Case Study On Estimation Of N₂O Emissions From Cropland And Its Carbon Trade At County Scale

N₂O was an important greenhouse gas(GHG)and its mitigation was the main part of agricultural GHG mitigation. Agricultural carbon trade was an effective way for promoting agriculture GHG mitigation. Based on analyzing the nitrogen fertilizer application rate in upland and the potential for reducing emissions in North of China, this paper, taking Huantai county, Zibo city, Shandong Province as an example, applied IPCC method and DNDC model to estimate N₂O emissions from cropland at county scale, and then established a methodology of N₂O mitigation carbon trade from soil testing and fertilizer recommendation project. At last, the farmer's willingness of fertilizer reduction was investigated based on the Logist model. The main conclusions were as follows:(1) Nitrogen fertilizer was the main source of N₂O from cropland,and the N₂O emission factor of the fertilizer application rate was between 0.1 and 2 percent. Taking the huang-huai-hai region for example, from 1990 to 2008, the rate of nitrogen fertilizer application annually increased 3.12%. The nitrogen fertilizer application rate of unit sown area reached 217.4kg N/ha, 3.3 times of the world average. But the use efficiency of nitrogen fertilizer was very low with only 30%-35%. Reduction of nitrogen fertilizer, application of slow-released fertilizer and nitrification inhibitor could effectively reduce the N₂O emissions, the mitigation potential reached 6%～30%,10%～40% and 50%～80%, respectively. It could reduce N₂O emission and increase the farmers' income by carrying out the soil testing and fertilizer recommendation project which was economically and technologically feasible nowadays. But there were still some technological and cost obstacles in application of slow-released fertilizer and nitrification inhibitor and need more experimental and technological improvements.(2) IPCC methodology and DNDC process model were two important methods to estimate the N₂O emission from cropland. The former calculated the N₂O emissions by nitrogen input and emission factor, and the latter simulated nitrification and denitrification process in soil. Comparison with the two methods, the DNDC model reflected the spatial differences more accurately. Until now, there was no CDM methodology for N₂O emission mitigation, and hence this paper established the CDM methodology for N₂O mitigation based on the basic framework of CDM methodology. The boundary of the project included the scope of cropland applied the soil testing and formulated fertilization, and the production process of fertilizer from facility. The baseline of the project included N₂O emissions from cropland under the conventional fertilizer conditions and the CO2 emissions from production of applied fertilizers. The emission of project included the N₂O emission from the cropland under soil testing and formulated fertilization and CO2 emissions from production of applied fertilizer. In addition, the paper also defined the leak and formulated the monitoring plan.(3) Take 11 rural towns of Huantai courty as the basic unit, the N₂O emissions from cropland were estimated by using both IPCC method and DNDC model. The gross and per unit sown area emissions from cropland in Huantai County were 76.02t and 3.01kg/hm2, respectively, with 27.5% higher than the results estimated by DNDC model. Simulation results by DNDC showed that corn-wheat system was the main N₂O emissions source which accounted for 85% of total emissions, and 9.28% for vegetables, 5% for other crops. The results from DNDC model were more reasonable because it comprehensively considered the soil and climate factors.(4) Based on CDM methodologies of N₂O mitigation from cropland at county scale, project document design (PDD) on N₂O mitigation from cropland of Huantai County was carried out. The results showed that by implementing soil testing and fertilizer formulas, the greenhouse gas mitigation reached 26.5 thousand ton CO2 equivalent, amount of which the mitigation from cropland accounted for 25.3% with 9.35 thousand ton, and the mitigation from the nitrogen and phosphate fertilizer saving accounted for 58.3% and 6.8 %, respectively, with 1.54 t and 0.18t CO2 equivalent. The mitigations for each town were different due to the differences of fertilizer rates and cropland area.(5) The fertilizer application rate and the farmers'willingness of decreasing fertilizer were investigated in 7 towns, 190 households from Huantai county by using the stratified sampling method. The results showed that among the surveyed households, only 20.8% of the farmers were willing to reduce the fertilizer application rate, 76.6% of the farmers determined the fertilizer application rate by convention or seller's recommendation, and 70.9% were ignorant about environmental pollution caused by excessive fertilization, which showed that farmers were lack of appropriate technical guidance. The influencing factors were analyzed using Logist model. The results showed that education degree,total area of cropland, cognition of excessive fertilizer, gross income and the proportion of income from cropland all greatly impacted the willingness of decreasing fertilizer rate. Scenario analysis showed that technology promotion, experimental demonstration, government subsidies and regulations, and so on, were all effective ways to promote farmers reducing fertilizer application rate.