DRY AND SEMI-DRY SYSTEMS. Basically, the steps involved are essentially the same under both these systems of rice-culture. The fields are ploughed and harrowed in summer for achieving the required-tilth. Farmyard manure is uniformly distributed 2-3 weeks before sowing. The seed is sown directly with the onset of the monsoon showers, either by broadcasting, dibbling behind the country plough or by drilling in lines. Line-sowing is preferable, as it ensures an adequate stand establishment and facilitates easy weeding and interculture. The reduced seed-rate requirement is another advantage. The row spacing may be suitably adjusted from 20 to 25 cm.
Under the semi-dry system, the rain-water is impounded when the crop is about 1-1/2 - 2 months old and thereafter it is converted into a wetland crop. By that time, major operations, such as weeding, interculturing and fertilizer applications might have been completed. 'Beushening' still prevalent in Orissa and Madhya Pradesh under this system helps to control weeds and adjust population. The latest thinking is to promote line-sowing, using a higher seed-rate so as to have a uniformly higher population density for effective competition from weeds and to use effective methods of inter culture to solve the weed problem.
WET SYSTEM. Under this system, the land is ploughed thoroughly and puddled with 3-5 cm of standing water in the field. The optimum depth of puddling is found to be around 10 cm in the clay and clay-loam types of soils. The primary objective is to obtain a soft seedbed for the seedlings to establish themselves faster, to minimize the leaching losses of nutrients and thereby increase the availability of plant nutrients by achieving reduced soil conditions which facilitates a better availability of nutrient elements, to incorporate the weeds and stubble into the soil and to minimize the weed problem. Puddling can be done with ploughs, tillers or tractors, depending upon their availability and soil conditions. The land is levelled after puddling to facilitate a uniform distribution of water and fertilizer.
Seeds may be sown after sprouting them or the seedlings be transplanted under this system. The weed problem is serious under direct-seeded conditions and is difficult to control completely in a broadcast crop. Water management also poses a major problem in unlevelled lands and, therefore, transplanting has been generally practiced. Transplanting in a puddled field has the following advantages :
1. A good levelling of the land is ensured.
2. The weeds are buried at the time of puddling and the weed problem is reduced.
3. The population of plants becomes more uniform.
4. The availability of most of the plant nutrients, such as phosphorus, iron and potassium, is increased and nitrogen is conserved better.
5. The seedlings transplanted in a soft puddle are able to establish themselves faster and start early tillering and growth.
6. Nurseries occupy only 10 per cent of the main field area and the cost of maintaining them (irrigation and plant protection) is reduced considerably as compared with a crop sown broadcast.
7. Plant-protection measures can be effectively used in the nursery.
8. Community nurseries facilitate timely transplanting.
9. The treatment of seedlings for nutrient deficiencies and for protection against pests and diseases is facilitated before transplanting.
SEED AND SOWING. The seed-rate for direct sowing by broadcasting is 80 to 100 kg/ha and by dibbling it is 60-70 kg/ha. Only well-filled viable seeds should be used for sowing. Lighter seeds that float on a solution of common salt (1.06 specific gravity) should be rejected. The choice of a suitable variety based on topo-sequence, soil type and duration is a prerequisite for obtaining high yield. Seed treatment with Agrosan at the rate of 100 g per 50 kg of seeds is generally recommended to prevent seed-borne diseases. The untreated seeds of high-yielding varieties should be soaked for 12 hours in a solution of wettable Ceresan (0.1 per cent, i.e. 1 gm in one litre of water). The seeds should then be thoroughly dried in shade and used for sowing.
The nursery area required to provide seedlings for transplanting one hectare is roughly 1/10 of a hectare and the seed-rate is 40-50 kg/ha. To ensure rapid and uniform germination, selected seeds should be soaked for 24 hours in clean water, which should be drained away thereafter and the seeds be incubated in a warm, moist place for 36-48 hours to let them sprout for sowing in the nursery.
NURSERY-RAISING. The general practice in India is to go in for wet nurseries. Another system of nusery-raising, known as the "dapog" method, had been recently suggested for areas where the seedlings are to be obtained within a fortnight for immediate transplanting.
