The Study Of The Distribution Of Soil Properties In Soil Profiles And Microtopography Originated From Purple Sandstone And Mudstone

The purple soil distributing mostly in hilly and low mountainous region of Sichuan basin. The acreage of purple soil in this area is about 0.16 million km2, which is about 28% of Sichuan province and Chongqing city, and the largest parent materials are J2s and J3p. The purple soil is lithology soil and the main weathering effect is physical weathering. The purple soil is shallow, generally, the soil on the sloping field especially the soil in the slope top is eroded to midslope and basal slope by the rainwater before the end of soil development. This thesis use the points of soil development, distributing and migratory rules of soil elements and ecological environment, with the system of parent materials-soil-ecological environment and the object of mudstone and sandstone which belong to the parent material of J2s in hilly region in Chongqing. And on this foundation, this thesis analyze difference of the distributing rules of soil properties,element migratory, the degree of soil profile development and soil degradation in different microtopography between two different soils, and the main results are as follows:(1)The distributing rules of soil elements in soil profiles and microtopographyFirst, using the statistical method we can found that soil pH, total N,total P, total K, alkaline hydrolytic nitrogen, available P, available K in the soil which develop from purple mudstone is higher than sandstone soil.In these two type soil, there are no obvious otherness about the content of organic matter and cation exchange capacity (CEC). From slope top to basal slope, the soil pH of mudstone soil is decreasing gradually(in slope top is 7.5±0.3,in midslope is 7.0±0.46, in basal slope is 6.6±1.05), this prove that the process of soil acidification is more and more strong, but in sandstone soil the rules of soil pH is completely opposite. The distributing rules of organic matter is the same (basal slope>slope top>midslope), as well as the total N, available Zn, total Fe and total Mn. But there are difference of distributing rules in different microtopography on total P, available P, alkaline hydrolytic nitrogen, total K, available K and microelements. We can found that the variance of the content of soil pH, total P, total K, available P, CEC, total Zn and total Cu in these two type soil is observable. For example, the variance of soil pH between purple mudstone and sandstone soil is highly significant in the soil profile A and C of the slope top, in the soil profile A and B of the midslope the variance is significant; The variance of total P in the profile A of the slope top is highly significant. In addition, the distribution of soil pH, alkaline hydrolytic nitrogen, total P, available P, total K and available K in microtopography is different. For alkaline hydrolytic nitrogen example, from slope top to basal slope, the content of alkaline hydrolytic nitrogen gradually increase in mudstone soil,but in sandstone soil,the content of hydrolytic nitrogen is basal slope>slope top>midslope.Secondly, with the correlation analysis for soil pH, organic matter, CEC, major elements and microelements, we can found that there are highly significant positive correlation between alkaline hydrolytic nitrogen, available P and available K, this indicated that there are stimulative effective role between them, as well as between alkaline hydrolytic nitrogen, available P and available K, total N and organic matter(in purple mudstone soil the correlation coefficient is respectively r1=0.87**,r2=0.531**,r3=0.552**,r4=0.771**,n=48; and in purple sandstone soil the correlation coefficient is respectively r1=0.776**,r2=0.646**,r3=0.536**,r4=0.787**,n=67).In the soil developed from purple mudstone material, soil pH and total P showed highly significant positive correlation (r=0.385**,n=48), but highly significant negative correlation between pH and available P, CEC (ri=-0.512**,r2=-0.397**,n=48). On the other hand, in the soil developed purple sandstone material, between soil pH and organic matter, alkaline hydrolytic nitrogen, available P showed highly significant negative correlation(ri=-0.465**,r2=-0.502**,r3=-0.527**,n=67), significant negative correlation between soil pH and total N(r=-0.269**,n=67), and no significant correlation between soil pH and total P and CEC. The soil CEC just with soil pH showed highly significant negative correlation in purple mudstone soil, but in purple sandstone soil there are no significant correlation between CEC and soil pH, whereas, it showed significant negative correlation between CEC and organic matter, significant positive correlation between CEC and total P and total K. We can educed some linear equations with protracting scatter diagram. For example, the equation of organic matter and total N is YTN=0.042xo M+0.263,R2=0.594, and in purple sandstone soil is YT N=0.043xOM+0.184,R2=0.619. In the soil whether developed from purple mudstone or sandstone, the major elements, organic matter and CEC have effective action to the available microelements, but not significant to total content of microelements. In the purple sandstone soil, the soil pH, total P, total K, available K and CEC have significant effect to the total content of microelements.(2) The migratory rules of soil elements in soil profilesWith statistical analysis of the element migratory coefficient we can make clear that the elements N, Cu, Zn, Mn and Pb migratory in opposite direction in profile A of the slope top, the major development process in the purple mudstone soil is leaching process, but in purple sandstone soil is enrichment process. Other elements which migratory in opposite direction are the Zn in profile A of basal slope, the Cu, Zn and Mn in profile B of midslope and the Pb in profile A of basal slope. This may be related to soil water characteristics, soil texture and fertilization measures. The migratory intensity of major elements is higher than microelements, and the migratory intensity of soil N is higher than soil P and K. And there are different element migratory intensity especially soil N, P and K between purple mudstone soil and sandstone soil, as well as in different microtopography, this indicated that the strength of soil development is different with different microtopography and parent material.(3) soil degradation index in microtopographyMaking the soil in the slope top as control, the soil degradation index in midslope and basal slope are positive number, this showed that the strength of soil degradation in midslope and basal slope is lower than slope top. The soil degradation index in midslope of purple sandstone soil is higher than mudstone soil, but lower in basal slope, this showed mudstone soil in basal slope its nutritional elements strongly deposited, while in midslope its leaching process and illuviation almost the same with slope top.