Nutrient balances—a guide to improving sorghum- and groundnut-based dryland cropping systems in semi-arid tropical India

Information on soil-plant nutrient balance in India and elsewhere is scarce and mostly generalized. A review of earlier studies on nutrient balances was done to assess their relevance for researchers, policy makers, and farmers' understanding, to manage soil fertility for sustainable crop productivity. An on-farm nutrient balance study during 1995/1996 and 1996/1997 was designed to understand nutrient balances resulting from farmers’ practices in semi-arid tropical regions of India. This diagnostic study targeted sorghum-based cropping systems and groundnut-based cropping systems in low rainfall areas of the Indian SAT. Selection of farmers for this study was done through a systematic survey and analyses of factors effecting farmers' decision making for nutrient inputs. Intensive plot-specific nutrient input and output measurements were carried out on 53 farmers' fields for sorghum-based systems and 45 farmers' fields for groundnut-based system in this study. Topsoil mineral nitrogen (N) content observed in 2 years at the beginning of the crop season in two locations of Andhra Pradesh, India, was surprisingly high and exchangeable potassium (K) contents also indicated sufficient supply in most fields. Available phosphorus (P) in the majority of fields in both locations was around threshold levels, and just sufficient for most crops. The nutrient balance in sorghum-based systems indicates a moderate to higher negative balance of potassium leading to soil mining for potassium supply in these systems. Nitrogen and P balances were generally positive. Although the groundnut-based system accumulated 53% of its N requirements through BNF, negative balances of N and K were observed mainly due to low applications of these nutrients. Application of K along with options for improving BNF of groundnut are suggested. Better nodulating groundnut cultivars and efficient rhizobium strains need to be introduced. High positive balances were observed in the systems whenever commercial crops like castor and cotton were sown in the rotation. This indicates farmers' preferences for applying excess quantities of FYM to commercially important crops even in dryland farming systems. The replenishment costs of mined nutrients annually in different cropping systems were calculated based on current market prices of inorganic fertilizers.