Wet nursery. The site selected should be near an assured source of irrigation. The land ploughed twice in the dry conditions and puddled subsequently by ploughing it in standing water (2-3 cm deep) three or four times, preferably at intervals of 5-6 days. Farmyard manure, green manure or compost can be applied uniformly @ 5-8 t/ha at the time of the first puddling, 3-4 weeks before sowing the nursery. The field is levelled perfectly after the final puddling and made into raised beds, 1 - 1-1/2 metres in width and of convenient length, leaving 30 cm of channel space in between the beds. Sprouted seeds are broadcast evenly on the soft mud, and only a thin film of water is maintained. The beds are maintained at the saturation level by sprinkling water periodically to maintain only a very thin of it till such time that the germination is complete and the coleoptile turns green. The level of water is raised gradually and is maintained at a depth of 2-3 cm.
in soils poor in natural fertility, it is advisable to fertilize the seedbeds with 0.5 to 1 kg of N, 0.5 kg of P2O5 and 0.5 kg of K2O for every 100 m2 area of the nursery before the final levelling of the nursery-beds. In regions of low temperature, during rabi it is desirable to supply a slightly higher dose of phosphorus to promote root development and to establish a good stand in the nursery.
Adequate care should be taken to ward off pests and diseases in the nursery itself by spraying it with insecticides and fungicides periodically. The nursery should also be kept free from weeds; otherwise, they are also carried to the main field at the time of transplanting. When the seedlings are at the 4-5 leaf stage, the nursery is adequately irrigated and the seedlings are removed without causing, as far as possible, any damage to their roots. Young, healthy and vigorous seedlings establish themselves faster and grow better and the major objective of nursery-management should be aimed at obtaining such seedlings.
Dry nursery. In regions of non-assured water-supply, where wet-bed nurseries cannot be raised, dry nursery-raising is practiced. The field is brought to a very fine tilth by ploughing it four or five times at 4-5-day intervals. Ten to fifteen tonnes per hectare of farmyard manure or compost is spread uniformly and incorporated into the soil 2-3 weeks before sowing. Raised beds 1 - 1-1/2 metres in width, 15 cm in height and of convenient length, are prepared, keeping a 40-50-cm wide channel all around to facilitate drainage, as and when required. The seeds are sown dry, either broadcast or in lines closely, and are covered with a thin layer of soil or compost. The nursery-beds are irrigated by sprinkling water on them periodically once in 2-3 days, depending upon the soil and environmental conditions. Light soils may require frequent irrigation. Timely weeding and plant-protection measures are to be adopted. In dry areas and in calcareous and saline-alkaline soils, chlorosis is the major problem in dry nurseries. Seed treatment with FeSO4, the application of iron-chelates or spraying the nurseries with FeSO4 and flooding them gives some relief. However, in such areas, it is advisable to go in for wet nurseries. The seedlings obtained from the dry nurseries are generally hardy and establish themselves very fast when transplanted.
'Dapong' nursery. The 'dapong' method of nursery-raising consists in growing seedlings on a concrete floor or on a raised bed of soil covered with polythene sheets. This method is used especially in places where there is assured water-supply and when early transplanting is needed.
A small area is required for raising this type of nursery, 30-40 m2 being enough to raise seedlings for transplanting one hectare. The seedlings are ready after 14 days by using this method.
The preparation of land, if needed, is done essentially in the same way as in the case of the wet-bed method. Raised seedbeds are prepared after final levelling and are packed, levelled and covered with polythene sheets. Banana leaves, with their midribs removed, can also be used instead of polythene sheets. Pre-germinated seeds should be sown on top of these sheets at the rate of 1 kg of seed per square metre of the nursery. The germinating seeds are sprinkled with water and pressed down gently with hand or with a wooden flat board twice a day for the first 3-6 days. This helps the roots of the seedling to remain in contact with water retained on the surface and prevents drying. After six days, the seedbed could be irrigated up to a depth of 1-2 cm of water. The seedlings raised by using the 'dapong' method are then divided into convenient sizes and rolled like a material with roots outwards. It is necessary to control the water level in the main field transplanted with 'dapong'seedlings, as they are too small and are liable to be damaged very easily by letting in too much of standing water. The levelling of the fields is also very essential to avoid the stagnation of water and the mortality of the seedlings. Six to eight seedlings are placed in a hill. This method of nursery is also useful for raising a post-flood rice crop in Assam and West Bengal.
