Research On The Impact Of Land Use Change On Soil In The Loess Plateau

This dissertation is based on the case study of typical cultivated land transforming into apple orchard in Luochuan tableland in the Loess Plateau.Through data collection,field study and type section sampling,soil micromorphology techniques and methods,and laboratory assay and analysis,this dissertation studies the composition,property and micromorphology features of apple orchard transformed from cultivated land and apple orchard soil of 20-60 years in Luochuan tableland,the coupling relationship between land use change and the land use age,and the evolution of soil fabric,soil property and soil function.It also provides scientific evidence for the rational utilization of land resources in the Loess Plateau and the sustainable development of economy and ecological environment.Conclusions of the study are as followings:1)After the transformation from cultivated land to apple orchard,the soil profile configuration has changed from arable soil profile configuration Ap/(Ap1-Ap2)-Bc-A-Ck-C to apple orchard soil profile configuration AB-Bc--A-Ck-C?2)The land use change has a significant effect on the physical and chemical properties of soil,and the effect tendencies are different in different soil depth.After the transformation,In the soil layer of 0-20cm,there is a notable increase in soil clay content,volume-weight and moister content,and a notable reduce in soil total porosity,magnetic susceptibility and the content of CaCO3.There is no significant change in the content of sand.In the soil layer of 20-40cm,the total porosity increases signally,and the volume-weight,magnetic susceptibility and pH reduce signally.In the soil layer of 40-60cm,the volume-weight and magnetic susceptibility reduce significantly.In the soil layer of 60-80cm,the content of CaCO3 increases markedly.There is no significant change in soil property in the soil layer of 80-100cm.Along with the extension of the use time of the apple orchard,the volume-weight of soil increases,and the clay particle and moisture content increase firstly and then reduce,and the value reaches to its maximum at 40a(few of them at 20 a),while the magnetic susceptibility,the total porosity and CaCO3 show a tendency of reduction.3)The land use change has a notable effect on the change of soil nutrient.After the transformation of cultivated land into apple orchards.In the soil layer of 0-20cm,soil organic matter and the contents of total nitrogen,total phosphorus,total potassium and rapid available potassium increase significantly;the contents of soil rapid available phosphorus reduce obviously;in the soil layer of 20-40cm,soil organic matter and the contents of total nitrogen,total phosphorus increase significantly,while the contents of total potassium and rapid available phosphorus reduce obviously;in the soil layer of 40-60 cm,the contents of soil organic matter,total nitrogen,total phosphorus,available nitrogen increase significantly;while soil total potassium,rapid available phosphorus decrease significantly;in the soil layer of 60-80 cm,the contents of soil organic matter,total phosphorus and available nitrogen increase significantly,while the contents of total potassium and rapid available phosphorus decrease significantly;in the soil layer of 60-80 cm,there is no significant change in most of the contents of the soil nutrient.With the extension of land use age,the contents of the soil organic matter,total nitrogen,total phosphorus,rapid available phosphorus,rapid available potassium show the tendency of increase firstly and then reduce,and the value reaches to its maximum at 40a(few of them at 20 a);and there is no obvious change in the contents of soil total potassium and available nitrogen.4)The land use change has a prominent effect on the change of the components of soil.After the transformation of cultivated land into apple orchards.In the soil layer of 0-20 cm,the contents of soil constant elements like SiO2,Al2O3,Fe2O3,and the microelements like Mn,Cu,As,Co,Zn and Pb increase significantly;while the contents of MgO,CaO,Na2O,Cr,reduce obviously,in the soil layer of 20-40cm,the contents of Fe2O3,Na2O increase significantly while there is no significant change in the content of constant elements and micro elements of the soil;in the soil layer of 40-60 cm,the contents of CaO,Na2O increase significantly,while the contents of SiO2,Al2O3,Fe2O3,MgO,Mn,Cr,Ni,Cu,Co and V reduce significantly;in the soil layer of 60-80 cm,the contents of CaO increase significantly while the contents of SiO2,Fe2O3,MgO,Mn,Cr and Cu reduce significantly;in the soil layer of 60-80 cm,there is no significant change in the contents of most of the elements.With the extension of land use age,there will be no obvious change