Mining of nutrients from the soil, particularly in developing countries, is a major problem, causing soil degradation and threatening long-term food production. This paper develops a methodology for carrying out nutrient audits, which includes the calculation of nutrient balances and an evaluation of trends in nutrient depletion/enrichment. Nutrient balances for arable farming are constructed for 197 countries for 1996 and for the world and two specific countries - a developed/enriching country (Japan) and a developing/depleting country (Kenya) for the period 1961 - 1996. The results indicate that nutrient efficiency is approximately 50% for N, 40% for P, and 75% for K. In some countries in Western Europe and in Japan and the Republic of Korea, with large, mixed farming systems, there is a surplus of N, P, and K. However, in almost all other countries, food production is currently dependent on depleting large quantities of nutrients from soil reserves and this is likely to continue. The world average soil depletion of nutrients in 1996 was estimated to be 12.1 kg N ha(-1), 4.5 kg P ha(-1), and 20.2 kg K ha(-1). The depletion of K is particularly severe and could ultimately lead to a serious loss of crop productivity in several countries. There is an urgent need to investigate this issue further. Analytical tools, such as the nutrient audit model described, can play an important role in assessing the problem, and in developing sustainable nutrient management policies, strategies, and practices.
