Broadly, there are two main systems of cultivation of rice, the dry system, in which the crop is grown on dry field during rainy season, very much in the same way as other cereals and the wet (lowland) system, in which the land is inundated and the crop is grown in water from planting until harvest approaches. The principal systems followed in India are dry, semi-dry and wet.
Wet (Irrigated) System:
The wet system is also known as irrigated rice. In this system, the crop is grown under wet (irrigated) conditions from seed to seed. The field is brought to a soft puddle by repeated ploughings with 5-7 cm standing water. After obtaining a soft puddle and perfect leveling, rice seedlings are transplanted or sprouted seeds dibbled or broadcasted on the puddle.
Irrigated rice (wet rice system) area constitutes about 48 per cent of the total rice area (42 M ha) in India. Rice crop receive assured irrigation water through canals, tanks, wells etc. This irrigated rice contributes to 55 per cent of the total rice production.
Rice Nursery:
An alternative to broadcasting or drilling is to raise seedlings in a nursery to be transplanted in the main field when they have attained sufficient development. The nursery may be situated on dry-land or in a wet (irrigated) situation. Main difference between the dry and wet nursery is that the seedlings may remain in the former for as long as three months before transplanting, whereas seedlings from wet nursery must be transplanted within 25-40 days, depending on the duration of the cultivar.
In case where rainfall or water supply is precarious it is, therefore, an advantage to be able to postpone transplanting till the conditions are favourable for transplanting in the main field. Seedling can be raised by three methods.
Dry nursery:
In regions of non-assured water supply, where there is no scope for wet nursery, dry nursery is common practice. Soil moisture retentive land is ploughed thoroughly for obtaining a fine tilth and raised beds of 4-5 cm height, 1.0-1.5 m width and of convenient length are prepared, keeping 30 cm wide channels in between. Form yard manure around 10 t ha-1 is usually applied and incorporated 2-3 weeks before sowing. Dry seed is sown on the beds with adequate moisture, either broadcast or in close lines.
The seed is usually covered with a thin layer of soil or compost. Nursery beds are irrigated by sprinkling water periodically once in 2-3 days, depending on the soil and weather. Timely weeding and plant protection are adopted. In calcareous and saline- alkaline soils, chlorosis is the major problem in dry nurseries. Seed treatment with Fe SO4, application of iron chelates or Fe SO4 spraying and flooding the seedbeds can give reasonable relief. Seedlings obtained from dry nurseries are, generally, hardy and establish very fast when transplanted.
Wet nursery:
Nursery land is ploughed twice in dry condition and puddled subsequently by ploughing in 5-6 cm standing water three to four times, preferably at intervals of a week. Farm yard manure, compost or green manure at 10 t ha-1 is applied during first puddling. The field is leveled after final puddling and made into raised beds as under dry nursery.
Sprouted seeds are broadcast on soft puddle with a thin film of standing water. Till the seed germinate and the coleoptile turn green, only a very thin film of water or soil situation is maintained. Depth of standing water is gradually raised and maintained at 2-3 cm.
Depending on the nature soil fertility, it is advisable to fertilise seedbeds with 0.5 to 1.0 kgN, 0.5 kg P2O5 and 0.5 kg K2O for every 100 m2 area of the nursery before final leveling of the nursery beds. During rabi, when the temperatures are low, it is desirable to apply slightly higher dose of P2O5 to promote root development and to establish good stand in the nursery.
Timely plant protection and weed control is a must for healthy seedlings. When the seedlings are at 4-5 leaf stage, they can be uprooted without damage to the roots for transplanting in the main field.
The nursery area required to provide seedlings for transplanting one ha is roughly one-tenth of an ha and the seed rate is 40-50 kg ha-1. Healthy seed should be soaked for 24 hrs in clean water. The seed is then removed from the water and incubated in a warm, moist place for about 48 hrs for sprouting.
In some areas, semi-dry nursery is also practiced. It is almost similar to dry nursery, except that the nursery beds are irrigated before sowing and after sowing depending on the necessity. If irrigation water is available, it will be converted into a wet nursery, a week or two before uprooting the seedlings from nursery bed.
Depog Nursery:
In this method, nursery is grown on a concrete floor or on raised beds of soil covered with polythene sheets. This method is usually followed in places where there is assured water supply and when early transplanting is needed. A small area of 30-40 m2 is adequate to raise seedlings for transplanting one ha. With this method, the seedlings are ready for transplantation in 14-16 days after seeding.
