Nutrient Use Efficiency in Rainfed Agro–ecosystems: Concepts, Computations and Improvement Interventions

Abstract

Most agricultural soils in India have low native fertility. Successful and sustained crop production on these soils requires regular nutrient inputs through chemical fertilizers and/or organic manures to replenish soil nutrient reserves depleted by crop removal and other losses. It is essential to recognize that even in rainfed production systems with relatively low productivity level, the quantity of nutrient removal is quite substantial and exceeds addition. Furthermore, the quantum of nutrients available for recycling via crop residues and animal manures is grossly inadequate to compensate for the amounts removed in crop production. Thus, mineral fertilizers have come to play a key role in areas with low fertility soils, where increased agricultural production is required to meet growing food demand. Chemical fertilizers as source of plant nutrients are considered as the major contributor to enhancing crop production and maintaining soil productivity. Over the last 35 years, additional nutrients applied as manufactured fertilizers have been responsible for about 50 per cent of the yield increases in developing countries including India. Though the consumption of chemical fertilizers in India increased steadily over the years, the use efficiency of nutrients applied as fertilizers continues to remain awfully low (40-50% for N, 20-25% for P and 2-5% for Zn, Fe & Cu) owing to nutrient losses from the soils or conversion of nutrients into slowly cycling/recalcitrant pools within the soil. Further, at national level the partial factor productivity (PFPf) and incremental use efficiency (IUEf) of fertilizers used in food grain production have been gradually declining over the years (Fig. 1). This has become a matter of great concern and a challenge to be addressed on priority. India’s National Agricultural Policy lays much emphasis on enhancing use efficiency of agricultural inputs of which fertilizers represent an important and expensive component. When nutrient inputs are used inefficiently both cost of cultivation and threat for biosphere pollution increase. Thus, economic and ecological considerations highlight the compulsive need for more efficient use of nutrients in crop production.