Rice based cropping systems and nutrient demands

Rice based cropping systems and nutrient demands

Rice and rice based cropping systems (RBCS) (27.9 M ha) are the major contributing food production systems and also consuming major portion of all resources and inputs. Rice-wheat system cover largest area (9.80 M ha) followed by rice-rice (5.9 M ha.) and rice–fallow (4.4 M ha). Rice–wheat and rice-rice systems are followed in irrigated ecology while rice–lathyrus, rice-gram/pulse in rainfed uplands and lowlands (Rao et al.2008). Some of the important rice-based cropping systems under different agro-climatic zones of India are given in the Table. Future gains in food production have to come from RBCS which are already intensively cultivated with substantial nutrient flows.

Nutrient uptake by intensive cropping systems Nutrient removal by intensive cropping systems is required for developing future nutrient management strategies which vary substantially (Table). Rice–Wheat-Cowpea fodder system removes about 800 kg/ha. Annual removals of NPK could range from 440-815 kg/ha. Production of about 8-12 tons of grain/ha annually is associated with uptake of 140-330 kg N, 70-120 kg P2O5 and 200-390 kg K2O/ha which however could vary in space and time nutrient needs of individual crops while the efficiency of applied fertilizer nutrients largely depend on the quality of crop management. Exhaustive cropping systems cause mining of soil nutrients far in excess of external supply with consequent decline in soil quality and crop productivity. Application of N alone resulted in 33-129% depletion in soil P over 11 years in several intensive cropping systems (Nambiar and Ghosh, 1984). Similarly K removal in large quantities, sometimes more than N, can deplete non-exchangeable K under current levels of low K application. The net result in such systems has been perceptible decline in productivity growth, decreased responses to applied nutrients and declining soil quality as observed in many intensive cropping systems (DRR, 2008). It was attributed to decline in soil organic carbon content, reduced supply of nutrients such as N, K, Mn and S, decline in nutrient use efficiency, negative nutrient balance leading to depletion, decreasing quality soil and water resources and problems of pest/weed incidence.