Sustainable production requires balanced resource use and it is the management decisions at a household level that determine nutrient fluxes and the economic viability of enterprises. Traditionally, the agricultural systems of the mid-hills of Nepal have relied on the close integration of forestry, livestock husbandry and crop production but increasing population and other social changes are straining these systems. This paper uses diverse sources to determine a N balance for a hypothetical household and to assess the sustainability of current farming systems with respect to N. For a hypothetical household holding 1 ha of land with two-thirds of it rainfed hillside (bari-land) and one-third irrigated lowland (khet-land), the system is currently in balance with inputs across the boundary of about 26 kg N a-1 (mainly in fertilizer) and losses, excluding gases, of about 60 kg N a-1 (mainly in crop removal). Tree fodder and grasses are a major source of N (80 kg N a-1) to the household. A major pathway for the flow of N within the system is via the forage fed to livestock, and the subsequent application of manure to crops. Typically, manure and compost supply 100 kg N to crops (four times that supplied by fertilizer) and produce crops with a N content in grains of 36 kg N. The N losses via soil erosion are shown to be small but the losses via leaching and gases are largely unquantified. It is concluded that the use of tree fodder and forage from forest areas and grasses from terrace risers as animal feed ensures a net movement of N from non-agricultural land to agricultural land. The magnitude of this movement is not known, because the quantities of vegetation gathered from inside and outside the household boundaries are not known.
Agriculture, Ecosystems and Environment (2000) 79 (1) 61-72 [doi:10.1016/S0167-8809(99)00143-7]