Residual Effect of Nitrogen Fertilization on Nitrous Oxide Flux and Yield of Three Cowpea Varieties (Vigna unguiculata L.) in Rainfed Rice Fields

Abstract

Nitrogen fertilizer use in rainfed rice fields is generally less efficient, only part of N is taken up by plants for their gowth and other N is lost and fixed by soil particles. Nitrogen loss in the form of nitrous oxide can reduce N fertilizer use efficiency and contribute to the increase of atmospheric greenhouse gases emission. The field experiment was conducted to determine the residual effect of N fertilizer on nitrous oxide (N2O) flux and yield of some cowpea varieties (Vigna unguiculata) in rainfed rice fields. The experiment was arranged in a factorial randomized block design with three replicates. The first factor was three cowpea varieties (KT 9, KT 6, KT 3), while the second factor was four levels of residual inorganic N fertilizer (0, 90, 135, 180 kg N ha-1). The variables measured were N2O fluxes, grain yield, biomass weight, total N content in soil before planting cowpea, available N in soil after harvesting cowpea. Residual N fertilizer increased significantly N2O emission from cowpea cropping. Nitrous oxide emission from plots grown with cowpea variety of KT 9, KT 6, and KT 3 ranged 0.42-0.69, 0.30-2.64, and 0.09-2.19 kg N2O ha-1, respectively. N losses from soil grown with KT 9 was lower than those in plots grown with other varieties. Residual effect of N fertilizer increased available N in soil as much as 11.6-82.3% (KT 9), 7.6-30.6 % (KT 6), and 9.6-67.9% (KT 3), recpectively. Residual effect of N fertilizer increased significantly grain yield of KT 9, KT 6, and KT 3 varieties as much as 45.7-111.8%, 79.8-89.3%, and 6.9-25.4%, respectively.