RICE SOILS AND RELATED CONSTRAINTS IN RICE PRODUCTION

RICE SOILS AND RELATED CONSTRAINTS IN RICE PRODUCTION

More than 15 major soil groups of diverse characteristics are cropped to rice under different ecosystems (rain fed upland to deep water and irrigated), and agro climatic conditions. The crop is grown in 11 out of 15 agro climatic zones (west and eastern Himalayas, IGP, major portion of southern and eastern plateau region, eastern and western coastal region and the islands of Indian Ocean). Major soil types that are cropped to rice and rice based cropping systems listed in the Table suggest that predominantly alluvial soils, red and yellow loams, shallow to deep black soils and lateritic soils are cultivated to rice. More than 50% of land area in the country is affected by various soil problems that influence the agricultural productivity. Rice having the largest area (~ 45.0 M.ha) in the country and the world is grown in a variety of soil types with wide range of characteristics. In brief, the soil characteristics vary widely from sandy loam to clay in texture; soil pH from 3.0-10.5; organic carbon from 0.2 to > 2.0%; cation exchange capacity (me/100g soil) from < 10.0 – 50.0; and very low to high available nutrient status.

Flooding and puddling of a soil brings about a series of physico-chemical changes, the intensity and extent of this change depend, however, on the initial soil characteristics before flooding. The unique system followed for rice cultivation to facilitate rice roots to access plant nutrients, for effective weed control and to reduce percolation loss of water, has many beneficial effects of general amelioration of chemical fertility, increased availability of nutrients like N, P, K, Ca, Mn, Fe, Si, etc, preferential accumulation of organic matter and biological N fixation, reduced toxicity of Al and Mn, while availability of sulfur (S) may be reduced due sulfate reduction. Flooding soil is a great pH neutralizer. In problem soils this neutralizes acidity and alkalinity thereby influencing favorably to an extent in the release and availability of plant nutrients. On the contrary, the electro-chemical changes upon flooding could also lead to release of certain nutrients into toxic levels (Fe, H2S toxicity), and deficiency of micronutrients like Zn, Cu etc while the physical changes could constrain establishment and nutrition of non rice crops in the cropping system. Also, submerged soils with high organic matter content or added fresh crop / organic residues may lead to production of organic acids and sulfide, which can be toxic to rice plant (Kyuma, 2004). As rice and rice based cropping systems contribute largely to the total food production, sustainability of this system is vital for food and nutritional security. Further, water shortage being experienced in the country is threatening the conventional rice cultivation system warranting a re-look into the current practices and design strategies for enhancing resource quality and water productivity.

Because of its wide adaptability to diverse soil types and conditions including problem soils (for its beneficial effects during soil amelioration) the crop encounters a variety of field problems which is further aggravated by improper and inefficient management of resources and inputs. Important soil and management related constraints / problems encountered in rice production in India are listed below

Soil and management related constraints in rice production in India

 Increasing area under soil salinization (8-10 M ha) (salt affected) - major portion is      cropped to rice,  About 15 M.ha of rice soils are acidic associated with toxicity of Fe, Al, Mn, As,      deficiency of K, Ca, Mg, B, Si, and P fixation,  About 8.0 M.ha of rice area is deficient in zinc (Zn)  Nearly 50 and 80% of Indian soils are responsive (low to medium) to potassium and      phosphorous, respectively,  Blanket fertilizer management/recommendation over large domains,  Nutrient depletion (N, K, S) and loss of soil organic matter in intensive cropping      systems,  About 3.0 M ha in northwestern states under rice-wheat cropping system affected by      Mn deficiency  Nutrient problems of deficiency of N, P, K, Zn, Fe, S, Ca, B, and toxicity of Fe, Al, H2      S, As, Se and  Overall stagnation or deceleration of growth in productivity of crops and cropping      systems  Wet season rice followed by dry season fallow causes considerable buildup of nitrate in      soil profiles. This NO3 gets lost from the soil when fields are reflodded and puddled      for planting rice in the following wet season  Data indicate that iron (Fe) content of ground water in all the districts is high due to      high content of Fe-bearing minerals in soils, and such ground water is not suitable for      irrigation unless properly managed Continuous use of such irrigation water causes Fe-      toxicity and other nutrient imbalances in crop plants. It also greatly reduces P-     availability in the soil. Precipitation of iron in surface and subsurface layers may clog      the pores of the soils. As a result, drainage is impeded and crop plants suffer from      inadequate O2 supply in the root zone.

While the diversity in agro ecological environment in the country provide opportunities for growing numerous commercially viable cropping and farming systems towards a robust agriculture, efficient and sustainable management of natural resources especially soil and water for enhanced soil productivity is vital for over all economy of the country. Although soil productivity depends largely on a number of its diverse physico - chemical and biological characteristics, the ultimate output is governed by the precise agronomic operations, matching production systems with land capability, efficient management of external inputs like seed, water, nutrient etc., and maintaining a synergy between conservation and exploitation of resources such as soil and water.