Modelling the dynamics of soil organic carbon mineralization on water-eroded sloping land in the Loess Hilly Region
ZhangYafeng, XuMingxiang, ChenGai, WangChaohua
(1. State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau,Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water resources, 712100, Yangling, Shaanxi, China; 2. University of Chinese Academy of Science,100049, Beijing,China; 3. Forestry College, Northwest A & F University,712100,Yangling,Shaanxi,China
[Background] In order to understand the mechanism of soil carbon emission under soil erosion, we chose the study area located in Ansai County of Shaanxi Province. It is a typical loess hilly and gully region where annual precipitation distribution is not even, precipitation on July-September accounts for about 60% of annual rainfall, and most are heavy rainstorms. The zonal soil is dark loessial one that lost completely due to serious soil erosion, thus soil is mainly loessial one (calcareous ustic cambisols) developed from parent-soil loess. As one of the most serious water erosion area all over the world, the selected area is suitable for exploring erosion induced carbon emission. [Methods] Based on the orthogonal experiment design with three factors (soil organic carbon (SOC) level, soil temperature, and water content) and four levels of the factors, incubation experiment for soil mineralization was conducted with soil sampled at different slope positions of a water-eroded sloping land under different soil organic carbon background in the Loess Hilly Region. Random sampling method was used to collect samples in the positions of water-eroded sloping land (control area, eroded area and deposition area). The dynamic characteristics of SOC mineralization were analyzed and modelled. [Results] 1) SOC level, soil temperature and soil water content affected significantly the mineralization rate and accumulated mineralization amount of SOC (P <0.05). The primary and secondary relation of the three variables was: SOC level > soil temperature > soil water content. 2) Based on the first-order kinetic equation, which could well describe the accumulation dynamics of soil organic carbon mineralization, a multi-factor equation with high fitting degree was obtained by modifying the Cp value (R2 > 0.95). [Conclusions] 1) Soil organic carbon content was one of the main factors affecting the soil organic carbon mineralization at different slope positions. The response of soil organic carbon mineralization to soil erosion on the eroded slope varied with the soil organic carbon background of the sloping land. The mineralization of soil organic carbon was stimulated at sediment area of the slope with a lower content of soil organic carbon, whereas it was depressed with higher organic carbon content. 2) The first-order kinetic equation well described the accumulation dynamics of soil organic carbon mineralization (r > 0.98), its Cp value (organic carbon mineralization potential) reflected the influence of soil organic carbon, soil temperature, and water content on organic carbon mineralization. 3) Through modifying the Cp value, a multi-factor equation for describing the dynamics of soil organic carbon mineralization was obtained. This equation presented a solid fitting effect on predicting the dynamics of soil organic carbon mineralization under different soil organic carbon levels.