Soil Quality Status Of Typical Land Uses In Hilly And Gully Region Of Loess Plateau

In hilly and gully region of the Loess Plateau,two gully land improvement and utilization projects have been implemented,namely,damming mud and silting land and gully reclamation.The comprehensive management policy of returning farmland to forest on the mountain to protect the ecological environment and building land below to ensure food security has improved the regional ecological environment and expanded the cultivated land area.It is very important to accurately evaluate the soil nutrients and quality status of different land uses after gully land improvement to ensure project quality,improve cultivated crop yield and ensure agricultural sustainability.This study takes the soil of woodland,grassland,farmland and dam in hilly and gully region of the Loess Plateau as the research object.Through the combination of field sampling and indoor analysis,the distribution characteristics and change rules of soil physical,chemical and biological indexes of different land use modes are studied.The minimum data set is established by used principal component analysis and correlation analysis combined with Norm value.The weighted sum method index evaluation model was used to calculate the soil quality in the study area,and the obstacle degree model was used to quantitatively analyze the obstacle factors affecting the improvement of soil quality in each utilization mode.The main results were obtained as follows:(1)There was no significant difference in soil particle composition among different land uses,with sand content > silt content > clay content and sand content close to 60%.the soil texture was single in the region.Soil p H values ranged from 7.51 to 8.64,all of which are weakly alkaline.The content of organic matter,ammonium nitrogen,alkali-hydrolyzed nitrogen,available potassium and the activities of sucrase,urease and alkaline phosphatase are the highest in woodland soil,the catalase activity of shrub and grassland are the highest,the water content of grassland is the highest,the available phosphorus content of farmland is the highest,and the electrical conductivity content of newly created land is the highest.There are no significant difference in p H value,nitrate nitrogen content and culturable microorganism quantity among different land uses.(2)Soil nutrients showed obvious surface accumulation effect under all land use modes.With the increase of soil depth,soil organic matter,nitrogen,available potassium content,activities of sucrase,urease,alkaline phosphatase and the number of culturable microorganisms decreasing.Soil p H value showed an increasing trend.The soil water content increasing first and then decreasing.Soil electrical conductivity,available phosphorus content and catalase activity are evenly distributed in the vertical direction.(3)Using principal component analysis and correlation analysis combined with norm value to establish minimum data set,The minimum data set index and its weight for soil quality evaluation in 0-30 cm soil layer are electrical conductivity(0.234),sand content(0.185),catalase(0.171),alkaline phosphatase(0.170)activity and bacteria count(0.240).The minimum data set and weight of soil quality evaluation in 30-60 cm soil layer are sand content(0.146),electrical conductivity(0.207),organic matter content(0.222),available phosphorus content(0.208)and actinomyces quantity(0.216).The minimum data set and weight for soil quality evaluation in 60-100 cm soil layer are sand particle size(0.206),electrical conductivity(0.309),catalase activity(0.255)and actinomyces quantity(0.230).The soil quality index based on the minimum data set and the total data set showing a significant positive correlation.The minimum data set could replace the total data set and accurately reflect the soil quality in the study area.(4)The soil quality index of the study area is forest land(0.475)> dam land(0.364)and grassland(0.377)> newly constructed land(0.308),0-30 cm soil layer(0.401)>30-60 cm soil layer(0.346).The diagnostic model of obstacle factors showing that the obstacle factors of soil quality in woodland were sand content(21.33%)and bacteria quantity(39.29%),and the obstacle factors of farmland were alkaline phosphatase activity(30.21%)and bacteria quantity(39.58%),both of which are severe obstacles.Applying bacterial fertilizer and improving soil enzyme activity are effective measures to improve soil quality in the study area.The soil quality in the study area at a medium or low level,and the difference of soil quality are obvious among different land uses,among which the arbor forest land had the highest soil quality.The quality of surface soil is significantly better than that of deep soil.The obstacle factors affecting soil quality improvement in different land use modes are different.A large amount of land is created in a short period of time,but the soil quality of the newly created land is poor due to heavy machinery crushing and poor topsoil covering.New land should increase the input of organic matter and bacterial fertilizer,improve soil enzyme activity,so as to improve soil quality and ensure the sustainable use of cultivated land.