| In order to understand the characteristics of nitrogen loss through different pathways under conventional fertilization conditions,a field experiment was conducted to investigate the variations of N2O emission,NH3 volatilization,N losses through surface runoff and leaching caused by the application of nitrogen fertilizers during summer maize and dry direct-seeding rice growing season in the Middle and Lower reaches of the Yangtze River,China.Results showed that,in the maize growing season,when compound fertilizer was used as basal fertilizer at the rate of 150 kg N-ha’1,and urea with the same level of fertilizing as topdressing,N2O emission coefficient in the entire growing season was 3.3%,NH3 volatilization loss rate was 10.2%,and nitrogen loss rate by leaching and surface runoff was 11.2%and 5.1%,respectively.In addition,leaching was the main pathway of nitrogen loss after basal fertilizer,while NH:3 volatilization and nitrogen leaching accounted for the majority of nitrogen loss after topdressing,which suggested that nitrogen loss from different pathways mainly depended on the type of nitrogen fertilizer.When maize needs topdressing,it appears to be effective to apply the new N fertilizer with low ammonia volatilization instead of urea to reduce N losses from N fertilizer.Similarly,in the rice growing season,when compound fertilizer was used as basal fertilizer at the rate of 162 kg N·ha-1,and urea at the rate of 108 kg N·ha-1 as topdressing,N2O emission coefficient in the entire growing season was 1.5%,NH3 volatilization loss rate was 9.7%,and NO3--N loss rate by leaching was 4.9%.Nitrogen loss rate by surface runoff was zero,due to no draining in the whole rice growing season.In this study,according to the soil type and climatic factors,the regions of China were divided into eight areas.Using the measured N2O emission,NH3 volatilization,total N runoff and leaching data and environmental factors from the papers,which were published in Chinese or English journals about rice,wheat,and maize from 2000 to 2012,and referring to the meteorological data from China Meteorological Data Sharing Service System,the models of N2O emission,NH3 volatilization,total N runoff and leaching data and the application rate of nitrogen fertilizer in each region were established.According to the mean application rate and the sown area of the rice,wheat and maize from each region,we estimated N2O emissions for the rice,wheat and maize season per year after 2000 were 41.73±13.67Gg,44.52±11.51Gg and 72.33 ± 11.65Gg,respectively;NH.volatilization were 1035.33±264.54Gg,31.28±81.13Gg and 951.71±144.03Gg,respectively;total N runoff were 263.75±60.14Gg,329.98±64.43Gg and 89.23±32.03Gg,respectively;total N leaching were 196.78±85.46Gg,213.77±76.63Gg and 938.62±91.24Gg,respectively.The annual average economic losses resulted from N2O emission for the rice,wheat,and maize season after 2000 were 1.73±0.57,1.84±0.48 and 3.36±0.54 billion yuan,respectively.Similarly,those from NH3 volatilization,total N leaching and total N runoff were 2.75±0.70,2.68±0.61 and 2.00±0.87 billion yuan for the rice season,0.88±0.22,3.35±0.65 and 2.17±0.77 billion yuan for the wheat season,2.53±0.38,0.90±0.32 and 9.52±0.93 billion yuan for the maize seaason,respectively. |
