Spatial Heterogeneity Of Soil Physical And Chemical Properties On A Typical Slope In Feldspathic Sandstone Area

The feldspathic sandstone area is widely distributed in the northern part of the Loess Plateau,which is one of the most serious soil erosion areas in the world.Due to the influence of soil forming factors,human activities and other factors,soil physical and chemical properties have a certain degree of heterogeneity,and the degree of heterogeneity and its main influencing factors may be different at different scales,The research on its spatial heterogeneity and its influencing factors can be used as the basis of ecological environment restoration strategy and scientific management of soil resources.Based on this,a typical restored slope of Pinus tabulaeformis was taken as the main research object in this study.Using classical statistical theory and geostatistical theory,the spatial and temporal distribution characteristics of soil moisture,soil organic carbon and total nitrogen at different depths and slope positions and their interaction were analyzed,the main conclusions were as follows.(1)Soil moisture,soil organic carbon(SOC,g/kg)and soil total nitrogen(STN,g/kg)of the slope in the study area had obvious spatiotemporal heterogeneity with an obvious spatiotemporal pattern.Soil mass moisture content(SMMC,%)in 0-2 m layers gradually increased with the increase of soil depth.The range of mean value was 9.93%-13.83%,and the coefficient of variation ranged from 18.68%-39.80%.The result of ANOVA showed that the average SMMC of 0-20 cm was significantly less than that of 140-200 cm(P<0.05).Soil depth and plant characteristics have great influence on the distribution characteristics of SMMC profile.On the time scale,rainfall factors have a great influence on the variation characteristics of soil moisture.The coefficient of variation(>0.1)of shallow soil volume moisture content(SVMC,%)with time was greater than that of deep soil(<0.1),and the variation of deep SVMC was more stable.The range of SOC at different depths was0.74-15.43 g/kg,the range of mean value was 1.59-6.82 g/kg,and the coefficient of variation ranged from 23.78%-45.66%.The values of STN at different depths ranged from 0.03-1.09g/kg,the range of mean value was 0.09-0.54 g/kg,and the coefficient of variation ranged from 28.24%-57.19%.SOC and STN decreased rapidly at first and then stabilized with the increase of depth.SOC and STN had obvious surface aggregation effect.The results of ANOVA showed that SOC and STN were significantly different in different depths.(2)The geostatistical results showed that for SMMC,except for 60-80 cm SMMC with weak spatial dependence,the spatial dependence of SMMC was strong.The spatial differentiation structure of SMMC in most soil layers could be fitted by Gaussian model.The spatial differentiation structure of SOC in most soil layers could be fitted by Gaussian model and linear model,while the spatial differentiation structure of STN in most soil layers can be fitted by Gaussian model.The ranges of SMMC,SOC,and STN at different depths were15.60-91.07 m,23.56-114.60 m,and 16.10-89.90 m,respectively,which were larger than the sampling interval(15 m),indicating that the distribution of sample points could represent the spatial variation structure of SMMC,SOC,and STN on the whole slope.(3)Slope position and soil depth are the main controlling factors of soil physicochemical properties.In 0-20 cm soil layers,the SMMC,SOC,and STN in the middle and low slope were higher than that in the up slope.The results of ANOVA showed that the soil saturated hydraulic conductivity(KS,mm/min)and bulk density(BD,g/cm~3)of different slope positions in the same soil layer were significantly different,and the results of paired sample T-test showed that Ks in different soil layers of the same slope had significant difference(P<0.05).In the up slope,BD in 0-10 cm was significantly less than that in 10-20 cm(P<0.05),while BD in the middle and low slope had no significant difference(P>0.05).The percentage of sand content in the middle slope was significantly higher than that in the low slope,while the percentage of silt content and clay content in the low slope was significantly higher than that in the middle and up slope(P<0.05).For the 10-20 cm soil layer,except that the percentage of clay content in the middle slope was significantly lower than that in the up and low slope(P<0.05),the percentage of sand content and silt content had no significant difference in different slope positions(P>0.05).(4)The correlation between soil physical and chemical properties was significant.SMMC of 0-10 cm layer was positively correlated with SOC and STN(P<0.01),and negatively correlated with altitude(P<0.01),but SMMC of 10-20 cm layer was positively correlated with the percentage of silt content(P<0.01),and negatively correlated with percentage of sand content(P<0.01).SOC had significant positive correlation with STN(P<0.01)in0-10 cm and 10-20 cm,while negative correlation with Ks(P<0.05);in addition,SOC in0-10 cm had significant negative correlation with altitude(P<0.05),and SOC in 10-20 cm had significant positive correlation with clay content(P<0.05).