Perspectives on nutrient management in arable farming systems

Sustainable nutrient management includes economizing on finite natural resources such as fossil energy and limited phosphorus (P) resources. Arable farms with exclusively crop production are characterized by large nutrient export in farm products. In the long term, nutrient export from soils and losses must be balanced by adequate inputs of fertilizers, biological N-2 fixation or recycled products from the human food system. Critical issues associated in particular with arable systems discussed in this paper include organic matter depletion and lack of synchronization between nitrogen (N) release from organic N pools (such as plant residues and green manures) and crop demand, leading to N losses and/or N deficiency. Further critical issues identified include efficient use of indigenous soil P and applied P fertilizers and, especially in organic systems, risk of depletion of P and K, which if realized reduce soil fertility and limit production. The risk of enrichment of trace elements to levels toxic to soil microbes, plants, animals or man is also discussed. Suggested measures for managing these critical issues include choice of crop rotation, residue and green manure management.