Comparison Of Soil Organic C In Loess Plateau And Subtropical Hilly Regions Of China

The Loess Plateau region is one of the friable regions in China and there are many factors limiting the accumulation of soil organic carbon (SOC), such as aridity, erosion and vegetation degradation, and so on. The agricultural productivity of subtropical hilly region is superior to the Loess Plateau distinctly. Therefore, study of the SOC contents differences of two regions and its key controlling factors is of great important for the soil fertility regulation and controlling of the farmland in China. Taking Yangou watershed in the Loess Plateau and Pantang area and Kenfu area in subtropical hilly region of China as examples, the contents of SOC and its active components of surface soils (0~20cm) were studied based on the field surveys and the impacts of the key controlling factors, such as land use, landform and vegetation on SOC were discussed in this study. The main results were as follows:1. Mean SOC content was 7.50 g/kg in Yangou watershed in Loess Plateau. Mean SOC content of the woodland was the highest (9.88g/kg), those of the dry land and orchard were the lowest (4.67g/kg and 4.33g/kg), and those of the grassland were in the middle. The coefficients of variation of SOC of the woodland was higher and those of the orchard was lower, belonging to moderate variation. There were significant positive correlations between SOC and total nitrogen (TN) under different land uses in the area. Soil C/N ratio of the woodland were the highest and there were no significant differences among those of the grassland, dry land and orchard. There were significant positive correlations among soil dissolvable organic C (DOC) and microbial biomass C (MBC) and SOC in the area. The study indicated that conversion of farmland into woodland or grassland promoted the accumulation of SOC distinctly and orchard constructions accelerated the decomposition of surface soil organic C in the area. The cross sections of a small valley can visually express the distribution of SOC in three landforms. Mean SOC content of the tableland in Yangou watershed was the lowest, that of bottomland was the highest, and that of slope land was in the middle. Aspect affected significantly the SOC contents of the woodland and grassland, with no significant effects on those of dry land and orchard. The SOC contents under the condition of natural recovery of grasses, bushes and woods were significantly higher than that under man-built vegetation. For the slope dry land, the SOC content was low and similar along the slope. For...