Estimation of annual CH4 and N2O emissions from solid dairy manure storage in Yanqing of Beijing based on dynamic chamber method

Abstract: Greenhouse gases, such as methane (CH4) and nitrous oxide (N2O) caused by manure storage inside the dairy farms are important contributors of global emissions to atmosphere, which is considered as the primary factor driving global warming. The Intergovernmental Panel on Climate Change (IPCC) guideline (Tier 2 for example) released in 2006 is treated as an authoritative method in estimating CH4 and N2O emissions from the animal manure management of a region, while its accuracy highly depends on the reliabilities of the parameters, including the CH4 and N2O emission factor (EF). While, different manure management modes and climatic conditions will lead to huge difference of the factors, and the estimation based on default factor of IPCC may result in a big deviation in the emissions from the manure management for a country or an area. Using the IPCC method, this paper simulated CH4 and N2O emissions from short-term stacked dairy manures in spring, summer and autumn by the dynamic chamber technique in the laboratory, and the annual emissions of CH4 and N2O from the manure management in Yanqing dairy farms was estimated based on the simulation results, as well as the field investigation on dairy management method and manure production. Finally, CH4 and N2O emission factor of the dairy manure management were calculated and compared with the defaults of IPCC. Results showed that CH4 emissions from the simulated dairy manure stockpiles were 223.97, 4 603.31 and 351.38 mg in spring, summer and autumn, respectively. The total CH4 emission of solid dairy manure management in Yanqing, Beijing was 13 342.50 kg in 2016, or 373.59 t CO2 equivalent. CH4 emission factor of solid manure storage from the simulation was 1.50 kg/(head·yr), which was statistically less than 1.78 kg/(head·yr) calculated from the default values of the relevant parameters in the IPCC guidelines. N2O emission from the simulated dairy manure stockpiles were 5.86, 9.43 and 0.81 mg/kg in spring, summer and autumn, respectively. Total N2O emission of solid dairy manure management in Yanqing, Beijing was 347.87 kg in 2016, or 92.19 t CO2 equivalent. N2O emission factor of solid manure storage from the simulation was 0.0004 kg/kg, which was significantly less than the defaulted value of 0.005 kg/kg in the IPCC guidelines. The difference on the emission factors could be partially explained by the storage period of collected manures from the barns and the open lots of dairy farms in Yanqing, Beijing, which was general less than 4 weeks, and quite differed from the circumstance that the default EFs of CH4 and N2O in IPCC guidelines. Thus, estimating the CH4 and N2O emissions from Yanqing area of Beijing with the default values of CH4 and N2O emission factors in the IPCC guidelines, the flux will be highly overestimated.