Some experiments were conducted in field conditions at Rampur, Nepal between 2001 and 2003 to assess the potential of wheat straw management with grain and green manure legumes in the lowland areas on soil N dynamics, crop yields and systems’ N balances. Two levels of wheat straw incorporation (0 and 2 Mg ha-1) with four types of land management (bare fallow control, mucuna, mungbean and maize) treatments were randomly allotted in the 10 m2 plots in the fields. When the land was left bare during the transition season, Nmin was initially building up of 50-80 kg of nitrate-N and subsequently lost by nitrate leaching and denitrification, resulting in low N uptake of rice. The application of wheat straw during DWT significantly reduced soil Nmin at the same rate as soil microbial biomass-N increased and resulted in <1 kg ha-1 of nitrate leaching and minimal nitrous oxide emissions from the soil. Growing cover crops during transition period reduced leaching losses by half and nitrous oxide emissions by two thirds of those in the bare fallow control, and BNF-N additions by legumes ranged from 27 to 56 kg ha-1. Depending on the type of legume, this resulted in increased crop N uptake and grain yield. The lower N benefits were associated with the grain legume because about 50% of the N assimilation was removed by grain harvest, while the high benefits were obtained with green manures. When DWT is sufficiently long, the cultivation of legumes appears economically and ecologically beneficial and should be encouraged. Combinations of straw amendment and green manure use during DWT provide the largest benefits in terms of grain yield, and N balance with possible long-term benefits for system’s productivity.
Key words: Soil, nutrient management, lowland rice
J. Inst. Agric. Anim. Sci. 27:139-147 (2006)
Nitrous Oxide Emissions from a Sugarcane Field with Green Manure and Chemical Fertilizer Applications in Okinawa, Japan