Response Of Soil Cation Exchange Performance To Different Land Use Patterns In Karst Mountainous Area

In this study,different land use types of calcareous soil in the mountainous area of Kras were taken as the research objects,the parameters of soil cation exchange performance were measured and analyzed for six land use types?cultivated land,shrub land,wild grassland,forest-grass intercropping land,forest land and returning farmland to grassland?,the distribution characteristics and variation sources of soil cation exchange capacity and base ions under different land use patterns were studied.The seasonal variation of surface soil cation exchange performance of some land use types was preliminarily studied,and a scientific and reasonable evaluation of soil cation exchange performance of different land-use types was made from the perspective of space and time,it provides scientific basis for the optimization of land use pattern and ecological restoration in the study area.The findings suggest:?1?Profile distribution of soil cation exchange performance under different land use types The CEC of the soil in the study area ranged from 24.34 to 43.99 cmol/kg,and the content of exchangeable base ions showed the law of Ca²⁺>Mg²⁺>Na⁺>K⁺,and Ca²⁺and Mg²⁺dominate?the average proportion of TEB was 92.82%,5.19%?,the proportion of K⁺and Na⁺in TEB was low?average:0.94%,1.05%?.CEC,exchangeable K⁺,Mg²⁺decreased with the increase of soil depth in soil profile,and exchangeable K⁺,Mg²⁺showed different degree of surface aggregation under different land use patterns.The contents of exchangeable K⁺and Mg²⁺in 0-10 cm layer were 30.67%?44.96%and 34.23%?56.24%,respectively.and the phenomenon of surface aggregation was more obvious in forest-grass intercropping.Soil exchangeable Na⁺and Ca²⁺decreased with the increase of soil depth in Shrub land and forest-grass intercropping land.Except shrub land and grassland,other land use types of KSP decreased with the increase of soil depth.All the land use types of MgSP decreased with the increase of soil depth in 0-40 cm depth,and some differences between the layers were significant?p<0.05?.The total average BSP was66.75%.BSP and ESP increased with the increase of soil depth in cultivated land,shrub land,grassland and woodland,and the difference of ESP in forest land was significant?p<0.05?.CaSP increased with the increase of soil depth except forest-grass intercropping.TEB decreased with the increase of soil layer in shrub land,forest-grass intercropping land and woodland.The K/Na range of each land use pattern was0.53?1.79,and it decreased with the increase of soil depth.0-10cm layer in cultivated land was significantly higher than other soil layers?p<0.05?;the distribution of Ca/Mg profile was opposite.?2?The difference of Soil cation exchange performance under different land use types The base ions and saturation of different land use types were different in different soil layers.In 0-40 cm soil layer,CEC,exchangeable Na⁺,exchangeable Ca²⁺,CaSP,TEB,BSP,Ca/Mg were all significantly lower than those in returning farmland to grassland?p<0.05?.and except CEC,other exchangeable base ions and saturation were the highest in woodland.The exchangeable K⁺of cultivated land was significantly higher in0-10 cm layer than that of other land use patterns?p<0.05?,and the exchangeable K⁺of each land use pattern was the highest in the surface layer and near the surface layer.There was no significant difference in KSP and ESP among different land use types.MgSP in 0-20 cm layer showed as returning farmland to grassland>shrub land>forest-grass intercropping land>forest land>wild grassland,and there was significant difference between returning farmland to grassland and wild grassland?p<0.05?.In general,the forest land has better soil fertilization and buffering performance,and the returning farmland to grassland is weak.?3?Seasonal variation of surface soil cation exchange capacity under different land use types The change of surface soil cation exchange performance in different land use types was higher in winter and lower in spring,and the change law with the seasons was from winter to spring,and rose back in summer.The results showed that land use pattern had no significant effect on the seasonal variation of soil cation exchange properties.?4?Factors affecting the cation exchange properties of soils The correlation analysis showed that there were different correlation between the basic physical and chemical properties of soil and the parameters of cation exchange.The organic matter,nitrogen and CEC of all land use patterns were positively correlated?p<0.05?,and the clay particles were positively correlated with the content of base ions?p<0.01?The soil Ph of cultivated land was positively correlated with BSP,KEP,ESP and CaSP?p<0.05?.Therefore,maintaining soil organic matter,regulating soil nutrient content and so on to make the soil base ions to achieve a suitable coordination state is important to improve soil fertility and buffering capacity.