Raised seedbeds are prepared after final land leveling and compaction. The beds are covered with polythene sheets or midrib removed banana leaves. Pregerminated seeds should be sown on top of these sheets at 1.0 kg seed m2 of the nursery. The germinating seed 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 to help the roots of seedlings to remain in contact with water on the surface and prevent drying.
After six days, seedbeds could be irrigated up to a depth of 1 -2 cm water. Seedlings raised with this method are then divided into convenient sizes and rolled like a mat with roots outwards. Four to six seedlings are placed in a hill in the main filed. A shallow depth of land submergence (2 cm) is necessary to avoid seedling mortality, as the small seedlings are liable to be damaged by deep land submergence during establishment in the main field.
In parts of western India, a specialised method of seedbed preparation is practiced, known as rab. The method consists in burning the seedbed and is practiced from Nerbudda in the north to Kanara in the south where equality of rice is important. This area is characterised by very heavy soils, which are sticky when moist and very hard on drying.
The seedbed is covered with a layer of cow dung superimposed with a layer of branches and other combustible matter, the whole being covered with a layer of soil. Burning is done shortly before rains are expected, after which the bed is thoroughly cultivated and seeds sown. Crop raised with the seedlings is said to produce the finest crop, which is used for seed purpose.
Transplanting:
The usual practice in most countries is to pull the seedlings, tie them into bundles of convenient size for handling, the roots being rinsed in water to remove soil. Top few cm of leaves are cut off to reduce evaporating surface and give rigidity to the plants, so that when transplanted the leaves do not bend over into the water.
In parts of south India, seedling bundles are arranged in a circular heap with roots exposed for 3-4 days. The bundles are than left in water for a night before planting. The object is to destroy by fermentation eggs and pests. Seedlings treated in this way are said to regain their green color quickly and be more free from inject pests than are unheaped seedlings.
Time of transplanting:
Planting time has significant influence on grain yield of rice. In general, transplanting in the first fortnight of July gives best yield in kharif. Delay in planting by 15-20 days from July 16 reduced grain yield by 15-20 per cent and two months delay by 50-75 per cent at several places. In northwestern India, June planting is ideal. Planting beyond June exposes the crop to low temperature at flowering (last week of August to first week of September) leading to low yields than earlier planted crop in June.
In warmer regions of south India, rice can be transplanted up to third week of July without significant reduction in yield. Delayed planting beyond third week by 10 and 20 days, however, reduced the grain yield by 15 and 35 per cent, respectively. Last week of December to middle of January is the optimum planting time for rabi rice.
Recommended planting times (ANGRAU) in Andhra Pradesh are given below:
It appears that the above recommended planting times are based on the availability of irrigation water in canals and rainfed tanks for planting. However, optimum planting time for kharif rice is much earlier if the source of irrigation water is wells (before mid-July). For summer crop under well irrigation, optimum planting time is April after rabi rice crop.
Age of seedlings:
Optimum age of seedlings for transplanting largely depends on the duration of the variety, system of raising nursery, soil fertility and other management practices. As a rule, for ordinary guidance, the practice of allowing one week for the seedlings for every one month of the maturity period of the particular variety is adopted.
At Hyderabad (AP), medium duration varieties gave significantly higher grain yields with young seedlings of 25 days old compared with seedlings of 35 and 45 days old when planted early in the kharif (Reddy and Reddy 1992). At higher nitrogen levels, however, 35 days old seedlings gave similar yields as that of 25 days old seedlings.
At Pusa (Bihar), medium and long duration varieties recorded higher yields with 30 days old seedlings. At Hyderabad (AP) also, long duration (165 days) MTU 5253 rice gave highest yield with 30 days old seedlings compared with 45 and 60 days old seedlings when planted in time during kharif. When the plantings were delayed beyond July, 35-45 days old seedlings performed much better than 25 days old seedlings in the case of Sonamashuri of medium duration (140 days).
Difference in yield due to 25, 35 and 45 days old seedlings was not significant when planted early in the season. From the results of experiments, it can be concluded that transplanting 25-30 days old seedlings in time is ideal in kharif while 45-60 days old seedlings are equally ideal during rabi. If plantings are delayed, aged seedlings are ideal during both the seasons.
