Mineralization Patterns of Maize Straw in Fluvio-Aquatic Soil as Determined by Isotopic Traces

The mineralization of plant residues results in changes in soil C and N. However, it is difficult to determine the origins of C and N from either soil organic matter mineralization or residue decomposition using traditional methods. An incubation experiment containing two treatments (blank soil (BS) and soil with 6% maize straw (MS)) was conducted to assess the contributions of maize straw to gas emissions, and to soil organic carbon (SOC) and total nitrogen (TN) using isotopic tracers. About 11.5% of maize straw C was sequestered in soil, the cumulative amount of C emitted from MS was 2.5-fold higher than that in BS treatment. A positive priming effect of maize straw on native SOC in the first 14 days was observed, and then became negative, indicating the potential for a positive balance of SOC storage. Cumulative N2O emissions in MS markedly decreased by 22.4% compared with BS, and the loss of N via N2O in MS was approximately 3.3%. Maize straw significantly increased soil TN and contributed 15.8% to TN at day 120. Our study clearly demonstrated that the different dynamics of C-13 and N-15 in the soils and gases indicated differences of maize straw C and N during decomposition. Maize straw C preferred to contribute to CO2 emissions, while maize straw N contributed more to soil TN.