Carbon Sequestration and Gas Emissions in Paddy Field Ecosystem Affected by Nitrogen Application in Purplish Soil, Southwest China
Greenhouse gas emissions (GHGs) from a purplish paddy field (Regosol in the FAO taxonomy) were measured by the static chamber technique in 2005 in Sichuan Province, Southwest China. Four treatments with three replicates each were N0 (0 kg N · ha–1), N150 (150 kg N · ha–1), N75-S (75 kg N and 10620 kg wheat straw · ha–1) and N150-S (150 kg N and 10620 kg wheat straw · ha–1) under the same fertilization of 45 kg P2O5 and 45 kg K2O · ha–1. Carbon sequestrations, gas regulation services and their economic values were evaluated. Results showed: the average flux and seasonal emission of CH4 increased significantly with increasing straw application rates; those of CO2 increased significantly with increasing straw and nitrogen application rates; those of N2O increased with nitrogen application rates, whereas decreased with straw application rates. In the anthesis stage, with the increase of nitrogen application, the photosynthesis C fixation increased. The C emission of N150 was the greatest in all treatments both in the anthesis and milking stages. All plots were carbon sinks (uptake > emission). The overall economic values of N0, N150, N75-S and N150-S were 893.218, 1430.580, 1323.262 and 1677.327 USD∙ha-1 respectively. The overall values were all positive, indicating that these ecosystems actually contribute to environmental sustainability in terms of the production of O2 and reduction of GHGs. The maximum overall economic value of gas regulation was N150-S.