Change Characteristics Of Soil Fertility Of Dam Land And Terrace In Loess Hilly Region

Dam land and terrace,as the basic farmland in Loess Hilly Region,take two responsibilities of grain production and soil and water conservation.To study the soil nutrient status plays an extremely important role in the rational utilization of land resources and the improvement of ecological environment.This paper studies the vertical and horizontal distribution characteristics of soil physicochemical and nutrients properties of the dam land and terrace in Yan'an Nianzhuang gully watershed,mainly focuses on the evolution trend of soil nutrients and the characteristics of soil nutrient change in the 2006-2016,and finally discusses the mechanism of soil fertility change through correlation analysis.The following conclusions are as follows:?1?In the 0-20 cm layer of dam land,soil water-stable aggregate content was the highest,the MWD was the largest,the water content was the lowest,the bulk weight was the smallest,and the total porosity was the largest.The dwastribution characterwastics of the MWD,bulk density and total porosity profile of terrace were as the same as dam land.The soil CEC content of dam land and terrace increased gradually along the section,and the soil pH value and CaCO₃were higher in the 0-40 cm layer.The content of soil AP,OM and TN in dam land and terrace was significantly higher in the 0²0 cm layer than in other layers?P<0.05?,the soil AK content of dam land was significantly higher in the 0²0 cm layer than in other layers?P<0.05?,and the dwastribution of soil TP and TK profiles was uniform.In the horizontal dwastribution,the soil texture of back in dam was larger,and the soil OM and TK content were significantly higher?P<0.05?,the soil MWD of the down slope terrace was larger,the TA was small,the soil CaCO₃ content was significantly smaller?P<0.05?,and the difference of other soil nutrients was not obvious.?2?From 2006 to 2016,the content of total soil water-stable aggregate content in dam land increased slightly,the content of soil water-stable aggregate content in terrace decreased,the average mowasture content increased,and the soil total porosity of dam land and terrace decreased,and the permeability became worse.The content of soil CEC in dam land and terrace increased,the soil CaCO₃ and pH value decreased significantly,the content of soil AP and AK increased obviously,and the content of soil TP decreased obviously,soil OM and TN content in dam land increased slightly,and the terrace was the opposite.With the increase of land use life,there was a trend of degradation of soil nutrients as"first increase and then decrease".The critical year of dam land was about 45,and the critical year of terrace was about27 years.At present,there is a lack of OM,N and P in dam land and terrace in the study area.The content of K is abundant.It still faces the trend of salinization.Under different land use modes,the soil nutrient status of woodland and farmland is better than that of grassland.?3?SOM was significantly related with fine clay,coarse clay,sand grains,texture roughness,TA,MWD and WC.SOM was of significantly correlation with AP,AK,TN,TP,TK,CEC and CaCO₃ was significant,revealing that OM plays a central role in soil fertility change.Soil potassium acted as a link between soil nutrient properties and soil chemical properties.The AP,OM,TN,pH,CEC and CaCO₃ were significantly correlated with smaller particles.