in the constant and micro elements of the soil.5)The land use change has a remarkable effect on the soil micromorphology,and the effects are different in different soil layers.After the transformation of cultivated land into apple orchards.In the soil layer of 0-20 cm,soil aggregate changes from finely granular structure into multi-level aggregates,and the pore becomes bigger,and the wall of the pore becomes smoother,all of which reflect a much stable soil environment of the apple orchard soil compared with the cultivated;the wall of the pore firstly increases and then reduce with the extension of use age of the apple orchard soil,and it reaches its maximum value at 40a;the tendency of smaller and rounder coarse grain soil micro morphological becomes less obvious;and the clay content,secondary calcite,humus setting group,carbonized substance,and animal dung increase;In the soil layer of 0-20 cm,the spherical soil aggregate is much more developed,and the porosity,pore wall smoothness,and pore diameter increase significantly;the roundness of the coarse particle reduces,while the C/F10?m value increases;clay content and calcite crystals increase,and the decomposed and semi-decomposed plant residues,black carbonized substance,soil animal fecal pellet increase significantly;with the extension of apple orchard land use age,the soil micromorphological features mentioned above will increase first and then reduce,and reach the maximum value at 40a.In the soil layer of 40-80 cm,soil aggregate increases,and the pore roundness,pore wall smoothness increase significantly;the roundness of the coarse particle reduces,but with the extension of apple orchard land use age,there will be no obvious change rule in soil pore morphology;clay content increases,and the secondary calcite grows,with the extension of apple orchard land use age,the content of large number of white secondary carbonate shows a increase tendency;while there is no significant changes in the soil coarse particle morphology.In the soil layer of 80-100 cm,there is no significant changes in the soil aggregate and porosity,soil coarse particle,and soil formation,and so does when the use age of apple orchard land extends.6)Soil function gets strengthened after the change from cultivated land into apple orchard.Soil production function and ecological function are much strengthened after the change.For example,in the soil layer of 0-20 cm,the production function index increased by 38.44%,but no significant change is found in the soil layer of 20-100 cm;soil ecological function index is increased from 65.69%to 70.00%with a increase of 6.55%,and the increase is detected in all the soil layers;with the extension of apple orchard land use age,both the production function and ecological function increase first and then reduce,and reach the maximum value at 40a;soil quality increases significantly,in the soil layer of 0-40 cm,soil quality index(SQI)increases by 14.53%,but no significant change is detected in the soil layer of 40-100 cm;with the extension of apple orchard land use age,the SQI increases first and then decreases,and reaches its maximum at 40a and minimum at 60a,which means that the orchard soil quality is best at 40 a and worst at 60a.Although the cultivated land soil and apple orchard soil are affected by both natural conditions and human activities,human activities play a leading role during the development process.After the transformation,significant changes occurred in terms of the influencing process towards land made by human activities are listed below:The soil properties are affected by fruit growing and management activities,rather than agricultural cultivation activities.The vegetation form changes from herbaceous plants(corn and wheat etc.)to woody plants(apple tress).The year after year farming activities(tillage,turn,plow,harrow and other activities)are replaced by the growth of apple trees' roots and orchard management activities.The organism's influence depth on soil increases from 35cm to 80cm.The dense plow pan between 20-35cm has been damaged gradually.The frequent periodic crop dusting and chemical fertilizer have changed from applying on the ground to underground(20-35cm).Because of economic comparison,the fertilizing amounts are different,and the soil-forming process of cultivated soil has been replaced by that of the orchard soil.All the changes stated above have changed the soil environment significantly,and changed the presence modes,conversion and transport process and accumulation spatial position of substances in soil,which can lead to the inevitable differentiation of soil properties and construction.And then the evolution of soil function happens.The continuous use time of the apple orchard intensifies the degree of differentiation.