Effect of Rice Residues on Carbon Dioxide and Nitrous Oxide Emissions from a Paddy Soil of Subtropical China

A pot incubation experiment with rice residues (straw and root) was conducted under aerobic condition (60% of WHC, water holding capacity) for a period of 55 days in a greenhouse. The emissions of carbon dioxide (CO2) and nitrous oxide (N2O) were determined by the closed chamber method in a paddy soil. The soil was derived from quaternary red clay, and collected from the Ecological Station of Red Soil, the Chinese Academy of Sciences, located in Jiangxi Province, a subtropical region of China. The emissions of CO2 and N2O were increased by the amendment of rice residues. Significantly positive correlation was found between N2O and CO2 fluxes (R = 0.650*−0.870*, P ≤ 0.05). The cumulative emissions during the early stage of the incubation (<25 days after residue addition) accounted for about 67%–86% and 67%–80% of the total amount of CO2 and N2O emissions, respectively. Cumulative emissions and emission factors of the two gases were higher in the soils amended with rice straw than those with rice root. The two gas fluxes were positively correlated with microbial biomass C and N, as well as soluble organic C. N2O flux was positively correlated with NH4+–N content at the early stage (<25 days), and negatively with NO3−–N content at the later stage of this incubation (25–55 days), implying that both nitrification and denitrification may have contributed to N2O production.