When irrigation water is not available for timely transplanting, farmers resort to late planting beyond the optimum time. Under such conditions, economically viable yield many not be possible without special measures to compensate for the loss due to delay in planting. Experimental results are inconclusive in this aspect.
From the available information and with the author’s field experience, it can be said that for late planting, aged seedlings are better than younger seedlings irrespective of the duration of the varieties. The adverse effect of delayed planting with aged seedlings can be minimised to some extent by increasing the plant population and slightly enhancing the recommended rate of nitrogen (20 %) application.
Methods of transplanting:
Square planting is considered to be better than other planting patterns because of better use of natural resources. However, rectangular planting pattern seems to be more convenient for manual planting than square pattern. It also provides inter-row spacing for intercultivation with hand tools. The traditional method is characterised by planting the seedlings at about 20 x 25 cm apart at random in the field. About 90 per cent of the lowland rice fields in southeast Asian countries is planted in random fashion.
Skip-row planting has been found to perform better than conventional planting. Three rows at spacing of 10 cm followed by a gap of 30 cm gave 23 per cent higher yield at Bihar then normal planting with 20 cm row spacing. However, skipping every fourth row with 20 x 10 cm gave similar yield as that of normal planting with 20 x 10 cm at Cuttack. Skip-row planting aids in BPH management, where alleys are required for facilitating pest control.
Two to three seedlings per hill are enough both for traditional and improved Indica varieties under different rice ecosystems. However, 4 to 6 seedlings per hill appear to be idea if over-aged seedlings are used for planting. In the case of hybrids, two seedlings per hill is optimum during kharif. There may not be much difference in grain yield due to one and two seedlings per hill during rabi.
Spacing:
Spacing depends on season, duration of the variety, age of seedlings and soil fertility. In general, spacing should be wider in kharif than in rabi, wider in fertile soils than in poor soils, wider for high tillering, tall, leafy and lodging varieties than for low tillering, dwarf, less leafy and lodging tolerant varieties, wider for late varieties than for early varieties and wider for normal seedlings than for aged seedlings.
Summarising the results of AICRIP, Rao (1969) reported that a spacing of 20 x 15 cm is optimum in kharif and 15 x 10 cm in rabi. In Orissa, there was no difference in yield due to 15 x 10 and 15 x 15 cm during rabi. At Hyderabad (AP), 15 x 15 and 15 x 10 cm spacings were equally good for medium duration varieties during kharif.
In Tamil Nadu, yields of IR 50 and IR 64 did not vary significantly due to spacings of 15 x 10, 12.5 x 10.0 and 10 x 10 cm during both wet and dry seasons. Recommended spacings in Andhra Pradesh are 20 x 10, 15 x 15 and 15 x 10 cm for long, medium and short duration varieties respectively.
In general, spacings of 20 x 10 or 20 x 15 cm for kharif and 15 x 10 or 15 x 15 cm for rabi rice appears to be ideal under different rice ecosystems. Profuse tillering at wider spacings can compensate for low crop stand at planting. Rice crop shows high degree of plasticity to variations in spacing because of tillering. As such, there is no optimum plant population for any variety or season, except a range of plant population within which there may not be much significant variation in grain yield.
Double transplanting:
In this method, seeds are first thickly sown in the nursery and then 30-40 days old seedlings are transplanted in bunches with close spacing in a second nursery. Subsequently, these plants with tillers are uprooted, tillers separated and planted in the main field in about a month’s time. This practice is adopted in certain tracts of Andhra Pradesh, Tamil Nadu Maharashtra, Uttar Pradesh and Bihar where early planting is not feasible or results in excess vegetative growth due to high soil fertility or where it is desirable to hasten flowering for early harvest or where more efficient weed control is necessary.
Field trials at CRRI, Cuttack indicated that double transplanting with clonal tillers uprooted from 40-60 days old crop was better than planting with aged seedlings directly from nursery. This can be adopted as a mid-season correction against damage to previously established crop due to floods. Removing 25 to 50 per cent tillers from 20-40 days transplanted crop causes no adverse effect on its performance.
In a recent study at CRRI, Cuttack, crop stand following removal of 25 or 50 per cent tillers from direct sown crop resulted in comparable yield with undisturbed stand, which was however, higher than the stand devoid of 75 per cent tillers (Table 1.13). Regarding transplanted crop, comparable grain yield was obtained at the stand established with vegetative (clonal) tillers either from 50 or 75 per cent of its removal.
