Effects Of Enclosure Management On Soil Organic Carbon And Aggregate Stability Of Desert-steppe In Ningxia

Enclosure is one of the most convenient and efficient measure for restoration of degraded grassland ecosystems. In this study, we selected the desert steppes which were enclosed against grazing in different years and studied the stability of soil aggregate, the concentration and distribution in different soil depth and different soil aggregate of soil organic carbon and its components. The main results were as follows:Based on changes of R0.25, MWD, GMD, in preliminary stage of enclosure, vegetation restoration succession was beneficial to the formation of large aggregates. Aggregates composition of the grassland which had been fenced for3years was the best. The structure got worse when the grassland had been fenced for5years. After that, it followed by a slight recovery over time. The influences of fencing on water stable aggregates MWD and GMD were mainly at0-5cm depth. Soil water stable aggregates were better after3years enclosure. With the extended of fencing time after5years, soil water stable aggregates stabilized gradually. With increasing soil depth, The soil aggregate stability increased with soil depth.The organic carbon contents at5-10cm,10-20cm,20-40cm depth were significantly influenced by enclosure. The organic carbon contents at different depth were higher in7-year and10-year fenced grasslands, while those in3-year and5-year fenced grasslands were lower. The particulate organic carbon, soluble organic carbon and readily oxidized organic were highest in7-year fenced grassland.The organic carbon contents of different size aggregates at different soil depth had different responses to enclosure. The organic carbon contents of various size aggregates at0-5cm and5-10cm depth were the highest in3-year fenced grassland, and those at0-20cm and20-40cm depth were highest in7-year and10-year fenced grasslands. Among different particle aggregates,1-0.5mm and0.5-0.25mm size aggregates contribute the most to organic carbon.The soil water contents at10-20cm and20-40cm depth firstly decreased and then increased with fencing. Enclosure had significant effects on soil bulk densities at5-10cm and20-40cm depth. Response of soil nitrogen fencing is mainly reflected in the following10cm of soil. The total nitrogen contents were the lowest in3-year fenced grassland, while they were higher in7-year and10-year fenced grassland.The total organic carbon contents were positively correlated with MWD, GMD, soil prosity and total nitrogen, and negatively correlated with soil bulk density. The soil particulate organic carbon contents were negatively correlated with R0.25, MWD, GMD of dry sieve aggregates and soil water contents, and positively correlated with soil bulk density. Soluble organic carbon contents were negatively correlated with soil bulk density.