Nitrogen Fertilization Management and Nitrous Oxide Emission in Lettuce Vegetable Fields in Central Vietnam

Vegetable production with high N inputs is a potential source of greenhouse gas emission and N2O from soils. However, in Central Vietnam, high rates of N fertilization on sandy soils may not generate much N2O by denitrification due to limited anoxia. This study was carried out to evaluate the impact of four N fertilizer rates including: 0, 30, 60 and 90 kg N ha(-1) and three N fertilizer forms supplied as urea, ammonium sulfate and calcium nitrate on the yield of lettuce and the N2O emission from loam and deep sandy soils in two crop seasons from January to April, 2015. The increase in the cumulative N2O emission and the yield based N2O intensity is proportional to the increase in N fertilizer application. Calcium nitrate fertilizer application at rate of 90 kg N ha(-1) had the highest N2O emission as compared with ammonium sulfate and urea fertilizers application, which raised more than 1.20 to 1.82 times (ammonium sulfate) and 1.60 to 1.91 times (urea) in loam and deep sandy soils, respectively. Compared to the N-90 treatment, N2O emission of N-60 was reduced by 42% in loam soil and 30% in deep sandy soil without decreasing crop yield. The growing season emission factors (EFgs) were 0.40% to 0.61% of added N, emitted as N2O and increased with N fertilizer application rate. N2O fluxes reduced as the amount of applied N-fertilizer decreased significantly. (C) 2018 Friends Science Publishers