In this article we will discuss about the cropping systems of rice in India.
1. Dry Cropping Systems:
Various cropping systems involving mixed, inter and or sequence cropping, ideal for different rice ecosystems, have been identified by the farms and scientists to boost and stabilise the productivity.
Mixed Cropping of Rice Varieties:
In low lying areas of Assam, floods damage rice crop almost regularly during May and August. Floods, generally, damage summer or aus (March-June) and winter (July-November) rices. Sometimes, the deep water or boro rice (March-November) is also affected by floods during late September. To avoid risk of total crop loss, many fanners practice mixed cropping of early rice (ahu) with late maturing deep water (bao) rices in flood prone areas.
If flood occur early, the ahu rice is damaged, leaving the bao rice to survive and give up to 50 per cent of the expected produce. If the flood occurs late in September-October, the bao rice is damaged, while a good crop of early maturing rice has already been harvested. In case no floods occur, mixed cropping of ahu and bao rices in 1:1 ratio results in significantly higher yield than sole cropping of either ahu or bao rices.
Growing a mixture of autumn and winter varieties of rice called udo in Tamil Nadu and koottumundakan in Kerala is an age old low cost agronomic technology practice in low-lying waterlogged areas, where modern cultivation methods are not suitable. This system has a built-in advantage of low cost of cultivation as it eliminates cost of land preparation for planting winter crop.
In the koottumundakan system, a short duration autumn variety and a photosensitive long duration winter variety are mixed in 3:1 ratio and sown broadcast during April-May in fields prone to long period of waterlogging.
The winter variety gets a topping when the autumn variety is harvested during September whose stubbles are allowed to decompose. The stubbles of winter variety grow normally with good tillering, spread over the field and come to maturity in January.
Intercropping Rice with other Crops:
Upland rice can be intercropped with pulse crops, sesame, maize and other millets. Generally, greengram, blackgram, groundnut and pigeonpea are intercropped with every 3 or 4 rows of rice. In normal years, there will be yield advantage with intercropping, while the component crop gives reasonably good yield during the years of rice failure.
In dry rice dominant areas, important intercropping systems with rice are:
1. Rice + pigeonpea in 4:1 row proportion
2. Rice + groundnut in 4:2 row proportion
3. Rice + soybean in 4:1
4. Rice + pulse in 4:1
5. Rice + maize in 4: 1
6. Rice + sesame 4:1
Sequence Cropping:
Sequence cropping is possible in rainfed rice ecologies if the residual soil moisture is utilised properly by timely sowing of appropriate crops and cultivars. In rice growing areas of West Bengal, postmonsoon winter crops like rapeseed, mustard, lentil, gram, niger, peas, sunflower and safflower are remunerative.
In Bihar, sequence cropping with pigeonpea, or lentil in rainfed uplands and with sesame, sweet potato or rajmash in rainfed lowlands have been found profitable. Many farmers in eastern Uttar Pradesh grow a linseed crop from January to March, if the rice harvest is completed by December.
An exhaustive compilation of rice ecosystems research indicates the feasibility and prospects of the following rice based cropping system in rainfed lowlands.
2. Wet (Irrigated) Cropping Systems:
Assured irrigation water is the real potential for rice based intensive cropping systems. Major irrigated areas receive irrigation water only for a part of the year. In such areas, a single or two crops are raised with assured water supply. If facilities are available to lift groundwater, a third or even fourth crop is raised.
Thus, the cropping intensity in irrigated agriculture ranges from 100 to 400 per cent. There are innumerable rice based cropping systems in the country due to very widely varying differences in soil and climatic conditions under with different crops are grown.
As such, only major irrigated rice cropping systems are given below:
Relay Cropping:
In most places where only one rice crop is grown during wet season, a period of 2-3 months is, generally, available after the harvest of rice when soil contains reasonably adequate soil moisture for raising a short duration upland crop. However, sowing after rice harvest leads to soil moisture loss. Hence, relay cropping is practiced.
The upland crop is broadcasted into the standing rice 7- 10 days before its harvest. In Orissa, linseed, lentil, gram, peas, blackgram, greengram, lathyrus (khesari) have been found suitable as relay crops in rainfed lowlands. Broadcasting of soybean seed into standing rice crop, 2-4 days before harvest of rice crop has gained importance in the recent part.
3. Rice-Fish Farming System:
The CRRI, Cuttack, has developed rice based integrated farming system involving fish/prawn, vegetable and fruit crops. Rice-fish fanning comprises 2.5 m wide bunds raised to 1 m all around the main field and a water storage system in the form of 2 length-wise side trenches with gentle slope (0.5%) connecting a wide pond refuge at the lower end.
The net area covered by bunds and water storage system is maintained at 20 and 13 per cent respectively. The land use ratio between trenches and pond refuge should be 1: 1, keeping average depth of trenches 1 m and pond refuge 1.75 m. Cultural operations under this system involve growing of submergence tolerance rice cultivars like Panidhan, Tulasi, Utkalaprabha etc., under row dry seeding using 40 kg seed ha-1 during second fortnight of May, application of fertiliser at 40 N, 20 each P2 O5 and K2 O ha-1 at sowing and avoiding using plant protection chemicals.
