Comparative Studies Of Soil Micromorphological Characters On Different Land Use Type At Long-term Sewage Irrigation Area In Xi'an Suburb

Soil environment problems and land use types are induced by Long-term city wastewater irrigating crops, which has a great influence on soil quality. It has exercised most attraction on researchers. This paper dissects and investigates typical vegetable cultivation (LXH) and farm land (XCZ) in the northern suburb of Xi'an sewage irrigation, makes comparisons in soil micromorphological types under those two land use types according to physical-chemical property of soil, explores the land use types, how city wastewater influence soil micromorphology, and inherent law between them, in order to provide evidence for soil changes and improve soil ecological functions.By detailed field investigation, this paper chooses the vegetable cultivation (LXH) and farm land (XCZ) as research objects. Then the paper makes thin sections and uses the Leica—DMRX polarizing microscope to observe, analyze and describe the soil micromorphological types, features, and spatial distribution (including coarse grains characteristics, mineral composition and forms, voids characteristics, microstructure, soil formation, soil fabric etc.). High resolution digital images abouttypical micromorphology are collected. Using SISC IAS V8.0 optical image analysis softwareanalyzes and measures soil micromorphological characteristics (including the length of the coarsegrains, width, elongation, roundness, perimeter, area, equal diameter, orientation and roughness, the content and morphology of soil formation, the absolute size and quantity of pore, etc.). The physical and chemical characteristics of soil (such as pH values, magnetic susceptibility and grain size, CaCO₃, TOC, moisture, bulk density, etc) are measured and analyzed. On the basis of experimental results, some conclusions are drawn as follows:(1)The quality and size of digital image has a marked influence on quantitative results. Digital images of different magnifying multiple have great infection on numerical value analysis. The most suitable multiple to Sise IASV8.0 digital image processing system is 10x10 multiples image by multiple tests. Normalization method can settle the problem of data dispersion degree when analyzing the data.(2) The minerals assemblage is similar at vegetable cultivation and farm land. The results were as follows: the minerals composition of coarse grains in different horizons is very similar, which is mainly composed of Quartz and Plagioclase, and is occasionally composed of Hornblende, Mica, Epidote, Opacite and so on. However, there are obvious differences in C/F_10μm ratio, mineral content, and coarse features. Vegetable cultivation has more large particles. It makes coarse change round because of human disturbance, but due to the broken coarse level, the psephicity of coarse grains become larger and coarse angular change significantly at the section. The C/F_10μm values are larger, the value variety range is smaller, which is between 0.45 and 0.51, but the maximum appears in the Ap2 horizon. The amount of coarse grains in farmland is obviously less than vegetables; the grain is also smaller. The C/F_10μm value is smaller, however the changing range is greater, which is between 0.16 and 0.43, and the maximum appears in the Ap1 horizon. Coarse grains various parameters change little difference in two profiles.(3) The pedological features are similar in profile vegetable cultivation soil and farm land soil, both of them are mainly composed of calcite, amorphous Fe-Mn and clay. The color of clay varies from brown yellow to yellow brown because it is mostly interfused by amorphous Fe-Mn. Besides residual clay, there is also abundant illuvial clay in profile LXH. Profile XCZ has more disseminated residual clay and less illuvial clay. Amorphous Fe-Mn contamination mainly blends with clay. The distributions of secondary-calcite characteristics are similar in two sections, which are mainly cryptocrystal calcite and microlite calcite, and most of them appearing in base material. Secondary-calcite mainly shows the types of fillings, coating, sub-coating and rod-shape inserts in both profiles, only have some differences in abundances and shape.(4)There are the coexistence of small regular pores and bulky, irregular pores in Ap horizon. The pores in profile vegetables are more regular and smooth comparatively, while in profile cultivation the pores have more rough void walls. On the growth degree of the porosity, the LXH section is also higher than the degree of XCZ section hole growth, which the former hole is bulky and lacunose (17.45～21.77%). The XCZ section soil porosity is smaller (9.96～15.47% ). The B horizons in both profiles are characterized by the presence of a large amount of small irregular voids with rough voidwalls.