Variation Characteristics Of The Surface Soil Susceptibility In Liugou Small Watershed Slope Before And After Rainfall

Slope is the basic unit of soil erosion. According to study the variation characteristics of slope surface soil susceptibility and mechanical composition, indicate slope soil erosion and deposition, have the vital significance to soil and water conservation work in the future. Soil magnetism properties is a comprehensive reflection to magnetic particles separate、remove and concentrate, also relate to the soil erosion process. The magnetic tracer method is a new method to study soil erosion. In this study, we use Soil magnetism method, through field investigation%soil sampling and experimental analysis, analyze the variation characteristics of slope surface soil susceptibility and mechanical composition before and after rainfall, discuss the relationship with the slope shape, explore the relationship between variation characteristics of slope surface soil susceptibility and soil erosion in the typical slope from Liugou small watershed. The main results of this study as follows:(1)Slope surface soil susceptibility distribution has distinct differences under two different land-uses. Slope surface soil after high temperature burning in burning forest, soil susceptibility is higher than oil-tea camellia forest. Slope surface soil susceptibility distribution also has differences in the slopes of different slope shapes. Before rainfall, in burning forest, slope surface soil susceptibility distribution present ups and downs in SHA slope, show the highest value in the middle SHT slope, present higher value in the upper SHZ①slope than the lower, also show the highest value in the middle SHZ②slope. In oil-tea camellia forest, slope surface soil susceptibility distribution present decrease trend from upper to lower in YCA slope, show slightly higher value in the upper YCT slope than the lower and show the minimum variation difference in YCZ slope. After rainfall, in burning forest, slope surface soil susceptibility distribution present higher value in the lower SHA slope than the upper, show the highest value in the upper SHT slope, present higher value in the upper SHZ①slope than the lower and present increase trend from upper to lower in SHZ②slope. In oil-tea camellia forest, slope surface soil susceptibility distribution present decrease trend from upper to lower in YCA slope, show obvious higher value in the upper YCT slope than the middle and lower, also show lower value in the upper YCZ slope. Obviously, rainfall conditions affect the slope surface soil susceptibility distribution.(2) Before and after rainfall, slope surface soil susceptibility under different slope type has distinct differences. In the concave slope, from steep slope to gentle slope, surface soil susceptibility decrease in the upper slope, but in the lower slope, SHA slope present significant increase and YCA slope present decrease. In the convex slope, from gentle slope to steep slope, surface soil susceptibility increase in the upper slope, reduce in the middle slope, slightly increase in the bottom slope. In the linear slope, surface soil susceptibility present decrease trend in different slope positions from different types of slope:soil susceptibility decrease in the lower SHZ①slope, decrease in the middle SHZ②slope, decrease in the upper YCZ slope. Variation characteristics of the slope surface soil susceptibility have important relationships with slope shape and gradient.(3)Under two different land-uses, the variation characteristics of slope surface soil mechanical composition under different space parts in slopes of different slope shapes after rainfall also have distinct differences. Since the upper to the lower, in burning forest, clay content firstly decreased and then increased; but sand content firstly increased and then decreased; silt content increase in the middle slope, decrease in other space parts of SHA slope surface soil. SHT slope, clay content firstly increased and then decreased; and sand content firstly decreased and then increased; silt content decreased clearly in the lower slope. SHZ①SLOPE, sand content increase in the lower slope, decrease in other space parts; clay content and silt content increase in the upper and middle slope, decrease in the lower slope. SHZ②Slope, sand content increase in the middle slope, decrease in other space parts; and clay content, silt content decrease in the middle slope, increase in other space parts. In oil-tea camellia forest, clay content and silt content firstly increased and then decreased; sand content firstly decreased and then increased in YCA slope surface soil. YCT slope, silt content decrease in the entire slope; clay content firstly increased and then decreased; sand content firstly decreased and then increased. YCZ slope, clay content firstly decreased and then increased; silt content decrease and sand content increase. In a word, through redistribution of the grain size after rainfall in the slope surface soil can reflect soil erosion or accumulation under different space parts in slopes.(4) After rainfall, there are positive correlation between slope surface soil susceptibility change with clay contend silt content change in soil particles, the correlation coefficient is0.648,0.184; negative correlation with sand content change, the correlation coefficient is-0.630. Especially, the correlation with clay content, sand content change is significant at1percent. There are closely relationship between slope surface soil susceptibility change with clay content, sand content change. Through study slope surface soil susceptibility change, can reflect redistribution of the clay content, sand content in the slope surface soil. This provides a possible method to indicate slope soil erosion.(5) Through compare variation characteristics of slope surface soil susceptibility with variation characteristics of clay content, sand content in mechanical composition before and after rainfall, found it is roughly corresponding under different space parts in slopes of different slope shapes. Surface soil susceptibility decrease, then clay content decrease and sand content increase in surface soil; surface soil susceptibility increase, then clay content increase and sand content decrease. The results showed that study variation characteristics of slope surface soil susceptibility can indicate slope soil erosion or accumulation.