Freshwater major carps (catla, rohu, mrigal) and common crap fingerlings are grown with juveniles of 2 giant prawn species in equal proportion, keeping 1 m-1. Fish species should include 30 per cent surface feeder, 29 per cent column feeder and 50 per cent bottom feeder. Fish stock should regularly be fed with oilcake and rice polish mixture at 2 per cent of the biomass besides regular manuring and liming of water body.
Winter crops like watermelon, vegetables, pulse crops etc., can be successfully raised after rice preferably on opposite side of the pond refuge. Besides, papaya, banana, okra etc., in rainy season, and radish, tomato, carrot, bean, cauliflower and cabbage in winter season can be raised on bunds to maximise the productivity. This system of rice fanning is found to be three times more productive and four times more economical than only rice-fish culture.
4. Nutrient Management in Cropping Systems:
Early experiments on nutrient needs pertained mainly to single crop. Hence, there was no scope in accounting for residual effects. From 1970s, research under Long Term Fertiliser Experiments and All India Coordinated Agronomic Research Project generated useful information for efficient use of fertilisers in different cropping systems.
Nitrogen:
In rice-wheat cropping system, both the crops in the sequence responded to 120 kg N ha-1 provided other limiting nutrients are adequately replenished. Although, considerable amount of nitrogen applied to rice crop is left in the soil, only a small fraction is recovered in succeeding crop. Since the recovery of nitrogen is very slow and spread to several succeeding crops, yield gain due to residual nitrogen is often negligible in cereals, particularly in rice based cropping systems.
In rice-potato sequence, 100 kg N ha-1 applied to either of the crops left residual effect equivalent to 25 and 33 per cent of its direct effect in potato and rice, respectively on alluvial soils of Kalyani. Reduction in fertiliser nitrogen demand of intensive cereal- cereal systems owing to inclusion of grain or forage legumes is now fairly established.
Phosphorus:
In rice-wheat system, wheat responds to applied phosphorus while relatively lower response was observed in lowland rice because of increased availability of phosphorus due to land submergence. Application of 60 kg P2O5 ha-1 to wheat in alluvial soils of Punjab was sufficient to meet the phosphorus requirements of both the crops in rice-wheat system.
However, later studies indicated superiority of direct application of 30 kg P2O5 ha-1 each to rice and wheat over 60 kg P2O5 ha-1 to either of the crops. In south Gujarat, where the phosphorus fixing capacity of soil is high, phosphatic fertilisers to wheat can be reduced to 50 per cent in rice-wheat system. Advantage of residual phosphorus to the succeeding crop in rice-wheat sequence is inconclusive.
Nevertheless, under resource constraints, phosphorus application to wheat may be preferred over rice in rice-wheat system on marginally deficit soils. All the crops in the system may require recommended rates of phosphorus application if the soils are deficient in phosphorus.
Potassium:
Long-term studies on cropping systems research showed progressive increase in response to potassium fertilisers in both rice and wheat crops in rice-wheat system. In jute growing areas, where rice-potato-jute is a common system, potato suffered more from potash deficiency. Application of potash to potato and allowing jute to meet its potash requirements through residual affect was beneficial. In rice-wheat-jute system also, jute was benefited from potash applied to rice and wheat.
Secondary and Micronutrients:
In rice-wheat system at Modipuram, application of 90 kg S ha-1 as gypsum to wheat or 45 kg S ha-1 each to rice and wheat in rice-wheat system was more beneficial compared to 90 kg S ha-1 to rice. Long term studies on residual effect of sulphur in cropping systems could not provide valid information as of now.
Nevertheless, available results provide a general guideline that sulphur use efficiency in cropping systems can be obtained to sulphur application to the high responsive crops and to a land management which conserves sulphur for the succeeding crops.
In the cropping systems involving non-rice crops, residual effect of zinc lasts for several crops grown in succession. However, duration of residual effect is curtailed with the inclusion of lowland rice in the cropping systems. Residual effect of 40-50 kg Zn ha-1 as Zn SO4 could be recorded only in succeeding wheat and not in subsequent third and fourth crops in Uttar Pradesh.
While application of 11 kg Zn ha-1 as Zn SO4 was optimum for two rice-wheat cycles on Zn deficient soils of Punjab, use of 10 kg Zn ha-1 to the first rice crop followed by either repeat application of 10 kg Zn after fourth crop or 5 kg Zn after these crops was ideal for rice-wheat system on calcareous soils of Bihar. In general, efficiency of zinc in cropping systems can be increased through application of organic manures.
In rice-wheat system, wheat suffered yield loss due to boron deficiency on acid sandy soils of West Bengal. On calcareous soils of north Bihar, application of 8 kg borax ha-1 each to rice and wheat was more beneficial than application of 16 kg borax to rice. More field data are necessary to formulate secondary and micronutrient strategies for cropping systems.