One Two




The rice-wheat annual double cropping system (R-W) is the most important food crop production system of Nepal and occupies some 0.5 million ha in the Himalayan foothills of the country. A main production constraint is N deficiency. Mineral N fertilizer use in the predominant small-holder agriculture is low and crops rely largely on native soil N for their nutrition. Continuous removal of crop residues results in low soil organic matter contents and hence low soil N supplying capacity. Alternating soil drying and wetting cycles stimulate N losses. This is likely to be most severe during the 3-month dry-to-wet season transition period (DWT) after the harvest of wheat and before the transplanting of rice. Managing native soil N, particularly during DWT, is thus essential to sustain R-W productivity. We hypothesize that an improved understanding of native soil N mineralization and loss dynamics will allow the development of soil and crop management systems that increase N use efficiency and productivity of low-input small-holder R-W systems of Nepal. The project objectives are
• Quantify soil Nmin dynamics during the dry-to-wet season transition period (aerobic soil) and the rice cropping season (anaerobic soil) in pot and laboratory incubation experiments
• Evaluate the effects of of temporary N immobilization by (1) wheat straw residue return and (2) nitrate catch crops on N losses during the dry-to-wet season transition period in pot experiment in the greenhouse
• Validate the findings on native soil N dynamics and their effect on N use efficiency in the fiel