Study On Physical And Chemical Properties In Karst Area Of Chongqing

The natural geographical environment in karst area is a special geographical complex,The soil development of the ecological system in the vulnerable karst area has its own special characteristics.Under the background of Karst,The physical,chemical properties and structural composition of the soil will change with the change of different karst environment factors,which is different from the non karst area.In this paper,nanchuan town of Nanping in Chongqing kart area was taken taking as the study area, On the basis of previous studies several geographical environmental factors suche as the different slope,slope direction,different rocky desertification grade, different land use types, and so on,was selected. The effects of different geographical environment factors on the characteristics of soil physical and chemical properties were studied based on laboratory analysis in karst area of Chongqing province on the small scale.The conclusions are as following:1.Different slope have significant effects on soil physical and chemical properties.Through analyzing of soil physical and chemical properties of cultivated land in three kinds of slope（5-8°,8-15°,15-25°）,it indicates that soil clay content was decreased with the increase of slope range. In the range of less than 15 degree,with the increase of slope gradient, the proportion of water infiltration decreased, but there is no significant law of water content when the slope degree is more than 15 degree.Preliminary experimental results shows that in the range of less than 15 degree of cultivated land, there is a significant linear correlation between the soil aggregate destruction rate and the fractal dimension of water stable aggregates, which means the higher rate of aggregate destruction, the greater the fractal dimension of water stable aggregates, the worse the aggregate structure.The distribution characteristics of soil nutrients in different slope ranges are different.The distribution of alkaline nitrogen and available P follow in surface accumulation in the range of three kinds of slope.But with the increase of the slope,the distribution of available K and available P for the rules are inconsistent with non-karst areas.The soil physical and chemical properties of different slope have some differences. The difference of the soil mechanical composition between the reverse slope and the bedding slope is small. The soil bulk density, water content and porosity with the change of the slope position are consistent with the non karst area. The overall trend of the change in the 0-60 cm profile is gentle.The proportion of water stable aggregates in different slope positions is showed that the reverse slope is higher than that in the bedding slope.The rate of destruction aggregate and the fractal dimension of aggregate are lower than that of the bedding slope.It shows that reverse slope of the aggregate structure is better than the bedding slope,and the soil erosion and water storage property is better.The distribution of soil nutrients for bedding slope are consistent with the non karst area.But The distribution of soil nutrients for reverse slope in different slope position and depth of the section is great difference.It is breaking the law of soil nutrients down together with the decrease slope position.2. Research results shows that with the evolution of rocky desertification, the soil physical properties are strong response, And the cluster index of soil water stability group and the soil water content were the most prominent. With the increase of the degree of rocky desertification, the soil is more heavy and tight. And with the aggravation of rocky desertification degree, soil degradation rate slowed down.3.On the basis of ¹³⁷Cs nuclear tracer,studying the performance characteristic on two Karst depression and six Karst fissure soil leakage area of Nanchuan town of Nanping karst area.The results shows that the phenomenon of soil leakage in karst area is not everywhere.Due to the influence of rock structure joint system,soil leakage mainly occurs in the structure of the rock vertical joint.comparing the Soil nutrient distribution in sampling sites and characteristics of soil particle composition,and comparing them with ¹³⁷Cs in the aspect of activity correlation at the same time. It shows that there is a significant difference in the soil nutrients and the composition of the particles in the distribution of the section which is in the soil leakage and no loss of soil.4.Analysing the differences of soil physical properties of the 5 types of land use in karst area and non karst area.Through laboratory analysis experiment,it is showed that the clay content of five land use in karast area of Nanping Nanchuan is higher than that of the none karast area of Jinyun mountain. In addition to woodland and grassland, The soil bulk density of the Jinyun Mountain is higher than that of Nanchuan town of Nanping, the water content of the Jinyun Mountain is lower than that in the Nanchuan town of Nanping.Analysis shows that vegetation cover significantly affected aggregate stability.The aggregate destruction rate of 5 types of land use in the two areas was increased with the increase of the soil depth and the aggregate destruction rate of the bush and the forest land is the lowest.The non water stable aggregates volume fractal dimension is low and aggregation structure is high in the shrub, while that in the abandoned land and farmland are opposite.