Simulating the effects of long-term discontinuous and continuous fertilization with straw return on crop yields and soil organic carbon dynamics using the DNDC model

Abstract

The objectives of this study were to investigate the applicability of the DNDC model under long-term discontinuous fertilization (three years of fertilization followed by three years of no fertilization) in the winter wheat-summer maize rotation cropping system, and to analyze the effects of long-term fertilization and straw return on soil organic carbon (SOC) and crop yields and to optimize the ratio of straw incorporation to fertilization rate. A 30-year (1981–2011) long-term experiment was conducted at the Hengshui ExperimentalStation in Hebei Province with combinations of four inorganic fertilization rates and four maize straw incorporation amounts. Crop yields and SOC contents in the topsoil (0–20cm) were measured for each treatment, and the data were used to calibrate and validate the DNDC model. Resultsindicated the good performance of DNDC model in simulating crop yields and SOC contents with modeling efficiency ≥0.55, normalized root mean square error ≤31.3%, and index of agreement ≥0.85. However, the model performed relatively poorly in four treatments without fertilizers. Determination coefficients between simulated and measured values of the winter wheat yields, summer maize yields, and SOC contents were 0.747, 0.671, and 0.425, respectively. Crop yield and SOC content predictions were better during periods with fertilization than that during periods without fertilization. The rate of increase in crop yields induced by increasing fertilization rates was higher than that induced by increasing amounts of incorporated straw. However, rate of increase in SOC content resulting from increasing fertilization rate was lower than that from increasing amount of incorporated straw. Over 52 scenarios combining 13 levels of fertilizer rates with four levels of maize straw incorporation were simulated. Resultsfrom yields, soil fertility, and greenhouse gas emission showed that the optimal ratio for discontinuous fertilization was 420kgNha−1yr−1 combined with straw incorporation of 10000kgha−1yr−1, whereas that for continuous fertilization was 300kgNha−1yr−1 combined with straw incorporation of 10000kgha−1yr−1. Thus, the DNDC model could effectively predict crop yields and SOC dynamics under discontinuous fertilization conditions in Hengshui. High and stable crop yields and enhanced soil fertility could be achieved by optimizing the ratio of fertilization rate to amount of incorporated straw.