Rice is grown under varying ecosystems on a variety of soils under varying climatic and hydrological conditions ranging from waterlogged and poorly drained to well drained situations. Rice is also grown under rainfed as well as irrigated conditions (Fig 1.1).
The hydrologically based rice ecosystems terminologies to discriminate rice cultural systems in India include two subdivisions of irrigated rice (kharif and rabi) and three subdivisions of rainfed non irrigated rice (deep water, upland and lowland).
Different rice ecosystems of India are depicted in Fig 1.2.
Irrigated Rice:
Total area under irrigated rice is about 22.00 M ha, which accounts about 49.5 per cent of the total area under rice crop in the country. Rice is grown under irrigated conditions in the states of Punjab, Haryana, UP, Jammu & Kashmir, AP, TN, Sikkim, Karnataka, HP and Gujarat.
Rainfed Rice:
Rainfed ecosystem may be broadly classified into two categories:
Upland:
Upland rice areas lies in eastern zone comprising of Assam, Bihar, Eastern MP, Orissa, Eastern UP, WB and North-eastern hill region. In the rainfed upland rice, there is no standing water in the field after few hours of cessation of rain.
The total areas under upland rainfed rice in the country is about 6.00 M ha, which accounts for 13.5 per cent of the total area under rice crop in the country. The productivity of upland rice is very poor. As against the present national average productivity of about 2.13 t ha-1, the average yield of rice in upland areas in the country is only 0.90 t ha-1.
Lowland:
Lowland rice area is mostly located in the eastern region comprising of Assam, WB, Bihar, Orissa, Eastern MP and Eastern UP. Lowland rice area is about 14.4 M ha, which accounts for 32.4 per cent of the total area under rice crop in the country. Average productivity of rice in lowland areas ranges from 1.0 to 1.2 t ha-1 as against the national average productivity of 2.19 t ha-1.
Lowland rice may be further classified into three categories depending upon the standing depth of water in the field:
Shallow water:
The standing depth of water in the field is, generally, below 50 cm. Shallow rice area is located in the eastern states of Assam, Bihar, MP, Orissa, UP and WB.
Semideep water:
The standing depth of water in the field varies between 50-100 cm. These areas are lying in the eastern states of Assam, Bihar, MP, Orissa, UP and WB.
Deep water:
The standing depth of water is more than 100 cm in the field. Such deep water rice areas are mostly situated in the eastern states of Assam, Bihar, MP, Orissa, UP and WB. These areas are subjected to flood occurrence and duration of flooding varies from year to year.
Coastal Saline:
The coastal area is always subjected to salinity problem and these areas are situated in WB, Orissa, AP, TN and Kerala. Total area under coastal saline rice in the country is estimated at about 1.0 M ha which accounts for 2.3 per cent of total area under rice in the country.
Average yield in costal saline area is about 1.25 t ha-1 as against the average national yield of 2.19 t ha-1. Coastal saline soils are often affected with deficiency of ferrous and zinc which causes chlorosis and reduced tillering.
Cold/Hill:
Such rice areas lies in the hill regions comprising of Jammu and Kashmir, Uttranchal and North-eastern hill states. Total area under rice in cold/hill region is estimated at about 1.0 M ha which accounts for 2.3 per cent of total area under rice in the country. The average yield is about 1.1t ha-1 as against the average national yield of 2.19 t ha-1.
Major problems of these areas are cold injuries, blast, drought spell and very short span of cropping seasons. Because of the rolling topography in these areas, rice is grown on bench terracing which limits the use of fertilisers and improved agronomical practices. In these areas, the crop is sometimes affected due to low temperature in the early stage and sometimes at the flowering times leading to sterility problems.
Rice Production Constraints in Major Ecosystems:
Rice yields in India fluctuate greatly in time and space on account of its cultivation under diverse weather, ecological and socioeconomic conditions. Of the 42 M ha of rice, 20 M ha (45%) are irrigated and the remaining 22 M ha are under fragile rainfed conditions, often affected by aberrations of monsoon. Rainfed ecologies predominate in eastern India and include lowlands (14 M ha) uplands (6.4 M ha) and flood prone areas (3.0 M ha).
Rice productivity in irrigated ecosystems ranges from 2.8 t ha-1 in Karnataka to 3.9 t ha-1 in Punjab. Rainfed ecologies of shallow lowland, flood prone and upland areas register average productivity of 1.6, 1.0 and 0.5 t ha-1, respectively. Yield gap between national demonstration average and national average is 0.6 t ha-1 in irrigated areas and 1.5 t ha-1 in rainfed areas. Constraints responsible for lower yields are principally technical and socioeconomic.
Major constraints in each rice ecosystems are indicated below:
Irrigated Rice:
1. Erratic monsoon, which delay in water availability from the sources of irrigation water (canals, wells, tanks) and hence delay in planting.
2. Degradation of soil due to rising groundwater table and salinity levels.
3. Changes in physicochemical soil properties and ensuing reduced nutrient supplying capacity.
4. Emerging problems of multi-nutrient deficiencies.
5. Severe incidence of pests and diseases.
6. Poor credit and marketing facilities.
Rainfed Upland Rice:
1. Erratic and often inadequate rainfall and lack of facilities for essential irrigation.
2. Fragile and impoverished soils because of erosion.
3. Soil acidity leading to phosphate fixation, Al and Mn toxicity.
4. Iron chlorosis in calcareous/alkaline soils.
5. Poor land preparation and inadequate stand establishment because of high tiller mortality.
6. Severe weed infestation.
7. Continued use of traditional varieties.
8. Inadequate use of fertilisers.
9. Severe incidence of blast, brown spot and termites.
Rainfed Shallow Lowland and Semi-flood prone rice:
1. Delayed monsoon, often resulting in delayed planting.
2. Accumulation of toxic decomposition products in poorly drained soils aggravating the problems of iron toxicity or sulphide injury.
3. Flash floods causing inundation and intermittent droughts which affect the crop at different stages of growth.
4. Poor tillering coupled with high seedling/tiller mortality.
5. Excessive weed growth under broadcast conditions coupled with inadequate weeding.
6. Inadequate and unbalanced use of fertilisers and other agro inputs.
7. Continued use of traditional low yielding varieties.
8. Incidence of bacterial blight, sheath blight, tungro virus, blast, sheath rot, stem borer etc.
9. Non availability of inputs in time.
Flood prone Rice:
Lack of appropriate high yielding varieties possessing tolerance to drought during seedling phase and submergence with rising water level later as well as resistance to stem borer and sheath blight.