Characteristics Of Soil Aggregation,Carbon And Nitrogen Differentiation In Sandy Grassland In Eastern Ningxia Wind-sand Area

To explore the differentiation characteristics of soil structure,organic carbon and nitrogen during the sandy desertification process of grassland Ningxia eastern sand-wind area,the potential desertification grassland,the light desertification grassland,the moderate desertification grassland and the severe desertification grassland were selected as the research objects.The soil aggregate stability,profile distribution of organic carbon,total nitrogen and its components and carbon and nitrogen mineralization characteristics at 0-40 cm soil layer were studied.The main results were as follows:(1)The soil mechanical stability and water stable aggregates at the 0-40 cm soil layer of various types of desertification grassland generally had the dominant particle size of the micro-aggregates<0.25 mm,and the Percentage of aggregate destruction were high.With the intensification of desertification,the DR0.25,WR0.25,MWD and GMD gradually decreased,while the fractal dimension and K-factor of soil erosion were increased,and the aggregate structure tended to be unstable.(2)The soil organic carbon and total nitrogen contents at the 0-40 cm soil layer decreased were 2.87 g/kg-17.29 g/kg and 0.067 g/kg-0.487 g/kg,and the carbon and nitrogen reserves were 4.60 t/hm2-22.66 t/hm2 and 0.11 t/hm2-0.64 t/hm2 respectively.They all decreased with the aggravation of desertification,and those in the potential desertification grassland were significantly higher than those in the light,moderately and severely desertification grassland.The contents of organic carbon and total nitrogen in the aggregates of different particle sizes decreased with the aggravation of desertification,and the contribution rate of>5 mm and<0.25 mm particle sizes to organic carbon and total nitrogen in the whole soil were higher.(3)The contents of easily oxidized organic carbon,nitrate nitrogen and ammonium nitrogen at 0-40 cm soil layer did not change significantly with the aggravation of desertification.The contents of microbial biomass carbon and nitrogen at 0-30 cm soil layer decreased with the aggravation of desertification.Except soil microbial biomass carbon,the proportion of other carbon and nitrogen components in total organic carbon or total nitrogen increased with the increasing degree of desertification.(4)The mineralization rates of soil organic carbon at 0-40 cm soil layer in grassland of different desertification types showed similar variation trend with the extension of culture time.The mineralization rate of organic carbon was high in the early stage of culture,and then decreased rapidly and became stable.Therefore,the mineralization of soil organic carbon was divided into rapid release stage(1-7 d)and slow release stage(9-56 d).There was no significant difference in soil organic carbon accumulation and mineralization between different desertification types.The mineralization rate of soil organic carbon accumulation and C0/SOC increased with the aggravation of desertification.(5)During the 56 days culture period,the process of nitrogen nitrification and ammoniation at the 0-40 cm soil layer in grassland of different desertification types can be roughly divided into two stages.The mineralization rate of 1-21d showed decreasing-increasing-decreasing trends,and the amplitude is large,and tends to be stable from 21d to56d.The nitrogen mineralization was dominated by nitrification.The nitrogen mineralization amounts and nitrogen mineralization rates of the soil generally declined with the aggravation of grassland desertification.(6)The stability of soil aggregates was positively correlated with soil organic carbon,total nitrogen,microbial biomass carbon,ammonium nitrogen and nitrogen mineralization,and negatively correlated with easily oxidized organic carbon and carbon mineralization.In the process of grassland desertification,iaccompanied by the blow of the soil erosion,soil structure tend to be unstable,the soil carbon and nitrogen loss.In the conversion process of different types of desertification grassland,the soil aggregate composition and carbon and nitrogen contents changed significantly from the potential desertification grassland to the light desertification grassland,so the potential desertification grassland is the key stage for ecological environment protection and desertification prevention and control in Ningxia sand-wind area.