Theory And Application Research Of Determining Parameters Of Solute Transport In Soils

World population is increasing and land resource is reducing and degenerating continuously, thus man must enhance soil productive capacity, improve and utilize saline-alkali soil in order to increase staple food supply. More pesticide and chemical fertilizer in agriculture are used and more waste water and other waste materials in industry are unreasonably poured than before, thus soil and groundwater are polluted seriously, and then eco-environment and human health are threatened directly. So it is a world-focused question how to improve and utilize saline-alkali soil and how to lessen soil and water pollution caused by agriculture and industry production as well as life garbage. Those issues have advantageously-promoted the research of solute transport in soils. At present, with the development of computer technology, it is possible to establish model and prediction of a variety of actual production and life problems by using theory and method of solute transport. The key to establish model and predict lies in the determination of model parameters, which include generally dispersion coefficient and retardation factor.Based on semi-infinite convection-dispersion transport equation, the condition of solution is established. The analytical solution of solute concentration in an instantaneous condition is developed by using Laplace transformation. In column tracer (SO42~) experiments, both spatial and temporal distributions of solute concentrations in three soils (red soil, paddy soil, and fluvo-aquic soil) are measured respectively by EDTA method. Compared fitted breakthrough curve (ETC) by program CXTFITwith observed BCT, two curves each has an obvious slope, in which maximum difference between observed value and fitted value of solute concentrations has arisen. Red soil needs the shortest times when breaking through the column. Retardation factors (R) estimated by program CXTFIT, slope method, and graphic method are very approximate, which indicates three methods are unanimous in determining R. R<\ in red soil shows that SO42- are desorbed; R>1 in paddy soil and fluvo-aquic soil shows that SO42- are absorbed. Dispersion coefficient (D0) estimated by slope method is close to fitted Z)0 when Brenner number is smaller, but there is the same conclusion only in mid-former section when Brenner number is larger. Graphic method is a new way determining hydrodynamic parameters. D() value estimated by graphic method have a larger difference in dcldt~t relation curve and t3/2dc/dt-~t relation curve. Only when using times corresponding with identical concentration slope in the middle of rise part and fall part, graphic method can obtain the close results with other methods and have a better effect on soils in which infiltration velocity is small than other method. Dispersion coefficient of red soil is about ten times as paddy soil and fluvo-aquic soil.It must utilize observed experimental data when three methods estimate hydrodynamic parameters. So researchers can raise the accuracy of parameters by increasing observed data in larger slope of BTC and using precision instruments and then lessening chemical error.