Emission Factors Of N₂O From Farmland In Central China And The Influencing Agents

The global climate change, caused by a large number of greenhouse gas emissions, has affected human survival and development. Agriculture, which is a major source of greenhouse gas emission, is recognized as one of the most important affecting factors of global climate change. Previous information showed that agriculture accounted for 10%-12% of total global anthropogenic emissions of greenhouse gases. Nitrous oxide （N₂O） is an important part of greenhouse gases, and agricultural soil is a major source of N₂O emission. The soil environment, regional climate characteristics and tillage management measures can affect soil microbial activities and subsequently change the emission of N₂O. Quantitative analyzing agricultural N₂O emission factors and establishing the emission models when combine with the regional production characteristics, are beneficial to identify the key affected factors of N₂O emission and reveal the N₂O emission mechanism.In this study, we collected the data of N₂O emission based on the previous studies and established the research database after the screening. A Meta-analysis was conducted to investigate the effects of different climatic conditions, soil properties, and farmland management measures on agricultural N₂O emission in central of China with Response Ratio （RR） in the form of 1nRR. Based on the N₂O emission coefficient method in Intergovernmental Panel on Climate Change （IPCC）, we established an empirical model for farmland to describe the relationship between N₂O emission and N application quantitatively without considering other affecting factors. Moreover, combining with the results of Meta-analysis and the existing research, constructed farmland N₂O emissions model with considering of other affecting factors. At last, the constructed model was applied to determine the emission factors and evaluate agricultural N₂O emission in Hubei Province. The main conclusions are as follow:（1） Under the application of nitrogen fertilizer, the factors such as the methods of fertilization management, soil and climate conditions as well as the tillage management measures have played significant roles in the direct emission of N₂O respectively.（2） Taking into account the relationship between N₂O emissions and influencing factors, N₂O emissions from agricultural fields in central China can be calculated by the following model. E=-7.4796+1.1782C-0.0427C2+0.0227pH2+（0.0760+8.40 × 10-6 CL2-5.23 x 10-4 CL+5.57 × 10-8 P2-1.17 ×10-4P-0.0016TN）×N R2=0.8284, P<0.0001. Compared with the method provided by IPCC, the estimation model introduced of soil, climatic factors, can simulate the process of agricultural N₂O emissions accurately. The percentage of soil clay content, total nitrogen and average annual rainfall would significantly affect N₂O emission factors while the background emission of N₂O was influenced by the content of soil organic carbon and pH. The results of Monte Carlo showed that the N₂O emission models are relatively stable.（3） Estimated the soil N₂O background emissions and N₂O emission factors for each city in Hubei Province based on the constructed model. The values of soil N₂O background emission in Hubei Province were in the range of 0.67 to 1.57 kgN₂O-N/hm2, average value was 1.12 kg N₂O-N/hm2, which is close to IPCC 2006 value of lkg N₂O-N/hm2. It showed that N₂O emission factors were within the scope of 0.67 to 1.57 kgN₂O-N/hm2, with an average of 0.0096 kgN₂O-N/kgN. Which was slightly lower than the recommended value from "The guidelines for Provincial Greenhouse Gas Inventories" （0.0109 kgN₂O-N/kgN）. Furthermore, in 2012, the overall emission of N₂O from agricultural soil caused by nitrogen fertilization in Hubei Province was 22819.53 t which was 3929.22 t less than "The Guidelines for Provincial Greenhouse Gas Inventories".