Research On Soil Erosion And Nutrient Loss Under Different Farming Measures From Slope Field

The experiments were carried out at Tuanjie Village,Jiuxian Town,Malong County,Qujing City, Yunnan Province,China,in 2008.The monitoring method of fixed position of runoff plots was used to study the loss amounts of soil,water and its nutrinet of the runoff process of natural minfaU in red soil slope field.The experiments were conducted to study the influence of different farming measures on the runoff process and the loss,the changes of soil nutrient content,the yield and quality of tobacco leaves. The main results obtained were as the following:In earlier period of the process of soil erosion,the main factor effected on soil erosion and nutrient loss were farming measures.When tobacco growth entered the mature period,the vegetation cover of various farming measures reached maximizing,those tobacco leaves could effectively reduce rainfall erosion force.The farming measures of contour tillage could effectively slow down the erosion force of heavy rain,not effectively reduce runoff in long rain.The farming measures of contour tillage were better than slope tillage in runoff regulation.The variation coefficient of different farming measures was nutrient loss＞silt loss＞runoff amount＞rainfall amount.Rainfall is the premise which the runoff produces,the silt loss is follows the runoff production,the nutrient loss is follows the runoff and silt loss production.The variation coefficient of rainfall formed the basis of the variation coefficient of runoff,the variation coefficient of runoff formed the basis of the variation coefficient of silt loss,the variation coefficient of runoff and silt loss formed the basis of the variation coefficient of nutrient loss.The variation coefficient of various loss were increased by stages which was referred to magnifying effect of variation coefficient.In YunNan red soil slope field,the comprehensive farming measures of contour tillage + straw mulching + uncovering plastic film was the best to control runoff amount,silt and nutrient loss in rainfall - runoff process.The loss of nitrogen and phosphorus mainly through particle were 90%of the total.The loss of dissovlved NH₄⁺-N and NO₃^--N not only were affected by rainfall and farming measures,but also by absorption characteristics of different nitrogen form at different growing stage in tobacco,conversion ways and transformation time of nitrogen,and adsorption characteristics of nitrogen in soil.The loss of NH₄⁺-N and NO₃^--N in runoff could not reliably represent the effection of farming measures.All kinds of farming measures showed that the loss of phosphorus was less than nitrogen,the ratio of nitrogen to phosphorus in runoffvaryed in a certain range.Soil erosion and fertilizer application made soil acidified in slope field,soil acidification increased significantly with depth.The content of soil organic matter,total nitrogen and available nitrogen in the upper soil layer were less than before soil erosion,but in plow pan these content showed increasing trend. Not only did soil erosion effect soil nutrients loss,but also promote soil weathering.The farming measures of uncovering plastic film was able to reduce the loss of nutrients,so this fanning measures could promote tobacco yields.Under the same conditions of nitrogen application,the farming measures of straw mulching absorbs more available nitrogen for straw decomposing,so the tobacco yields in this farming measures was lower.The farming measures of straw mulching increased the proportion of middle and superior tobacco leaves and output value was the highest.