| The physical and chemical properties of soil and water retention characteristics of litter in karst area under different restoration years were studied by field sampling and laboratory analysis.The spatio-temporal replacement method was used to collect 5 a(grassland),10 a(shrub),20 a(shrub),40 a(forest)and cultivated land as the control soil and litter samples in Pingba District,Anshun City,Guizhou Province.The physical and chemical properties of the samples were measured,and the differences of the physical and chemical indexes and litter indexes of the soil profile and their changes with the restoration years were analyzed.The main conclusions are as follows:(1)With the extension of restoration years,the sand content in each soil layer increased first and then decreased,the silt and soil bulk density decreased first and then increased,and the clay content decreased first and then increased and then decreased.Soil total porosity,capillary porosity,non-capillary porosity,water content,saturated water holding capacity and capillary water holding capacity all showed an increasing trend.In the vertical soil profile,sand,silt,total porosity,capillary porosity,non-capillary porosity,saturated water holding capacity and capillary water holding capacity all decreased with the increase of soil depth.On the contrary,clay content,bulk density and water content increased with the increase of soil depth.(2)With the extension of restoration years,the contents of soil organic matter,total nitrogen,alkali-hydrolyzed nitrogen and available potassium in each soil layer showed a gradual increasing trend.The differences between cultivated land and restored 5 a(grassland)were not great,but were significantly lower than the last three restoration stages due to the short return time.Soil p H and total phosphorus available phosphorus decreased first and then increased.The soil total potassium increased first and then decreased.In the vertical soil profile,soil p H of cultivated land and restored land increased with the increase of soil depth.The contents of other nutrient indexes decreased with the increase of soil depth.(3)With the extension of restoration years,the content of available Fe,Mn and Cu in all soil layers decreased first and then increased and then decreased,while the available zinc decreased first and then increased.In the vertical soil profile,the content of available trace elements in the 0～20cm soil layer was generally higher than that in the 20～40 cm soil layer,showing a certain surface aggregation.The single availability index of Fe,Mn and Cu was greater than 1 at different restoration years,while the availability index of Zn was greater than 1 only at the restoration stage20 to 40 years.The comprehensive effectiveness index from large to small is CK,20 a,5 a,40 a,10a in turn,showing a trend of first decreasing,then increasing and then decreasing with the increase of recovery years.(4)Soil bulk density was negatively correlated with organic matter,alkali-hydrolyzed nitrogen,sand content,porosity,water content and water holding capacity.Soil organic matter is positively correlated with P,Mn and Zn elements,but negatively correlated with soil porosity and water holding capacity.According to the cluster genealogy diagram of cultivated land and the restoration years,the soil physical and chemical properties of grassland and cultivated land in the restored 5years were similar,which could be classified into the same category.The physical and chemical properties of soil restored for 10～40 years are quite different from those of grassland and cultivated land restored for 5 years,and can be classified into another category.The changes of physical and chemical properties of soil in the process of vegetation restoration mainly occurred within 10～40years after the return of farmland.(5)The litter accumulation in different recovery years increased gradually with the increase of recovery years;The maximum water holding capacity,maximum storage capacity and effective storage capacity increased first,then decreased and then increased with the increase of restoration years,and reached the maximum value significantly at 40 years after returning farmland,with the order of 40 a>10 a>20 a>5 a.The maximum water retention rate and maximum storage rate decreased first and then increased,with the order of 5 a>10 a>40 a>20 a,and each index showed the semi-decomposed layer>undecomposed layer.There was a significant logarithmic function relationship between litter water holding capacity and soaking time:Q=aln(t)+b(R~2>0.905),and a significant power function relationship between water absorption rate and soaking time:V=at~b(R~2>0.962),both of which showed a good correlation.The comprehensive study showed that vegetation restoration not only increased the bioaccumulation and rainfall interception of litter layer,but also improved the soil structure and pore status,as well as the soil water holding performance and soil nutrient function in karst areas compared with the initial period of farmland conversion.The results have important influence on soil and water conservation function and soil nutrient function in karst area. |
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