黄土高寒区小流域土壤饱和导水率和土壤密度的分布特征

Distribution characteristics of soil saturated hydraulic conductivity and soil bulk density in a small watershed in the alpine zone of the Loess Plateau

为了明确土壤饱和导水率K s和土壤密度ρs对小流域土层深度、坡向、坡位的响应,在黄土高寒区典型小流域选取退耕年限相同的林地采用网格法布设72个样点,按20 cm深度间隔挖取0~60 cm各土层原状土样,利用烘干法和定水头法对ρs和K s进行测定并分析。结果表明:1)小流域内K s属于中等变异程度,ρs属于弱变异程度,均符合正态分布,且存在显著负相关性;K s和ρs与土壤孔隙状况和机械组成均有显著相关性。2)K s在流域内随土层加深逐渐减小,ρs则随土层加深呈增大趋势,差异性均不显著(P>0.05)。3)沿坡面向下K s呈增大趋势,ρs则逐渐减小。4)K s在不同坡向表现为北坡>南坡>东坡,ρs总体表现与之相反的规律,不同坡向、不同坡位间差异显著(P<0.05),即流域内沿坡面向下土壤导水性能增强,北坡、南坡土壤导水性能优于东坡。

[Background]Soil saturated hydraulic conductivity K s and bulk densityρs under different soil depth,slope positions and slope aspects have important effects on soil water distribution and rainfall infiltration in the catchment.However,few reports on this issue in the alpine zone of the Loess Plateau are available.[Methods]In order to clarify the response of two soil physical parameters(ρs and K s)to soil depth,slope aspects,and slope position of small watershed,72 sample points were selected in typical small watershed of this region by grid sampling method.The undisturbed soil cores of 0-60 cm soil layers were taken at intervals of 20 cm depth.And the data of K s andρs were determined by the constant water-head method and oven-drying method,and then were analyzed using classical statistics and variance analysis.[Results]1)In small watershed,the K s was 1.018 mm/min in moderate variability,and theρs was 1.257 g/cm 3 in weak variability,all of them had a normal distribution,and there was a significantly negative correlation between K s andρs.Meanwhile,K s andρs both were significantly correlated with soil porosity and soil particle-size distribution.The correlation between K s and sand content was the highest,but the correlation coefficient was only 0.276.The correlation coefficient betweenρs and total porosity and capillary porosity were the largest,both of which were greater than 0.890.2)The series for K s according to soil depth was:1.20 mm/min(0-20 cm)>1.09 mm/min(20-40 cm)>0.84 mm/min(40-60 cm),with a moderate degree of variation and no significant difference(P>0.05).Theρs increased with the deepening of soil layer and was the degree of weak variation and no significant difference(P>0.05).3)The mean value of K s was as follows:lower position(1.17 mm/min)>middle position(1.21 mm/min)>upper position(0.75 mm/min),andρs mean value was upper position(1.29 g/cm 3)>middle position(1.24 g/cm 3)>lower position(1.22 g/cm 3)in different slope positions.4)The order of K s in different slope aspects were as follows:north-facing slope(1.34 mm/min)>south-facing slope(1.26 mm/min)>east-facing slope(0.53 mm/min),while the overall performance ofρs was opposite to K s.And the value ofρs was:north-facing slope(1.21 g/cm 3)<south-facing slope(1.25 g/cm 3)<east-facing slope(1.28 g/cm 3).There were significant differences between different slope aspects(P<0.05).[Conclusions]Soil water conductivity enhanced from top to the bottom of the slope,and was the best in the north-facing slope and the worst in the east-facing slope,but there was no significant difference with the deepening of soil layer in the small watershed.