宁南黄土区中庄小流域土壤密度坡面变化及尺度效应OA北大核心

[Objective]The aims of this study are to analyze the variation characteristics and scale effect of soil bulk density on slope,to discuss the scale transformation path of soil bulk density on slopes,and to provide theoretical basis for accurate monitoring of soil bulk density,scientific evaluation of soil function and guidance of soil resource management.[Methods]In Zhongzhuang small watershed in the semi-arid loess hilly region of southern Ningxia,three typical slopes after returning farmland to forest and grassland were selected,and five plots were set up from top to bottom according to the slope position.The vegetation types,land use and site conditions of each plot were investigated,and the soil bulk density at 200 cm depth was measured by ring knife method.[Results]In the east slope,west slope and south slope,the soil bulk densities increased linearly with the deepening of soil layer,and the soil bulk densities increased by 0.006 2,0.003 6 and 0.007 5 g/cm3 for every 10 cm deepening of soil layer,which was due to the difference of soil layer of vegetation root,soil organic matter and compaction.In the 0-200 cm soil layer,the mean soil bulk densities on the eastern and southern slopes were 1.22 g/cm3,which was lower than that on the western slope(1.26 g/cm3).There were differences in the slope changes of soil bulk density on the three slopes.The changes along the slope of the eastern slope,the western slope and the southern slope showed a gradual increase or first increase and then decrease,first increase and then decrease,and first decrease and then increase.On the whole,soil bulk density in the lower part of the slope was larger than the upper part.The main reasons included slope differences such as vegetation type,land use,human activities,and recovery years.The slope scale effect was evaluated by the change of the slope sliding average value of soil bulk density at a horizontal distance of 100 m from the top of the slope.The average soil bulk density slope scale effects of 0-200 cm soil layer was 0.032(g/cm3)/100 m on the eastern slope,0.024(g/cm3)/100 m(0-250 m from the top of the slope)and-0.007(g/cm3)/100 m(250-329 m from the top of the slope)on the western slope,-0.011(g/cm3)/100 m(0-140 m from the top of the slope)and 0.018(g/cm3)/100 m(140-368 m from the top of the slope)on the southern slope.The relationship between the ratio of soil bulk density of each soil layer and the mean value of the slope in different slope positions of the three slopes was constructed(R2＞0.80,p＜0.0001).The relative errors of the slope mean of soil bulk density predicted by the fitting relationship were all less than 2.5％,so that the mean value of the slope could be accurately and conveniently estimated by the soil bulk density measurement value of any slope position.[Conclusion]There are obvious differences of soil bulk density in slope change and slope position in semi-arid loess area,and vegetation type,human disturbance and land use have great influence on slope distribution pattern of soil bulk density.In the future,the contribution of main factors to soil bulk density change on slope and scale effect of should be strengthened.