Agricultural intensification and the impacts on soil fertility in the Middle Mountains of Nepal

Agricultural intensification in the Nepalese Middle Mountains has caused concern that soil inputs are insufficient to meet the higher nutrient demands of increased crop rotations, that increased chemical fertilizer dependency will cause soil acidification, and that soil fertility will decline. To examine changes in soil fertility dynamics over time and between land-use groups soil samples, farm surveys, and nutrient budgets were determined for less intensive irrigated and rainfed sites in 1994 and for intensive irrigated and rainfed sites in 2000 in the Jhikhu Khola watershed. Changes in fertilizer policy and in cropping rotation (introduction of potatoes and tomatoes and a decline in the use of a pre-monsoon fallow) have contributed to unbalanced and inadequate soil nutrition. Farmers in 2000 used significantly more compost and fertilizer (particularly diammonium phosphate) than in 1994. In irrigated sites, a significant increase in available soil P, a significant decline in exchangeable soil K, and a decline in base cation content was observed in sites sampled in 2000 versus 1994. Farmers intensively cultivating irrigated land need to address exchangeable soil K deficits, while reducing excess P inputs and taking measures to reduce the potential for soil acidification. In contrast, intensive rainfed sites have large surpluses in N, P, and K budgets for sites sampled in 2000, with significant increases in soil K, base saturation, and available soil P between 1994 and 2000. Given current crop yields, soil inputs to rainfed sites could be reduced to minimize unnecessary economic expenditures and eutrophication problems without depleting the soil nutrient pool. Key words: Agricultural intensification, soil fertility, phosphorus, potassium