Study On Soil Quality Evaluation And Influencing Factors Of Phoebe Bournei Natural Secondary Forests

Soil is an important part of forest ecosystem,which is the base of forest growth,and can regulate the development and succession of forest communities.Taking the natural secondary forest of Phoebe bournei in Jiangxi Province as the research object,and the data were obtained through the investigation of typical sample plots and the determination of soil samples,and 16 soil physical and chemical indexes were taken as the total data set(TDS).In the study,the descriptive statistical analysis of soil indexes in 0-10 cm and 10-20cm soil layers was carried out,and the correlation between soil indexes in 0-20 cm soil layers was analyzed.The minimum data set(MDS)of soil quality assessment was constructed to evaluate the soil quality,and the main obstacle factors affecting soil quality were determined by using the diagnostic model of index obstacle factors.Finally,the relationship and influence between environmental factors and soil quality were discussed by path analysis.The results can provide reference for the sustainable management of secondary forest of P.bournei and the site selection and management of artificial forest of P.bournei.The main results and conclusions are as follows:(1)Soil moisture(soil water content,maximum water capacity,capillary water capacity and field water capacity),porosity(capillary porosity,non-capillary porosity,total porosity),organic matter,total nutrients(total nitrogen,total phosphorus and total potassium),and available nutrients(available nitrogen,available phosphorus and available potassium)decreased with soil layer deepening.Organic matter,total nitrogen and available nitrogen were rich,total potassium and available phosphorus were in the middle level,while total phosphorus and available potassium were low.The variation coefficient of 16 indexes decreased with soil layer deepening.The variation coefficient of p H value ranged from 5.65%to 6.16%,which had weak variability,while the other indexes had moderate variability,ranging from 10.15%to 64.56%.(2)Except soil water content and capillary porosity,soil bulk density and other physical indexes had significantly negative correlation.Soil water content had significant correlation with capillary porosity and total porosity,and capillary porosity had significant correlation with non-capillary porosity and total porosity.Except p H value,organic matter and other chemical indexes had significantly positive correlation.Total nutrients and available phosphorus had significantly positive correlation,and p H value had significantly positive correlation with total nitrogen,total phosphorus and available potassium.There were significantly positive correlation between total nitrogen and available nitrogen,and between total potassium and available potassium.Except for capillary porosity,there were significant correlations between total nutrients and other physical indexes.There were significant correlations between organic matter,available phosphorus and soil moisture,and between available nitrogen and capillary porosity,total porosity.(3)Through principal component analysis,correlation analysis and Norm value calculation,the minimum data set indexes of soil quality evaluation were field capacity,soil bulk density,total porosity,organic matter,available potassium and total phosphorus.The linear soil quality index(SQI₁-L)was based on the minimum data set ranged from0.157 to 0.711,with an average of 0.443 and a variation coefficient of 36.12%.The nonlinear soil quality index(SQI₂-NL)ranged from 0.319 to 0.654,with an average of0.475 and a variation coefficient of 21.26%.The linear and nonlinear soil quality indexes of the total data set were calculated,and the linear fitting of the soil quality indexes of the total data set and the minimum data set showed that the fitting effect of the linear scoring method(R²=0.866)was better than that of the nonlinear scoring method(R²=0.779),and SQI₁-L was more suitable for the soil quality evaluation of the natural secondary forest of P.bournei.(4)Total phosphorus and soil bulk density were the ma in factors affecting soil quality.The order of obstacle degree was total phosphorus(0.239)>soil bulk density(0.189)>field capacity(0.168)>available potassium(0.151)>organic matter(0.134)>total porosity(0.119).Among them,for the sample plots with poor quality level,the obstacle degree of soil bulk density was larger,which was 0.210.However,in the medium and good quality plots,the obstacle degree of total phosphorus was 0.234 and 0.334,respectively.(5)The order of influencing factors was litter thickness(0.353)>slope position(0.273)>understory vegetation coverage(0.263)>canopy density(0.217).Soil quality increased with the increase of litter thickness,and the soil quality was better when the litter thickness was more than 3 cm.The soil quality increased from up slope to down slope,and the soil quality of middle and downhill was significantly higher than that of up slope(P<0.05).The indirect path coefficients of understory vegetation coverage and canopy density were 0.443 and 0.418,respectively.The soil quality first increased and then decreased with the increase of both.It was better when understory vegetation coverage was60-90%and canopy density was 0.5-0.7.