Distribution Characteristics And Turnover Of Soil Profile Methane,Nitrous Oxide And Carbon Dioxide In Paddy Fields

Global wanning is mainly caused by increasing atmospheric greenhouse gas concentrations. Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) have been recognized as the important greenhouse gases. Soil carbon and nitrogen cycles play a vital role in changing of atmospheric concentrations of greenhouse gases. Since the soil is an complex system, it’s very important to study the soil profile concentrations of greenhouse gases and their turnover rate for further understanding of their production mechanism and behavior process under paddy ecosystems.Our focus in this study is to investigate the dynamic distribution patterns and turnover rates of CH4, N2O and CO2in the paddy soil profiles with different rice-based cropping systems. A special soil gas collection device was adopted to monitor the dynamics of CH4, N2O and CO2at soil depths7cm,15cm,30cm,50cm in the paddy fields under both flooded and drainage conditions. The field experimental was performed in the town of Mo Ling, Nanjing City, Jiangsu Province, China (31"58’N,118°48’E), from November,2009to November,2010, including wheat-single rice and oilseed rape-double rice cropping systems. Four treatments were established for each cropping system including the control (ck), nitrogen fertilizer without straw incorporation (SO), nitrogen fertilizer with low level straw incorporation (S1) and nitrogen fertilizer with high straw incorporation (S2). A fallow plot was also included for comparison.Under different flooded rice-upland crop rotations, higher CH4concentrations and turnover rates mainly occurred within the topsoil of0-15cm during the flooded rice-growing season than the other depths; CH4concentrations and turnover rates were generally low during the growth seasons of winter wheat and oilseed rape. Straw incorporation increased CH4concentrations and net turnover rates within the topsoil during the rice growing season.Under different flooded rice-upland crop rotations, higher N2O concentrations were observed at the lower layers than the upper layers throughout the upland crop growing season:30cm≥50cm≥15cm≥7cm for wheat season and50cm≥30cm≥15cm≥7cm for oilseed rape season. Whereas during the single rice and double rice growth seasons, N2O concentrations were significantly.higher at topsoil of7cm and15cm than those at the lower layers of30cm and50cm. Higher N2O turnover rates occurred in the topsoil of0-15cm during both the upland crop season and rice-growth season. Application of nitrogen fertilizer promoted N2O concentrations and turnover rates.Soil profile CO2concentrations during the summer rice-growing season were significantly higher than those during the winter wheat and oilseed rape growth seasons. The CO2concentrations increased with increase in soil profiles throughout the wheat and oilseed rape growing seasons. In the single rice and early rice growing season, CO2concentrations increased with an increase in soil depth for7cm,15cm and30cm depths; No further increase at the soil depth of50cm. In the late rice growth season, the CO2concentrations at the soil depths of15cm and30cm were higher than those at the soil depths of7cm and50cm. Soil profile net CO2turnover rates were higher during the rice growth season than those during the upland crop growth seasons. The net CO2turnover rates were higher in the topsoil of0～15cm during both wheat-single rice and oilseed rape-double rice growing seasons than other soil layers.