Characteristics Of Runoff And Sediment Of Tobacco Planting Soil On Purple Soil Slope Farmland Based On Soil Moisture Changes

Soil erosion is one of the major crises facing human living environment in the world today.China is one of the countries with the most serious soil erosion in the world.Liangshan Prefecture is one of the areas with extremely serious soil erosion in my country,and one of the most suitable producing areas for high-quality flue-cured tobacco in my country.In order to explore the characteristics of soil erosion on the purple soil slope farmland and provide a scientific basis for tobacco-growing soil management,this study took the tobacco-growing slope farmland in Huidong County,Liangshan Prefecture as the research object,and measured different slopes（5°,10°,15°,20°,25°,and 30°）field outflow plots to carry out long-term positioning observations,to study the change characteristics of water content of different soil layers（10,20,30,40,60 and 100 cm）under rainfall conditions,to discuss slope,rain intensity,and early stage Soil erosion characteristics of tobacco-growing slope farmland affected by water content and farming measures.The main findings are as follows:（1）Rainfall distribution in the study area is extremely uneven during the yearThrough the analysis of rainfall data in the past 10 years,the distribution of rainfall in the study area during the year is extremely uneven.The rainfall from June to September accounts for 80.2～92.5%of the annual rainfall;moderate to heavy rain accounts for 80.7%of the total rainfall from June to September.An important reason for high erosion intensity.（2）The vertical change of water content of different soil layers and the horizontal change of water content of the same soil layer are quite differentThere are significant differences in soil moisture content between different slopes and soil depths（P<0.05）.Under different slopes,as the depth of the soil layer increases,the soil moisture content presents an increasing trend,and its coefficient of variation basically shows a decreasing trend.The coefficient of variation of soil moisture content of 10～60 cm is between 10.63～50.78%.Medium variation.The moisture content of the 100 cm soil layer is between 5.10%and 8.71%,which is a weak variation.Under different soil depths,the soil moisture content basically decreased with the increase of slope under the downhill ridge cultivation,and 5°was obviously greater than 15°and 25°in the cross-slope ridge cultivation plot.（3）Rainfall has a significant impact on soil moisture contentRainfall can significantly increase the soil moisture content of each soil layer and reduce the difference of soil layers;rainfall makes the coefficient of variation of soil moisture content of 30～100 cm soil layer significantly increase,and the increase increases with the increase of soil depth;rainfall affects the soil The depth and time of the influence of moisture content increase with the increase of rainfall intensity.（4）The previous water content,rain intensity and slope all have a significant impact on the change of runoff coefficient and sediment yieldThe runoff coefficient increases with the increase of the previous water content;The sediment yield shows two changing trends with the increase of the previous water content.The previous water content in the plots of 5°,10°,15°and 20°is between13.7 and 26.8%,and the sediment yield increases with the previous water content.The water content in the 25°and 30°plots is only between 7.5 and 11.7%,and the sediment yield decreases with the increase of the previous water content..The runoff coefficient and sediment yield increase with the increase of the maximum 30 min rainfall intensity(I₃₀),and the change of sediment yield with I₃₀is affected by vegetation coverage.Under light rain（0.14～0.46 mm/min）,moderate rain（0.54～0.88mm/min）,heavy rain（1.1～1.9 mm/min）,the runoff coefficient increases with the increase of slope,the critical slope of sediment yield With the change of rainfall intensity,the critical slope of sediment yield changes under light rain and moderate rain is 20°,the maximum sediment yield is 113.8 t/km²and 193.5 t/km²,and the critical slope under heavy rain is 25°.The amount of sand is 389.1 t/km².（5）Reasonable farming measures can slow down the degree of soil erosionUnder different slopes and soil depths,the cross-slope ridge farming plot has a higher soil moisture content and a smaller coefficient of variation,indicating that the cross-slope ridge farming has stronger water storage capacity and better water retention;the runoff coefficient and The sediment yield is significantly lower than that of the downhill ridge farming community.The cross-slope ridge cultivation has a higher flow and sediment reduction benefit.The benefits of runoff and sediment reduction are between 4.4～41.7%and 13.4～80.4%,with I₃₀and slope The increase and decrease.