Effects of Soil Erosion on Soil Physicochemical Properties and Soil Microorganisms

Soil erosion is a serious problem in the Loess Plateau. It reduces soil productivity,causes irreversible soil and soil nutrient loss. Although many studies about the effects of soil erosion on soil nutrients,sediments and runoff have been done,the quantificational research on the relationship between soil erosion and soil nutrients,especially with soil microorganisms,was limited. In this study,the137Cs tracer method was used to research the relationship between soil erosion with soil physicochemical properties and soil microorganisms in erosion environment in the hilly area of the Loess Plateau. The experiment was conducted in the Yangjuangou Valley located near Yan'an City in north Shaanxi Province,China. Four typical hill slopes including F( artificial forest),G( grass),G-F-G( grass on upper and lower slopes and artificial forest on middle slope) and F-G-F( artificial forest on upper and lower slopes and grass on middle slope) were chosen. On each of the four slopes,soil sampling sites were distributed on the summit,shoulder,backslope,footslope and toeslope along the hill-slopes. Soil samples were collected in August 2007 for analyzing of the concentration of137Cs which could indicate soil erosion degree,soil physicochemical properties including the soil organic carbon content,total soil nitrogen content,soil bulk density,electrical conductivity,pH value,soil water content and soil microbial properties including soil microbial carbon,soil microbial functional diversity and soil microbial community structure. The results showed that the concentration of137Cs varied significantly between different slope positions,and the distribution of137Cs along hill-slope was different under four vegetation patterns. There was a significant regression relationship among soil organic carbon content,total soil nitrogen content,soil bulk density,electrical conductivity and137Cs concentration. Soil organic carbon content,total soil nitrogen content and bulk density were increased with the increase of137Cs concentration but the decrease of electrical conductivity. There was no significant correlation between the soil water content and pH value and the concentration of137Cs. There was no direct impact of soil erosion on soil microbial biomass and neither the significant relationship between137Cs concentration and soil microbial biomass. However,the regression analysis indicated that soil erosion could affect significantly soil microbial diversity and soil microbial community. Soil microbial functional diversity was decreased,and soil bacterial biomass was decreased at first and then increased with the increase of137Cs concentration. In conclusion,soil erosion could directly impact the distribution of soil nutrients and soil structure on slope.