Effects Of Different Types Of Land Use On Soil Loss Tolerance In Karst

The area of karst region in China is 3,440,000km~2,which is about 1/3 of land area. Among that the bare karst mountainous region is about 90.7 km~2.Southwest China karst region where Guizhou Province is the core appears the problem of karst rocky desertification as one of four major ecological disasters which make the area become the most difficult remediation and getting rid of poverty area.It is because that very vulnerable and sensitive geological environment,dual pressures of over population and economic and social backwardness and eco-environmental degradation caused by historical reason.Soil erosion is the direct reason of rocky desertification,but in the karst region the research of it is more lag.The research is about the soil loss tolerance of different land use patterns that the concretely study is the soil quality difference caused by human activity,and lucubrate dissolution soil formation rate of different land use pattern.The research has important scientific significance and applied prospects on exploring the process of soil erosion,study on karst effect,the reasonable use and protection of soil resource in karst region,soil erosion control and rock-desertification governance and the economic development of the karst rural area.The research area of this paper locates in karst region of Zhongliang Mountain in Chongqing.The dissolution rate under different land-use which is obtained by the solution samples and acid-insoluble content of the strata in the research region canobtain the rate of soil formation.The soil loss tolerance of different land use patterns also can be obtained.This research evaluates the soil erosion hazard in karst region and probe the influence of soil formation rate of different land use pattern.The test pieces were made from the local formation of Jialingjiang ground dolomitic limestone rock samples whose diameter was 40mm and thickness was 3mm.The woodland,grassland,garden,vegetable and arable land,such as five kinds of land use patterns were selected.The test pieces were placed the laying of samples representative of its different parts(-5 cm,-20 cm,-50 cm).Each of the laying of land-use sets two samples within a hydrological year(November 22,2007 -2008 in November 23);At the same time,a set of test piece was put at the same place compared rates in the summer six months(March 22,2008 -2008 year September 25) with the whole year.When the test pieces were out,the rates was calculated.The research proves that the land-use pattern can obviously influence the properties of soil.In general,the soil physical property of woodland and grassland is better than other land use pattern.Land use pattern has a significant impact on soil organic matter, especially on surface soil.The soil organic matter of woodland and grassland is in a high level.Because of human activity such as tillage and fertilization,the discipline of Nitrogen,Phosphorus,Potassium and other nutrients is more complicated.The soil pH is overall low.The rate of soil formation is the foundation of erosion tolerance.It can also be used as soil loss tolerance.The result indicates that the soil loss tolerance amount scope is form 19.02 t/(km~2.a) to 49.01t/(km~2.a).It is significantly less than the existing state standards 500 t/(km~2.a).In the different land use patterns,the difference of the soil loss tolerance is distinct in karst area.The soil loss tolerance of forest land is 32.72-49.01 t/(km~2.a);grassland is 25.57～39.27 t/(km~2.a);vegetable land is 27.09～35.01 t / (km~2.a);arable land is 19.02～27.85t /(km~2.a),Garden land is 19.33～25.11 t/(km~2.a).The mean soil loss tolerance ordinal of forest land,grassland,vegetable land, arable land and garden land one by one is 37.34 t/(km~2.a),33.46 t/(km~2.a),30.77 t/(km~2.a),23.08t/(km~2.a),22.49 t/(km~2.a).The results showed that different land use patterns have obvious influence on dissolution rate.Contrast the average dissolution rate of different land use patterns in rainy season,the result is forest land(303.92mg/m~2·d)＞grassland (256.29mg/m~2·d)＞vegetable land(210.55 mg/m~2·d)＞arable land(174.83 mg/m~2·d)＞garden land(125.95 mg/m~2·d).Contrast the average dissolution rate of different land use patterns in the whole year,the result is forest land＞grassland＞vegetable land＞arable land＞garden land.The largest one is forest land whose average dissolution rate is 232.50mg/m~2·d.Secondly for is grassland(208.33 mg/m~2·d) and vegetable land(190.80mg/m~2·d).Then arable land and garden land are with a relatively lower,respectively,38.18%and 41.17%.With compared the dissolution rate of rainy season and the whole year in different land use patterns,it is found that the dissolution rates at -50cm of forest land,vegetable land and arable land in rainy season are less than the dissolution rates in the whole year and the rest one are more than it.From the proportion of dissolution quantity in rainy season on it in the whole year,it is found that at -50cm of forest land,vegetable land and arable land in rainy season that are less than 50%and the rest ones are more than 50%.The average proportion of dissolution quantity in rainy season on it in the whole year one by one is forest land (64.57%)＞grassland(63.83%)＞arable land(56.55%)＞vegetable land(54.91%)＞garden land(52.10%).With compared the dissolution rate of rainy season and the whole year, it found that temperature and rainfall are the important factors in the dissolution process and the dissolution contribution rate of rainy season is bigger.Land use pattern will influence dissolution rate by influence soil physicochemical property.Karst action is jointly influenced by the reciprocity of soil pH,organic carbon,soil moisture content and extent of porosity,and the underground karst dissolution is the comprehensive function of multi-factor and reciprocity of them.Relative to other regions,the absolute amount of erosion was less.But because of its special geological background,the rate of soil formation is slow;the soil loss tolerance is small.From the contrast of soil loss tolerance and soil erosion intensity,the soil erosion in karst region is very serious.And there are two basic ways to hold the existing soil resources.One is preserving the situ and coverage rate of soil and increasing the anti-erosion ability of soil,the other is raising the soil formation rate in karst region. Slope farmland has less soil loss tolerance,stronger interference of human activities, more intense tillage erosion and weaker anti-erosion ability than the other land use patterns,so it appears soil erosion more easily.The erosion intensity in the research area is 99-145 times of its soil loss tolerance and 119.8 times of its average soil loss tolerance.With the increased soil erosion,the nutrient loss and negative growth of soil layer,large acreage of rock is bared and slope farmland will become the first area where appears soil erosion.Therefore,the prevention of soil erosion in kasrt region slope farmland is very important.The dissolution rate of forest land is the largest and can promote the dissolution and soil formation rate of carbonate rock.And forest land soil properties and corrosion resistance are better and it is propitious to continuously thickening soil layer in karst region.Increasing forest coverage rate of karst region has major significance.