Nitrous oxide emissions from rape field as affected by nitrogen fertilizer management: A case study in Central China

Agricultural soils are one of the major sources of atmospheric nitrous oxide (N2O) emission. Red soil, one of the typical agricultural soils in sub-tropical China, plays an important role in the global N2O flux emissions. To determine its N mineralization potential, a field study was conducted to assess the effect of application of nitrogen (N) fertilizer in a rape field under red soil at the experimental station of Heshengqiao at Xianning, Hubei, China. To estimate N-induced N2O flux, we examined N2O flux during the growth stages of the rape field including four treatments: fertilizer PK (N0), fertilizer NPK (60 kg N ha−1) (N1), fertilizer NPK (120 kg N ha−1) (N2), fertilizer NPK (240 kg N ha−1) (N3). There were distinct variations in soil N2O fluxes (from 0.16 to 0.90 kg N ha−1), with higher values being observed during the spring and autumn while low values were observed during winter season. Among different treatments, N fertilization significantly increased the N2O fluxes, with highest fluxes from N3 while lowest values being observed from N0 treatment. This suggested increased microbial activity in response to increased N fertilizer application. It was interesting to note that fertilizer-induced emissions decreased as the applied fertilizer amount was increased. During the whole growing season, N2O flux did not correlate with soil temperature, but it significantly correlated to other environmental variables; water-filled pore space (WFPS), soil NO3−–N and NH4+–N contents, which suggests the need for efficient water use and low inorganic nitrogen fertilizer management practices.