Soil Organic Carbon Simulation Under Different Management Practices In Upland Soils Of Northeast China

Global climate is undergoing significant change with warming as the main feature in the past century. The increasing of greenhouse gas concentration in the atmosphere is one of the main causes of global warming. The effects of different agricultural management practices on soil organic carbon in Northeast China were studied in order to provide a scientific basis for sustainable development and low carbon agriculture aiming at high yield, high nutrient efficient and low pollution in Northeast area. Different agricultural management practices can affect the future changes of soil organic carbon (SOC). This study calibrated the DAYCENT model by using observed crop yield and SOC standards, which based on the collected data of four long-term experiment sites in Northeast China (Harbin Heilongjiang, Gongzhuling Jilin, Dehui Jilin, Shenyang Liaoning). DAYCENT model parameters need to be adjusted, which include crop parameters, tillage parameters, fertilization parameters, harvest parameters, organic fertilizer parameters and so on, and then this study validated the model by using adjusted parameters after calibrating. The simulated and measured values were fitted well, which indicated that the DAYCENT model is applicable to simulation of crop yields and SOC of these four sites and can simulate the dynamic changes of SOC well. While parameters that affect the simulation ability should be analyzed sensitively. The calibrated and validated model was used to simulate the future changes of SOC under four different management practices (fertilizer application, organic manure augment, straw incorporation, and no-tillage) at the future climate change scenario (RCP 4.5). Conclusions are listed as follows:(1) DAYCENT model can simulate the dynamic changes of crop yield and soil organic carbon effectively, which has a strong adaptation, while DAYCENT model can be used to simulate the dynamic changes of the SOC at sites in the future.(2) The fraction of soil carbon pool partitions on the effect of soil organic carbon content is passive pool> slow pool> active pool. Increasing the proportion of passive carbon pool can significantly enhance the content of soil organic carbon. The gap of changes in slow pool fraction and active pool fraction on the SOC contents is small. Increasing the proportion of active pool would reduce the content of soil organic matter. Compared with temperature, moisture and nutrients, the fraction of soil carbon pools does not play a significant role on crop yield.(3) Soil texture significantly affects the simulation results of soil organic matter and crop yield. The importance of clay, silt and sand on increasing soil organic matter content is at the order of sand>clay>silt. Clay and silt both show positive effect on soil organic matter content, while sand content shows negative influence on soil organic matter content. The influence of clay content on SOM is similar to sand. Because soil texture can affect the aeration, water content and soil bulk density, thus these factors affect crop yield significantly.(4) Crop production potential parameter is read in the monthly step in the model which has a very obvious influence on crops yield and therefore it is a sensitive parameter to crops yield.(5) SOC will be increased rapidly in a short period of time by using combined application of organic manure and chemical fertilizer (MNPK) at Harbin site. Although the increasing slope of SOC for lower rate of manure combined with chemical fertilizers and chemical fertilizer showed a consistency in a long period of time, but the absolute value of future SOC content will be higher for MNPK compared to NPK due to its higher initial SOC content.(6) The SOC of no-tillage treatment showed lower than conventional tillage in a short period of time at Dehui site, but no-till seemed to be more effective in increasing SOC in a long period of time though with relatively slow increasing speed, which relatively increased SOC by 11.88% in future 40 years.(7) Combined application of manure with chemical fertilizers and straw incorporation can improve SOC significantly at Gongzhuling site.(8) Due to a slight decreasing trend at Shenyang site, SOC will be decreased by 2.83% in the next 42 years if fertilizers are applied only, so the authors suggested that combined application of organic manure and chemical fertilizers and other carbon addition practices must be adopted.(9)The goal of sequestration carbon can be achieved by using combined rational rate of manure with chemical fertilizers, adopting no-tillage and straw incorporation technologies in Northeast China.