Direct Seeding of Sprouted Seed:
Transplanting has been the traditional practice of establishing irrigated rice in spite of huge labor requirement for uprooting and planting in the main field. Direct seeding of sprouted seed has been claimed in the recent past as an economically viable alternative to transplanting, provided perfect land leveling and control over irrigation water is ensured.
The land is prepared as for transplanted crop, however, with utmost care in leveling the field. Sprouted seed is broadcasted, dibbled in rows or drilled into the puddled soil. Since, the preference for direct seeding is reduced cost compared with transplanting for establishing the crop, it is desirable to go for drilling the seed than dibbling. Shallow depth of land submergence is necessary for 3-4 days to establish adequate crop stand.
This method may be advantageous in areas of shortage of labour for planting rice or where the labour wages are high and where mechanical seeders are available. If optimum crop establishment could be achieved, direct seeding of sprouted seed into piddled soil may be as good as or even better than transplanting, provided desired level of weed control can be achieved with minimum expenditure. Location specific recommendations may be appropriate than general recommendation in favour of direct seeding of sprouted seed on puddled soil.
Direct Seeding Sprouted Seed Vs. Transplanting:
There is uncertainty as to whether transplanting rice results in higher yield or whether it is justified only by enabling the land to carry more than one crop per year and by assisting to maintain the field reasonably free from weeds. Experimental evidence suggests that grain yields are similar under direct seeding of sprouted seed and transplanting.
In the rice based intensive cropping systems involving three or more crops per annum, there is limited scope for direct seeding as the rice crop occupies relatively longer period in the main field in spite of its shorter duration by about a week. Water requirement for direct seeded rice is also relatively higher than that for transplanted crop. It is an accepted fact that transplanting has great potential for weed control.
When there is no significant difference in grain yield due to direct seeding and transplanting, increasing cost of transplanting may lead to serious consideration of direct seeding as a desirable alternative at least in areas with adequate and controlled irrigation. Although, machines are available to drill pre-germinated seed rice into puddled soil, broadcast method is most common. With broadcast seeding, weed control is a serious problem at low plant density.
It is often said that transplanted rice is a lazy man’s crop, indicating its relatively easy management. The weight of evidence throughout the rice areas of the world is that transplanting results in higher yield. It must be admitted that transplanting increases labour cost. If it can be overcome, or circumvented by the use of mechanical transplanters, transplanting may be the invariable practice in rice cultivation.
Sincere efforts on the part of researches resulted in formulating an ideal package of production practices for direct seeding of sprouted seed into puddled soil under the conditions of good control over irrigation water, especially under well-irrigation during rabi.
It is up to the fanning community to accept or reject the technology based on the problems associated with it in implementing the formulated production package and its economic viability under a given farming situation. Location specific problems including control over irrigation water, cropping intensity and the magnitude of economic advantage may alone dictate acceptance or rejection of the formulated package for direct seeding of sprouted seed into puddled soil.
Dry System:
Dry system (upland rice fields), whether bounded or unbounded, may have no standing water on the soil surface 48 hours after cessation of rain or irrigation. Such sites are, usually, characterised by an aerobic soil environment during the period of rice growth. The fields are sloppy or are flat on terraced or unterraced landforms. Because of topography and high internal drainage arising out of light texture and porosity of the soil, upland fields do not impound rainwater even for short periods of time.
The rice crop on these uplands is, generally, direct sown under dry condition in May-June and harvested in September-October. Upland rice occupies about 7.1 M ha. About 6.2 M ha of this area is present in eastern zone comprising of the states of West Bengal, Orissa, Assam, Bihar, eastern Madhya Pradesh, eastern Uttar Pradesh and the N-E hill region. The rainfall in this zone ranges from 1000 to 2000 mm or more.
Ifugao rice terraces system:
It is a holistic farming system in Philippines. When rain falls on rice growing region of Ifugao in Philippines, it enters an ingenious 2,000 year old farming system. Community managed forests on top of steep hills provide food, medicine, fuel wood, construction timber and wood for everything. Because they have been managed sustainably, the hilltops absorb rainwater and feed it into rice terraces built into the hillsides.
