Effects Of Acidification Degree And Utilization Mode On Clay Minerals,Surface Properties And Carbon Fixation Of Brown Soil

In recent years,soil acidification has become an important factor affecting agricultural production and ecological environment.Acidification mainly occurred in the southern region,mostly caused by natural,such as rainfall leaching.However,the soil acidification problem in northern China was becoming increasingly prominent,especially in Jiaodong Peninsula,which were mainly neutral in the 1980s,and now they were basically acidic soil.At present,most studies focused on soil acidification in southern China,while relatively few studies on soil acidification in northern China.The study of acidified brown soil in Jiaodong will help us to understand the mechanism and harm of soil acidification more comprehensively.In this study,brown soil samples with different acidification degrees（strong acid pH<4.5,acid 4.5<pH<5.5,weak acid 5.5<pH<6.5）and samples with different utilization modes（cultivated land,orchard,forest land and wasteland）were selected from Muping District of Jiaodong Peninsula.The effects of acidification degree of brown soil on clay minerals and surface properties as well as on soil carbon sequestration and carbon components were systematically studied to analyze the effects of clay minerals on surface properties of brown soil,and to explore the reciprocal response between carbon sequestration characteristics and clay minerals and surface properties of brown soil after acidification.The research results were conducive to understand the acidification mechanism of brown soil,and could provide theoretical basis of the treatment and sustainable utilization of acidified brown soil,and provide important information on rational land use planning,improving management level and enhancing soil carbon sequestration potential.The main research results are presented as follows:（1）The composition and content of brown soil clay minerals changed under different degrees of acidification.The main clay minerals of brown soil were illite,kaolinite,vermiculite and chlorite.A small amount of montmorillonite was found in weakly acidic soil（pH 5.5-6.5）,and gibbsite was found in strongly acidic soil（pH<4.5）.Through the correlation analysis of the contents of clay mineral,it can be inferred that when pH>5.5,illite would be transformed to montmorillonite;when pH<5.5,illite would be transformed to kaolinite through vermiculite;when soil acidity reached strong acid level（pH<4.5）,clay minerals would be completely hydrolyzed to gibbsite.（2）pH,clay content and clay mineral types were the main factors affecting soil surface properties.With the increase of acidification degree,the values of CEC_8.2,CEC_P,CEC_m,NC and SSA decreased,while the values of AEC and PZC increased.It was concluded that the change of CEC_Pvalue was caused by the change of soil clay mineral composition of acidification degree,that was,the increase of 1:1 clay mineral（kaolinite）and the decrease of2:1 clay mineral（illite）resulted in the decrease of CEC_Pwith the increase of acidification degree.（3）The CPMI value was the largest when pH values were between 5.5 and 6.5,that was,the weakly acidic soil had the strongest carbon fixation capacity.In 0-20 cm soil layer,the CPMI value of weak acid soil was significantly increased 88.74%,48.92%than that of strong acid and acidic soil.In 20-40 cm soil layer,the CPMI value of weak acid soil was significantly increased 118.57%,161.76%than that of strong acid and acidic soil.In 40-60 cm soil layer,the CPMI value of weak acid soil was increased 29.48%,20.10%than that of strong acid and acidic soil.（4）The acidified brown soil of the four utilization modes all contained illite,kaolinite,vermiculite and chlorite,and the order of the relative content values was:illite>kaolinite>vermiculite>chlorite.The content of organic matter and clay contents were the main factors affecting the content of soil clay minerals,while the content of illite and kaolinite in clay minerals were the main factors affecting the surface properties.Therefore,the CEC_8.2,CEC_P,CEC_m,SCD and NC values were higher in forest land and orchard with high organic matter and clay content.（5）As a whole,the content of organic carbon and its components in forest land and orchard were higher than that in cultivated land and wasteland.Combined with the analysis of carbon pool management index,it was found that the carbon sequestration capacity of the soil in forest land and orchard were higher than those in cultivated land and wasteland.Especially in topsoil,the CPMI values of cultivated land and wasteland were significantly decreased by63.05%and 84.14%compared with orchards,and by 55.35%and 80.83%compared with forest land.（6）The correlation analysis showed that the correlation between CPMI and other factors was significant,so the CPMI could be reflect the acidification degree and utilization modes on brown soil organic carbon quantity and quality more comprehensive and dynamic.It could be used to characterize the stability of the soil carbon reservoir.In summary,the increased of acidification degree would promote the weathering of illite in the brown soil to vermiculite or kaolinite.Under the condition of strong acid,kaolinite would be completely hydrolyzed to a small amount of gibbsite.PH,clay content and clay mineral types were the main factors affecting the surface properties.With the pH value in the range of 5.5-6.5,the brown soil had the strongest carbon fixation capacity.Organic matter and clay content were the main factors affecting the mineral content under different utilization modes,The contents of illite and kaolinite were the main factors affecting the surface properties.Overall,the carbon fixation capacity of forest land and orchard soil were higher than that of farmland and wasteland.