Effects Of Typical Torreya Grandis Intercropping Systems On Soil Physicochemical Properties On Sloping Farmland In The Three Gorges Reservoir Area

The Three Gorges Reservoir area has loose geology,abundant rainfall,more people and less land,and unreasonable land use,resulting in serious soil erosion and serious decline in land productivity.In recent years,in order to control soil erosion and improve soil fertility,Torreya grandis intercropping systems have been widely used in slope farmland in the reservoir area.Therefore,it is particularly important to study the effects of different Torreya grandis intercropping systems on soil physical and chemical properties and soil fertility quality evaluation in this area.Three typical intercropping systems,Torreya grandis(TG),Torreya grandis-Polygonatum sibiricum(TGP),and Torreya grandis-Glycine max(TGG),were selected in the Torreya grandis planting bases located in Baoping Town,Yunyang County,Chongqing.By combining field sampling and indoor measurement methods,the variation of soil physical and chemical properties under each mode was analyzed,the correlation between physical and chemical indicators was explored,and the comprehensive score of soil quality under each model was evaluated and ranked by using principal component analysis(PCA)and soil fertility quality index method.The results of the experiment provide a theoretical basis for the improvement of soil quality in the Three Gorges Reservoir area and for the extension and application of agroforestry compounds.The main study achievements are as follows:(1)TGG has the lowest soil bulk density and the highest total soil porosity,maximum water holding capacity and capillary capacity.Compared to TG,TGG has a5.84%lower bulk density;the total porosity,maximum water holding capacity and capillary capacity have increased by 12.99%,32.78%,and 6.90%,respectively.The stable soil infiltration rates of TGP and TGG were 2.07 and 2.97 times higher than those of TG,respectively.The results of regression fitting analysis of infiltration process show that the general empirical model has the best fitting effect on the infiltration process,and the R~2values were between 0.939-0.982,which is more suitable for describing the infiltration characteristics of soil water in the study area.(2)The highest content of soil micro-aggregates was found in the 0.25-0.05 mm soil micro-aggregates and the lowest in the 2-0.25 mm soil micro-aggregates in all models.Both fractal dimensions(D)and proportion of characteristic soil micro-aggregates(PCM)exhibited TGG>TGP>TG.Compared to TG,PCM increased by 20.83%and 122.92%for TGP and TGG,respectively;D increased by 0.38%and1.89%,respectively.Regression analysis showed that D was highly significantly positively correlated with 2-0.25,0.02-0.002,and<0.002 mm soil micro-aggregates,and highly significantly negatively correlated with 0.25-0.05 mm soil micro-aggregates.PCM was significantly positively correlated with all particle size soil micro-aggregates except for 0.25-0.05 mm soil micro-aggregates,which was highly significantly negatively correlated with all other particle sizes.(3)TGG showed the highest soil p H and electrical conductivity(EC)among the different Torreya grandis intercropping patterns,with 42.35%and 190.14%increase in soil p H and EC,respectively,compared to TG.Different Torreya grandis intercropping patterns had different degrees of increase in soil organic carbon and nutrient content.Compared to TG,TGG was the most effective in increasing soil organic carbon and nutrient content,with soil organic carbon(C),total nitrogen(TN),total phosphorus(TP),total potassium(TK),available nitrogen(AN),available phosphorus(AP)and available potassium(AK)increasing by 13.63%,42.86%,35.90%,22.96%,66.70%,224.98%and20.94%,respectively.Soil C:N,C:P,and N:P under the three systems were below the national average values(14.4,136,9.3),with 8.39-10.73,31.63-45.22 and 3.25-5.61.And the N:P ratio was less than 10,indicating that N was the limiting nutrient in the study area.(4)The correlation analysis results between soil physicochemical properties under different Torreya grandis intercropping modes indicate that:Soil bulk density was positively correlated with capillary porosity,C:N,and AN:AP,but negatively correlated with non-capillary porosity,maximum water holding capacity,available nitrogen,electrical conductivity,total N,available P and AP:AK;Total porosity was positively correlated with p H,total P,AP:AK,electrical conductivity,but negatively correlated with C:P,AN:AP.Maximum water holding capacity was positively correlated with p H,electrical conductivity,total P,available N,available P,AP:AK,available K,and only negatively correlated with AN:AP;Soil p H and electrical conductivity were all positively correlated with available N,available P,available K,AP:AK,total N,and total P,and only negatively correlated with AN:AP;Total N was positively correlated with total K,available N,available P,available K and AP:AK,but negatively correlated with C:N and AN:AP.The correlations between the above indicators all reached a significant level(P<0.05 or P<0.01).(5)The principal component analysis(PCA)and soil fertility quality integrated indexs under different intercropping patterns and soil depths were ranked as follows:TGG(0.518)>TGP(0.372)>TG(0.253).In summary,reasonable Torreya grandis intercropping systems can effectively improve the physical and chemical properties of soil,which is of great significance to improve soil fertility and enhance soil and water conservation benefits.The TGG model in the study area has the best effect on improving soil quality.