Greenhouse Gases Emissioms From Agriculture Residues Burning

The increasing concentration of greenhouse gases in the atmosphere, such as CO2, CH4and N2O has been paid much more attention due to their substantial contribution to global warming. The annual amounts of agricultural residues in China were tremendous. And it is not in such high demand as fuel, agricultural residues increasingly are being burned in the field. Crop residues burning have been considered an important source of atmospheric species and to have a significant impact on global atmospheric chemistry. So it was necessary to study greenhouse gases (CO2, CH4and N2O) emissions from agricultural residues combustion and returning to fields after combustion.In order to find out the spatial-temporal variation of the proportion of6agricultural residues (rice, wheat, maize, oil rape, cotton and soybean) used as household fuel, direct open burning and its influencing factors in different periods (1990-1995,1996-2000,2001-2005and2006-2008), the questionnaire survey during the above4study periods in47counties of Jiangsu province was carried out. The emission inventory of greenhouse gases from agricultural residues burning was established according to the burning percentages and emission factors, ratios of dry residues to production and crop productions of different periods in Jiangsu province. Emission factors CO2, CO, CH4and N2O of the6agricultural residues were calculated by the simulated burning experiment. Respiration, CH4and N2O emissions were measured from different treatments in indoor incubation and apot-experiments, and finally the global warming potential (GWP) of greenhouse gases emission from the wheat straw combustion (including direct combustion and returning after combustion) and the incorporating straw treatment were compared.Questionnaire results showed that the mean proportion of agricultural residues used as household fuel during the4study periods were62.81%,59.76%,27.55%and24.13%, respectively, and the mean proportion of agricultural residues open burning in fields were21.16%,23.93%,53.29%and47.87%, respectively. They had an opposite trend and the obvious change appeared in second and third research periods. There was regional disparity for agricultural residues utilization in north (including Huaian, Suqian, Lianyungang, Xuzhou and Yancheng), middle and south region (including Nantong, Yangzhou, Taizhou, Zhenjiang, Wuxi and Suzhou) of Jiangsu province. The proportion of crop agricultural residues used as household fuel (54.22%) in north region was higher than the middle and south region (34.68%), while the ratio of agricultural residues open burning (29.60%) was lower than the middle and south region (42.37%). The proportion of agricultural residues open burning had significant linear positive relationships (P<0.01) with the ratio of farmers taking job in cities, age of farmers, family income and kitchen power consumption. Logistic regression model established declared that4factors had a significant effect on the farmers’willing to chose agricultural residues open burning in fields, and the influence degree followed the order of the ratio of farmers taking job in cities> acreage> family incomes> the ratio of agricultural residues used as household fuel.Emission factors of CO2, CO, CH4and N2O depended on crop straw types. The emission factors of CO2and CH4were higher for canola straw than the other straws, while the maize and the rice straw had the higher N2O and CO emission factor. Emission inventory of greenhouse gases from agricultural residues burning in Jiangsu province indicated the annual average global warming potential (GWP) of6tested crop straws were estimated to be9.18(rice straw),4.35(wheat straw),2.55(maize straw),1.63(canola straw),0.55(cotton straw) and0.39(soybean straw) Tg CO2equivalent, respectively. It could be seen the emissions from wheat and rice straws combustion had the maximum contribution to the GWP. Among the4study periods, the annual average GWP had no significant difference between the1990-1995and2006-2008periods, while the maximal annual average GWP (23.83Tg CO2equivalent) happened in the2001-2005periods, and the minimum (20.30Tg CO2equivalent) in1996-2000periods.The indoor experiments results indicated that, compared with the straw incorporated after combustion, directly applying the rice and wheat straws to soil significantly enhanced soil respiration and N2O emission under draught condition, and markedly increased CH4emission under flooding condition.The experiment of the rice growing season results indicated that the mean CH4emissios from the wheat straw incorporated were about1.2times higher than the straw incorporated after burning, but there was no significant difference between them (P>0.05). The experiment of the soybean growing season results revealed that, compared with the wheat straw directly incorporated, the straw incorporated after burning slightly enhanced N2O emission (P<0.05), and the emissions is about1.3times of the former.Hypothesized that wheat straws were all incorporated and soybean were planted in the all fields during2006-2008persiods, GWP of greenhouse gases emissions from the wheat straw combustion (including directly combustion and returning to soil after combustion) and directly incorporating wheat straw calculated showed that the GWP of the former was larger than the latter.In the context of mitigation, incorporating straw is comparatively the preferable measures.