Nitrogen, phosphorus, and potassium budgets in Indian agriculture

Nutrient budgeting is a useful tool in determining present and future productivity of agricultural land as well as undesirable effects of nutrient mining and environmental pollution. Budgets of N, P, and K were calculated for India for 2000-2001 taking into consideration the inputs through inorganic fertilizer, animal manure, compost, green manure, leguminous fixation, non-leguminous fixation, crop residues, rain and irrigation water and outputs through crop uptake and losses through leaching, volatilization and denitrification. Inorganic fertilizer was the dominant source contributing 64% of N and 78% of P inputs in Indian agriculture, whereas K input through inorganic fertilizer was 26%. Removals of N, P, and K by major agricultural crops in the country were 7.7, 1.3 and 7.5 Mt, respectively. There were positive balances of N (1.4 Mt) and P (1.0 Mt) and a negative balance of K (3.3 Mt). It was projected that N, P, and K requirement by Indian agriculture would be 9.78, 1.57 and 9.52 Mt, respectively, to meet the food demand of 1.3 billion people by 2020. The study identified the 'hotspots' of excess nutrient loads as well as of nutrient mining regions in India to improve our ability to predict environmental degradation due to imbalanced fertilizer use. However, there are some uncertainties in India's nutrient budget and more research is required to reduce these uncertainties.