On-farm measurements of nitrogen fixation by winter and summer legumes in the Hill and Terai regions of Nepal

Results are reported from on-farm surveys of N-2 fixation in Nepal, conducted between 1994 and 1999, involving the summer legumes soybean, mashbean and groundnut, and the winter legumes lentil and chickpea, at various locations in the Hill and Terai regions of Nepal. Additional less-detailed data were also collected for pigeonpea, grasspea and fababean. There were a total of 107 crops in the major and minor surveys. Estimates of the proportion of legume nitrogen (N) derived from N fixation (Pfix) were determined using the natural N-15 abundance method. Mean estimates of Pfix for the various species were 62% (soybean), 47% (mashbean), 57% (groundnut), 78% (lentil), 79% (chickpea), 75% (pigeonpea), 87% (grasspea) and 85% (fababean). Estimates of total N fixed (including roots) were 59 kg N ha(-1) (soybean), 28 kg N ha(-1) (mashbean), 153 kg N ha(-1) (groundnut), 72 kg N ha(-1) (lentil), 84 kg N ha(-1) (chickpea), 412 N ha(-1) (pigeonpea) and 80 N ha(-1) (grasspea and fababean). The on-farm measurements of N-2 fixation were generally similar to those of experimental crops in the same areas of the country. Correlation matrices of soil fertility parameters, shoot dry matter and N, and N-2 fixation revealed that the total amounts of N fixed were influenced primarily by crop growth. Based on the above figures, it was estimated that approximately 30,000 t N were fixed annually in Nepal by legumes, valued at US$ 15 million. (C) 2001 Elsevier Science B.V. All rights reserved.