Estimating Spatio Seasonal Dynamics Of Methane Emissions From Cattle And The Influence Factors In China

The greenhouse gases emissions due to human activities are considered the major cause of global warming. Methane is the second most important trace greenhouse gas in the atmosphere and contributes about18%of the total global warming whereas CO2has a contribution of50%. The global warming potential of CH4is25times over CO2at the100years horizon. Methane is also the active participant in the process of atmospheric chemistry. The average lifetime of methane in the atmosphere is12years, which is long enough to allow CH4transporting globally. The principal anthropogenic methane sources are:energy consumption, rice, livestock, and landfills. The ruminants are responsible for37%of anthropogenic methane emissions. China has a huge livestock population, the livestock methane emission was estimated to account for50%of the total agricultural methane sources. Cattle accounts for80%of the large livestock populatioin.A lot of previous studies had made direct measurements of the emission factors and estimated the methane emissions from livestock with the measured emission fators. Up to now, the spatial distribution and temporal variation of CH4emissions from livestock was made by considering only the spatiotemporal variation of the livestock population. Because of the varying body properties among different cattle species and their spatial distribution of the cattle species, the emission factors vary spatially. And besides the body features, the estimate factors may also change with other factors such as the quantity and quality of feed, age and environmental conditions. The objective of the present study was to explore the differences between individual species of cattles and the spatial distribution and temporal variation of CH4emission factors of cattles in China.The methane emissions from livestock have two parts:from enteric fermentation and manure management systems. The IPCC proposed methods to estimate CH4emissions from each species of cattles, including draft cattle, buffalo, yak, dairy cattle and beef cattle. With the data of individual body weight, milk production and feed digestibility etc., we calculated the species-specific emission factors for different cattle species via the Tier2method of IPCC. To caculte the total emission, the census data of the livestock population was collected from China Agriculture Yearbooks and re-allocated to a1km*1km grid by referencing to the land cover/use datasets.In the data of cattle properties collected in the present study, the lagest bull weight is764kg in North-East District, and the minimum is215kg in The Tibetan area. The Xinlin buffalo can produce averagely7kg milk per day, but some species like Dechang buffalo produces only1.4kg milk per day.The enteric emission factors (the monthly methane emission) of draft cattle, buffalo, yak, dairy cattle, and beef cattle are5.44,6.30,5.50,2.77and8.11kg/head/month respectively, and the manure emission factors are0.268,0.242,0.254,0.133and0.642kg/head/month respectively. The seasonal changes of the enteric emission factors of the five cattle categories are all "V" shaped, low in summer and high in winter due mainly to the seasonal changes of the diets. But the manure emission factors showed a seasonal variation in contrary to the enteric emission factors, high in summer and low in winter, owing to the seasonal changes of temperatures. The high manure emission factors of dairy cattle and buffalo is1.186and0.431kg/head/month in July;0.455and0.233kg/head/month from draft and beef cattle in June, and0.441kg/head/month from yak in May.The monthly enteric emission factors of draft cattle, dairy cattle and beef cattle in pasture are5.74,9.45and3.80kg/head/month, larger than in the rural area. The manure emission factors of draft cattle, dairy cattle and beef cattle in pasture is0.097,0.325and0.055kg/head/month, smaller than in the rural area that is0.297,0.695and 0.146kg/head/month, respectively.The total emission of all cattle, buffalo and yak in China is11.5Tg, and the emission from draft cattle, buffalo, yak, dairy cattle and beef cattle is5.9,2.1,1.1,1.7and0.7Tg, respectively.