes to an hour. One kilo of ash and 500 gm of neem seed are sufficient for treating 50 bundles of seedlings.
The treated seedlings produce a crop free from pests and disease. Soak groundnut cake and neem cake in water overnight and filter. Treat the seedlings in this solution before transplantation. The treated seedlings are less vulnerable to pest attack. The paddy seedlings can also be dipped in a solution of amrut pani/ panchagavya/jeevamrut.

Transplantation

The paddy seedlings are transplanted @ 2–3 saplings per hill at a depth of 3 cm. The spacing between the seedlings will vary according to the variety cultivated. Before transplanting, clip off the tips of the seedlings. This facilitates uniform growth and helps to remove egg masses and insect pests present on the leaf-tips.

Note: With old seedlings, varieties with low tillering capacity and soil with very high pH, lesser spacing should be given while transplanting and larger number of seedlings should be used (5–7 seedlings per hill).

Spacing

Weeds

Weeds compete with rice and take away a heavy toll of energy, water and plant nutrients. Generally, they are found more in upland rice than in low land or irrigated rice. Weeding should be done manually and the picked weeds should be trampled into the field for in situ conservation of nutrients and for organic matter as mulch. The first weeding should be done at about 15–20 days after transplantation. About 50 kg neem cake should be applied to the field. Subsequent weedings should be done as and when weeds appear and become problematic. Weeds can be kept under check by flooding the field to a height of 5–8 cm during the early vegetative stages. The most commonly found weeds in transplanted rice are Echinochloa colonum, Echinochloa crusgalli, Cyperus iria, Eclipta alba, Celosia argentia, Dactyloctameum, Setaria glauca, Monocharia spp., Cyperus difformis, Scirpus spp., Fimbristylis litoralis, Marsilea quadrifolia, etc.

Use of calotropis (Calotropis gigantea) as green manure checks the growth of the weed Marsilea quadrifolia. The fibrous pericarp of coconut applied @ 25 baskets/ha also controls this weed to some extent. It releases a tannin-like substance that inhibits the growth of the weed.

While preparing the land, apply leaves and small twigs of Strychnos nux-vomica (poison nut) and incorporate them into the soil. This helps to suppress the weeds.

Updated on : Dec 2014