Nitrogen Fertilizer Demand And Greenhouse Gas Mitigation Potential Under Nitrogen Limiting Conditions For Chinese Agriculture Production

The use of nitrogen fertilizer is critical to feeding China’s hungry. However, the excessive use of chemical N fertilizers in agriculture, resulting in a large number of environmental problems. Therefore, limiting the N fertilizer rate is urgent to ensure national food security and protect resources and environment. This thesis focuses on the current situation of China’s agricultural nitrogen fertilizer application based on the analysis of farmer survey data and statistical data. A regional N management approach was developed based on the cost of the agricultural response to N application rates from large number on-farm experiments to optimize N management across each agroecological subregions in the intensive Chinese smallholder wheat, maize and rice belt. We also compared N rate, grain yield and GHG emissions between the regional N management approach and farmers’ N management, and evaluated the potential for increasing grain yields and mitigating GHG emission intensity using this regional N management approach when compared to farmers’ practices across each region. The regional optimal N rate of cash crops, vegetables and fruits was also evaluated by data mining method. Then the demand of N fertilizer was forecasted based on regional optimal N rate and crop cultivated area. Main results as below:1. We present a new database of N input from a survey of32219farmers during2007to2009. Across all farmers, the N application rate of wheat, rice and maize was210,210and220kg ha-1, respectively. The N application rate of vegetables and fruits was388and555kg ha-1, respectively. The proportion of nitrogen fertilizer consumed by wheat, rice, maize, vegetables, fruits, oil crops, potatos, tea garden, beans and other crops was14%,16%,19%,20%,15%,5%,4%,2%,1%and4%, respectively.2. In this study, a regional N management approach was developed based on the cost of the agricultural response to N application rates from1,165on-farm experiments to optimize N management across7agroecological subregions in the intensive Chinese smallholder wheat belt. The calculated regional N rate was174kg N ha-1. The corresponding grain yield averaged6.24Mg ha-1. Calculated GHG emission intensity, weighted by wheat area in each subregion, averaged495kg CO2eq Mg-1grain. This regional N management approach, if widely adopted in China, could reduce fertilizer N consumption85MT, increase Chinese wheat production1160MT, and reduce total GHG emissions1040MT.3. In this study, a regional N management approach was developed based on the cost of the agricultural response to N application rates from1,726on-farm experiments to optimize N management across12agroecological subregions in the intensive Chinese smallholder maize belt. The calculated regional N rate was174kg N ha-1and ranged from150kg N ha-1(NE1&NE2) to219kg N ha-1(NW3). The corresponding grain yield averaged8.56Mg ha-1. Calculated GHG emission intensity, weighted by maize area in each subregion, averaged334kg CO2eq Mg-1grain. This regional N management approach, if widely adopted in China, could reduce fertilizer N consumption143MT, increase Chinese maize production3190MT, and reduce total GHG emissions1860MT.4. In this study, a regional N management approach was developed based on the cost of the agricultural response to N application rates from1,177on-farm experiments to optimize N management across8agroecological subregions in the intensive Chinese smallholder rice belt. The calculated regional N rate was167kg N ha-1and ranged from114kg N ha-1(NE) to224kg N ha-1(LYR). The corresponding grain yield averaged7.67Mg ha-1. Calculated GHG emission intensity, weighted by rice area in each subregion, averaged1236kg CO2eq Mg-1grain. This regional N management approach, if widely adopted in China, could reduce fertilizer N consumption125MT, increase Chinese maize production1536MT, and reduce total GHG emissions1290MT.5. The demand for agricultural N fertilizer was forecasted based on regional optimal N rate and crop cultivated area in this study. The agricultural nitrogen fertilizer demand is expected to31.33million tonnes in China, and increase Chinese wheat, maize, rice production by8.5%,13.2%,7.4%, respectively.