The Effect of Cultivation on the Greenhouse Gases Emissions in wujiang river Basin, Yangtze River, China

Climate change has gained extensive international attention due to the impacts on the regional agriculture and water supply. According to IPCC, the global mean temperature will increase by 0.3-0.8 centigrade. Greenhouse gases such as CO₂, CH₄, and N₂O will concentrate and global mean temperature are projected to be increasing. This study separately examines the Greenhouse gases effect arise from different tillage type (dry land and paddy crop) in Wujiang river basin using DeNitrification - DeComposition (DNDC) model. The simulations indicate that, the atmospheric CO₂ and CH₄ concentration increases with the paddy crop plants. Although between two irrigation periods, the field drying event can decrease the CH₄ production effectively. In addition, the paddy soils in this region tend to increase the effect of carbon source resulted from the flooding irrigation. Especially in the first flood irrigation period, the N₂O increases to the maximum value. By contrast, in crop land under rotation of rape and Maize, the effect of carbon sink induced from CO₂ fertilization could generally offset the effect of carbon source. Meanwhile, the effect of carbon sink increased resulted by the plant grows. Thus, the production of CO₂ is always negative. There is no CH₄ production in crop land under rotation of rape and Maize. By contrast, with fertilization input, the N₂O production increases from 0.05 kg C/kg to 0.5kg N/ha/day. The SOC from the top soils (0-10 cm) to bottom (40-50 cm) decreases from 0.021 kg C/kg to 0.014 kg C/kg in either dry land and paddy soils of the Wujiang River region from 1991 to 1994, respectively. These results suggest that SOC storage in paddy and dry land of this region is steady. For the dry land crop (rotation of rape and Maize), the N₂O increased with the fertilization. But for the paddy soils, the irrigation time is the key point period for greenhouse gases production and the variation of carbon and nitrogen in soil. As a representative of paddy crop and dry land crop (rotation of rape and Maize) in western China, the insights gained from the Wujiang River basin may be potentially transferable to other similar agricultural practices in other part of China.