The Analysis Of Characteristics Of Soil And Water Loss And Its Affecting Factors In The Karst Mountainous Farming Area Of Chongqing

The characteristic of Chongqing Karst areas,which is different with the plains karst of Guangxi and the plateau Karst of Guizhou,has its own characteristics.The carbonate rocks solution into the open valley area,non-carbonate rocks weak solution to form a mountain.Chongqing,the formation of karst eco-environment with its own geological, geomorphological and socio-economic background are closely related.There are some ecological vulnerability which lack of Surface water and which became drought;there are some serious soil erosion and soil barren,it also exposed limestone,the rocky desertification becaome seriously;scarce vegetation,and destruction of vegetation as soon as it is difficult to restore.Governance in practice should be based on science to absorb the successful experiences of other regions can not be applied mechanically. According to the actual conditions,it explore the actual situation for the local governance of science and the urgency of the task means,there is a need for ecologically fragile karst of Chongqing area of the key aspects of the comprehensive management of research.Its management skills and experience not only to solve the ecologically fragile areas of Chongqing environmental issues which play an important guiding role, but also in Sichuan,northeastern Guizhou,southern Sichuan,and Hunan,Hubei,the West area has a wide range of applicability and the promotion of the value.In this study,micro-runoff plots in Nanchuan of Chongqing city of the MuDu river basin for natural rainfall field observations,observation period from October 2007 to October 2008,the study of woodland and three arable land(5 degrees sloping land,Have governance land,10 degrees sloping land) the soil characteristics and its influencing factors,The main analysis of the rainfall factor,vegetation factor,terrain factor and human factor of soil erosion in the Karst region effect,results showed as follows:1.The study area for seven years,2002-2008 years rainfall analysis showed that: Rainfall between 100mm to 200mm of May,June,July and August,accounting for 58.2 percent of the total rainfall,rainfall in the study area are mainly distributed in May to August,this time of the flood season is in the region.Views from the rainfall,the rainfall in seven years are less than 25mm of rainfall-based(number of total rainfall of 75.8%).Seven three-level integrated rainfall data analysis,the rainfall which is less than 25mm accounted for 37.5%,the rainfall which between 25mm to 50mm accounted for 25.9%,the rainfall which is more than 50mm accounted for 36.6%of the rainfall.An inferior race,so the main study area rainfall which is more than 50mm and sub rainfall which is less than 25mm of rainfall-based.Rainfall duration(t<12h) accounted for 43.4 percent of the total number,more than 12～24h and 24h of 27.6% and 29.1%.Rainfall duration which is less than 12h,12～24h and 24h were 36.5%,30.4%and 33.1%,t<12h as the rainfall duration is the largest,24h rainfall followed.It is mainly long t<12h number of rainfall,while rainfall in less than 12h and more than 24h for the main source.Average rainfall intensity in accordance with sub-scale study,2002-2008 mainly to rainfall intensity which is more than 5mm/h mainly rainfall,total rainfall was accounted for 86.7% frequency,87.0%,89.8%,87.1%,91.4%,92.6%and 88.9%,88.9%an average of seven years;I₃₀ order of magnitude by 2002-2008 years I₃₀<10mm/h rainfall number,respectively,the total rainfall was accounted for 70.7% frequency,70.4%,76.3%,72.6%,74.1%,68.5%and 79.4%,73.2%an average of seven years;the number of rainfall mainly to heavy rain and storms;rainfall in heavy rain at the same time 41.1%,28.4%for the heavy rain,heavy rain for the 19.7,10.7%for the heavy rainfall;between eigenvalues in the rain,with the exception of erosive rainfall P and the maximum 30-minute rainfall intensity(I₃₀) the correlation between the non-significant,the other between the characteristic values are extremely significant level.2.Analysis the runoff of micro-runoff plots in this study,results showed as follows:Rainfall in the same conditions,the 4 categories of runoff showed a clear trend:Woodland＜Have governance land＜5 degrees sloping land＜10 degrees sloping land.This shows that the slope of cultivated land increased runoff increases.At the same time to have governance land and sloping land with similar runoff,with obvious differences in forest runoff, woodland runoff to a minimum.Study observation,because of the growth of lush crops,vegetation cover increased,strengthening the role of storing rainfall,soil and water conservation has played a certain role.Agricultural practices on soil tillage,fertilization,such as foot pressure and change of soil physical,chemical nature of the role of the impact of soil water and soil conservation,increased soil erosion of agricultural land.Erosion of arable land and rainfall runoff showed a significant correlation. Runoff have two essential conditions are sufficient to meet the volume of rainfall and the strength of the soil to erosion.R₃₀ is the rainfall erosivity and rainfall I₃₀ reflects the composite indicator,and the runoff has a significant or very significant correlation between the more accurate and reasonable projections runoff.3.Analysis the amount of soil erosion of micro-runoff plots in this study,results showed as follows:In the same rainfall conditions,the order of the sediment loss is: Woodland＜Have governance land＜5 degrees sloping land＜10 degrees sloping land. Sediment in the amount of rainfall when the trend was increasing steps;when small rainfall,10°slope farmland runoff and sediment yield obvious Have governance land no runoff and sediment yield,indicating that the greater the slope ahead of runoff,and sediment yield process.In this study,four types of land-use types,in addition to forest land,the other three land-use types of erosive rainfall,rainfall erosivity and runoff and sediment loss in both the performance of highly significant correlation.4.Analysis the soil moisture content of micro-runoff plots in this study,results showed as follows:In the same rainfall conditions,the order of soil moisture content is: 5 degrees sloping land＞Have governance land＞10 degrees sloping land＞woodland.Have governance land and 5 degrees sloping land and degrees sloping land are similar in Soil moisture content,have obvious differences in soil moisture content with woodland.At the same time,with increased rainfall,soil moisture slightly increasing trend.Low soil moisture,forest area as a result of soil compaction,soil water holding capacity of small,poor permeability.Farmland soil moisture high,the reason should be cultivated crops planted,due to the impact of farming and crop,soil porosity to increase,making loose porous soil,and enhance and maintain the infiltration of precipitation on soil properties and water storage capacity and precipitation into the soil in the scope of a more deep,at the same time zone as a result of soil compaction,soil water holding capacity of small,poor permeability,low soil moisture content,the relatively higher soil water content.With the increase in rainfall,soil water storage capacity around the type of increases shows that the study area is mainly runoff out of Maximum field capacity,that is saturated in the soil water storage capacity will be generated after the runoff.Of course,in heavy rain and heavy rain,the rain water into the soil could have a run-off on the will to Ultra runoff infiltration mainly.