Response Of Purple Soil Erosion Resistance To Different Tree Species Under Soil Matrix Improvement In Central Hunan

Purple soil is one of the main soil types in Hunan Province,which is mainly composed of calcareous purple soil,distributed in many contiguous areas and concentrated in Hengyang Basin in the middle of Hunan Province(hereinafter referred to as the central hilly area of Hunan Province,the same below),with an area of about 46.7×103 km2.Due to the special soil conditions and the influence of human activities,the soil erosion in this area is serious,soil erosion and geological disasters occur frequently,and vegetation restoration is extremely difficult,which seriously restricts the economic development of this area.In this study,the unmodified soil matrix in Hengyang purple soil slope difficult to be afforested was taken as control land.Combined with field investigation and indoor analysis,the comprehensive effects of modified soil matrix and 4 tree species(Cupressus funebris,Liquidambar formosana,Melia azedarach and Koelreuteria paniculata)on erosion durability of soil were studied by principal component analysis.The main characteristics and their influencing factors of purple soil erosion durability in the central hilly area of Hunan Province were expounded,which provides scientific basis for the formulation of soil and water loss control plan and the restoration,construction and optimization of plant community in purple soil slope of the central hilly area of Hunan Province.The main results are as follows:(1)After soil matrix improvement,the volume-weight and pH value of soil decreased,but the difference was not significant compared with the control land;the content of SOC,TN,TK and TP in 0-20cm soil layer increased by 63.94%,103.65%,273.91%and 103.86%compared with the control land,respectively;the anti-corrosion index in 0-10cm soil layer was 1.27 times of that in the control land,and the difference was significant;the content of dry sieve aggregate with>5 mm and>0.25mm increased significantly,while the content of dry sieve aggregate with 0.25-0.5mm decreased significantly;The content of waterstable aggregate with>0.25 mm in 0-10 and 10-20 cm soil layers increased by 19.56%and 9.81%respectively,and the percentage of silt and clay increased by 3.16%-6.07%and 25.21%-5.71%respectively,and the percentage of clay was significantly different compared with the control land,and the percentage of sand decreased by 2.16%-3.29%,respectively;the content of micro-aggregate with 0.05-0.25 mm increased significantly;the damage rate of 0-10 and 10-20 cm soil layer structure decreased significantly,by 11.55%and 4.84%respectively,and the content of micro-aggregate with<0.05 mm decreased;dry sieve aggregate with>0.25 mm,waterstable aggregate with>0.25 mm,structure damage rate,clay,slit,sand,soil anti-corrosion index were significantly positive or negative correlation with SOC,TN,TK,TP,volume-weight.There are 13 main evaluation indexes affecting the soil anti-corrosion of purple soil in the central hilly area of Hunan Province,including dry sieve aggregate with>0.25 mm,waterstable aggregate with>0.25 mm,structural damage rate,clay,slit,sand,SOC,TN,TK,TP,micro-aggregate with<0.05 mm,micro-aggregate with 0.05-0.25 mm and soil anti-corrosion index.After the improvement of soil matrix,the comprehensive anti-corrosion indexes of 0-10 and 10-20 cm soil layers increased by 322.24%and 140.49%compared with the control land,respectively.The results showed that the improvement of soil matrix significantly improved the physical and chemical properties of soil,significantly improved the structural stability of purple soil,and enhanced the erosion durability of soil.(2)Under two different soil matrix treatment methods,the change trends of rhizosphere soil anti-corrosion index,SOC content,root biomass,dry sieve aggregate with>0.25mm,waterstable aggregate with>0.25mm,percentage of clay content and micro-aggregate with 0.05-0.25mm for 4 tree species were basically consistent,all of which showed that:Koelreuteria paniculata and Melia azedarach were higher than that of Liquidambar formosana and Cupressus funebris;the percentage of slit content showed that:Cupressus funebris>Melia azedarach>Liquidambar formosana>Koelreuteria paniculata;the structural damage rate,sand and microaggregate with<0.05 mm content showed that Liquidambar formosana,Cupressus funebris were higher than Koelreuteria paniculata and Melia azedarach;the interaction between soil matrix treatment and tree species had significant influence on dry sieve aggregate with 0.25 mm,wet sieve aggregate with>0.25 mm,percentage of clay content,SOC content and anti-corrosion index.Rhizosphere SOC content and root biomass(except for Cupressus funebris)were positively correlated with dry sieve aggregate with>0.25 mm,wet sieve aggregate with>0.25 mm,clay percentage and soil anti-corrosion index respectively,and negatively correlated with structural damage rate and micro-aggregate with<0.05 mm.The comprehensive index of rhizosphere soil erosion durability in the 4 tree species of the control land was as follows:Koelreuteria paniculata(1.182)>Melia azedarach(-1.067)>Liquidambar formosana(-2.722)>Cupressus funebris(-11.228);the soil matrix improvement land was as follows:Melia azedarach(4.081)>Koelreuteria paniculata(3.397)>Liquidambar formosana(1.565)>Cupressus funebris(0.615).The results showed that the rhizosphere SOC content and root biomass significantly affected the soil anti-corrosion index,Koelreuteria paniculata had the greatest improvement on the erosion durability of soil,followed by Melia azedarach in the control land;Melia azedarach had the greatest improvement on the erosion durability of soil,followed by Koelreuteria paniculata,so it was suggested that Melia azedarach and Koelreuteria paniculata could be selected as the main species for soil and water conservation,vegetation restoration and reconstruction of purple soil slope in the central hilly area of Hunan Province.