The Effects Of Land Use On Soil Carbon And Nitrogen Storage And Soil Quality In Loess Hilly Region

Different land use patterns have an important impact on soil quality,soil carbon sequestration and nitrogen fixation capacity.In this paper,we selected different soils under seven land use types,in Chengguan Town of Helingeer County,which are natural grassland,sloping land of corn,sloping land of beans,fallow land,abandoned land,returning farmland to shrubs for 3 years and returning farmland to shrubs for 5 years in September 2016.Based on the soil experiments,the soil nutrient contents,soil carbon and nitrogen contents were analyzed.And the soil quality was evaluated by using soil comprehensive quality index and soil degradation index of soil fertility index.The main results are as follows.(1)Soil properties under different land use patternsNatural grassland has the highest contents of soil organic carbon,soil labile organic carbon,total nitrogen,available nitrogen,total phosphorus and available potassium in the soil surface(0-20cm).The difference is that after the contents of soil organic carbon,soil labile organic carbon,available nitrogen and available potassium in farmland five-year shrubs are between the two sloping fields.And Three-year shrubs are less than the former.The contents of total phosphorus and total potassium in sloping farmland were higher than those in returning cultivated shrub land.The fallow land has the least nutrient content.The content of total potassium and total available phosphorus in sloping farmland was the highest,and in returning farmland to shrubs and grasslands were the least.(2)Soil Carbon and Nitrogen Contents and Correlations of Topsoil under Different Land Use PatternsUnder different land use patterns,the contents of soil organic carbon,total nitrogen and soil labile organic carbon generally showed 0-5cm> 5-10cm> 10-20 cm.Under the 0-20 cm soil layer,the soil organic carbon showed a significant correlation between the soil layers.The soil total nitrogen content was higher at 0-10 cm,and the soil easily oxidized organic carbon content was higher at 0-5cm.The order of increasing soil carbon to nitrogen ratio is sloping farmland <shrub woodland <grassland.The ratio of oxidizable organic carbon to organic carbon in soils at different soil depths gradually decreased with the deepening of soil depth,and the change range of soil oxidizable organic carbon was greater than that of soil organic carbon.(3)Soil carbon and nitrogen reserves in soil(0-20cm)under different land use patternsNatural grassland has the highest soil organic carbon and nitrogen reserves.And bandoned land has good recovery capability of soil carbon and nitrogen.In the short term,the soil carbon and nitrogen reserves of cultivated land are lower than that of sloping farmland,and the soil carbon and nitrogen reserves increase with time.In addition,planting black beans is more conducive to soil carbon sequestration and nitrogen fixation than corn planting.(4)The soil quality under different land use patternsSoil quality of abandoned and natural grassland is better than that of sloping farmland,and the soil quality at the initial stage of returning farmland to shrub land was degraded and gradually improved over time.Overall,grassland soil carbon and nitrogen accumulation rate is higher than the other two land use methods.And the rate of carbon and nitrogen accumulation has increased in the conversion of cultivated land into abandoned land,shrub land,and annual growth of bush land.