Nitrous Oxide Emissions from Spring-maize Field Under the Application of Different Nitrogen and Phosphorus Fertilizers

Excessive fertilizer application to cropland results in high N2O emissions, cropland becomes an important source of greenhouse gas(GHG) emission. In order to reduce N2O emissions, this study investigated the effects of fertilizer types on N2O emissions in spring maize field in northern China, which was monitored continuously by automatic measurement system. The responses of grain yield, in addition to N2O emissions, were examined to explore feasible strategies to reduce N2O emission. Four fertilization management practices were selected, viz.(1)zero fertilizer as control treatment(CK),(2)urea treatment(U),(3)urea and phosphorus treatment(NP) and (4)nitric phosphate treatment(NOP). The results indicated that the total N2O fluxes under each treatment were CK:0.21 kg N·hm-2,U:1.19 kg N·hm-2,NP:0.93 kg N·hm-2,NOP:0.69 kg N·hm-2 respectively. The N2O emissions were mainly influenced by fertilization, irrigation, precipitation and soil temperature. Soil N2O uptake was observed during the later growth stage of spring maize when the soil mineral N was lower than 7 mg N·kg-1. The N2O emission factor(EF) of every fertilizer treatment was lower than 1% which was suggested by the Intergovernmental Panel on Climate Change(IPCC). This meaned the default EF of IPCC should not be used for estimation of the regional N2O fluxes in spring maize field in northern China. Phosphorus fertilizer not only could reduce the N2O emissions but also increase maize grain yield, whereas nitric phosphate was significantly more effective than urea in reducing the N2O emissions. Evaluation based on crop yield and N2O emissions showed that NOP treatment was a better management practice in the sense that, when compared to U and NP treatments, it reduced not only N2O emission by 42% and 26% separately, but also farmers′ expenditure on fertilizers by 15% and 30%, while maintaining crop yield.