The terraces control rainwater that would otherwise cause severe flooding and erosion. The rice terraces act as water infiltration system and provide communities living in the vallies below with drinking water.
The system is based on ‘biorhythm’ technology, in which social, cultural and economic activities and periods of rice harvest, wine production and religious rituals all are homonised with the rhythm of climate – rainfall, temperature and relative humidity – and hydrology. Yet Ifugao culture is not frozen in the past. Needing higher incomes, the Ifugao have intercropped their woodlots with high value crops such as banana, coffee and citrus – wise changes that do not harm the area’s unique system. The system serves as an example for sustainable agriculture for rest of the world.
Semi-Dry System:
In the eastern India comprising of Assam, West Bengal, Bihar, Orissa, eastern Madhya Pradesh and eastern Uttar Pradesh, semidry rice crop (rainfed lowland rice) occupies more than 50 per cent of the total 28 M ha of rice area. The eastern region is characterised by high rainfall of 1000 to 2000 mm or more, received mostly during June-July to October-November.
In this system, seeds are sown in ploughed dry soil with monsoon rains. When the monsoon becomes active (45-60 DAS), rainwater is impounded in the field. The crop is then cross ploughed (beushening) and treated as wetland crop (land submergence) for further cultural operations. Beushening is a common practice in direct seeded lowland rice in Orissa, MP, Bihar and to a lesser extent in WB, Assam and UP to control weeds, optimise crop stand and to improve soil aeration.
It involves cross ploughing or running cono-weeder in between rows of the young rice crop, 4 to 6 weeks after sowing, with a light country plough in about 5 cm standing water once or twice depending on weed density and crop stand. If the weed growth is high, it is followed by planking. This operation is called ‘buesan’ in Orissa and ‘biyas’ in MP.
Due to this operation, the crop is weeded, thinned and gap-filled with the uprooted seedlings. This operation is called ‘khelua’ in some areas. Khelua is done immediately after beushening or within a week after beushening. The practice of beusheniug has been reported to reduce straw and increase grain yield by checking vegetative growth.
Based, largely, on the level of rainwater stagnation in rice fields, semidry systems are divided into:
1. Rainfed shallow lowland rice (favourable situation with < 30 cm deep water).
2. Unfavourable lowlands (depth of water 30-100 cm).
3. Deep water lowlands (depth of water >100 cm).
In coastal Malabar adjoining the backwaters, land for rice cultivation called kole cultivation is secured by a kind of reclamation called lake bottoms. Large stretches of low lying land become submerged during monsoon, resembling inland lakes. After the rains cease, water is pumped into the sea through channels.
These channels are put up every year and are formed by a pair of parallel embankments, the earth for which is brought from long distances and is kept in position and protected from breaking by means of stakes, mats, palm leaves etc. Rice fields are formed in the mud of these lake bottoms and irrigation is provided from water in the canal.
Aerobic Rice System:
Irrigated lowland rice has very low water use efficiency as it consumes 3,000 to 5,000 liters of water to produce one kg of rice. In view of dwindling irrigation water resources, alternate rice cultivation methods such as alternate wetting/drying method (AWD) of irrigation in puddled transplanted rice system and system of rice intensification (SRI-saturated/AWD) have been advocated to save scarce irrigation water.
However, savings in irrigation water (-20%) due to such systems are not significant as land preparation (puddling) and consequent maintenance of shallow submergence (2 cm) or soil saturation require huge amount of water. As such, it is imperative to develop alternative rice cultivation systems that require less water for rice production without significant reduction in grain yield.
It is in this contest that the term ‘aerobic rice’ has been coined. Cultivation of improved rice cultivars in direct sown, non-puddled, aerobic soils under irrigation is called aerobic rice system (ARS). In other words, cultivation of rice like any other irrigated crop (cereals, pulses, oilseeds, vegetables etc.,) without land puddling and maintaining the available soil moisture between 25 and 75 per cent depletion level, depending on the stage of crop growth, is known as aerobic rice system.
It differs from the existing rainfed upland rice production system in that the aerobic system receives supplemental irrigation during rainy season unlike the existing upland rice system. In the absence of supplemental irrigation to aerobic system, there is no difference in the productivity of the existing upland rice system and aerobic system. There is need for developing rice varieties, which can respond to supplemental irrigation during rainy season for the success of aerobic system.