Effects Of Crop Residues Returning On Greenhouse Gas Emissions From Brown Red Soil

Crop residues returning is an important method to improve the soil quality and increase the soil organic matter and then promote the soil ability of carbon sequestration. It will stimulate the microbial activity when the residues are returned into soil and release organic matters and other nutrients, which can affect the carbon and nitrogen cycles and the greenhouse gas (CO2, CH4, N2O) emissions. When conducting crop residues returning, the quality of crop residues, the type and level of applied nitrogen fertilizer, the water conditions, the soil types, etc. are important factors. In this study, we collected the upland soil and paddy soil (brown red soil) from E’nan area to investigate the impacts of different crop residues corporated with different levels of nitrogen fertilizer on the greenhouse gas emissions from upland soil, as well as the impacts of rice straw returning under different water conditions on the greenhouse gas emissions from paddy soil. The main research conclusions are as follows:(1) Crop residues returning promoted the CO2emissions from upland soil and the amout of emission was positively correlated with the amount of residue-C. N fertilizer didn’t increase the CO2emissions further when the rape cake (RC), maize straw (MS) and rice straw (RS) were returned into soil, while it significantly enhanced the CO2emissions when wheat straw (WS) owith high C/N ration was returned.(2) Upland could absorb CH4though the amount is very little, and the application of crop residues and fertilizer didn’t change the CH4absorption by soil.(3) The returning of RC with lowest C/N ratio obviously increase the the N2O emission from upland soil and the increasing degree was futhured by the corporation of N fertilizer. However, the application of N fertilizer had no effects on the N2O emission when the returned residues were RS and MS, whose C/N ratio was relatively higher compared with RC.(4) The application of residues of much low C/N ratio corporated with N fertilizer could result large amount of greenhouse gases (CO2+N2O) emission, and it was much difficult for residues of high C/N ratio to decompose. It was sugggested choosing residues whose C/N ratio was about40because its decomposition can be promoted by the addition of N fertilizer and then improves the soil quality, and will not result relatively large amout of greenhouse gases emissions at the same time.(5) After the application of N fertilizer, the rice straw returning (SNF) resulted much CO2and little N2O emission from paddy soil, while the flooding condition (NSF) resulted much N2O emission. The N2O production was prohibited and it was even absorbed slightly by soil when these two measures were conducted together (SF). However, the the continiuos mineralization of straw was enhance and thus released much large amout of CO2and CH4.(6) After the application of N fertilizer, the increased releasing of greenhouse gases under SNF and NSF conditions induced the increasing of global warming potential (GWP). The values of GWP were6684.84mg CO2-eqv·kg-1with over99%from CO2and5978.37mg CO2-eqv·kg-1with over50%from N2O, respectively. The GWP was increased to19823.30mg CO2-eqv·kg-1under straw application&flooding contion (SF) with over20%from CH4, which was some3folds of the GWP under SNF and NSF. It was sugggested returning the rice straw after the rice harvesting and soil draining to make it decompose under aerobiotic environment and then conducting the next flooding and rice planting, in order to balance the straw effective ulitilization with its contribution to GWP.