Soil Water And Salt Transport Experimental Study And Mathematical Modeling

Water flow and salt transfer in the unsaturated soil under one-dimensionwater ponding infiltration and drip irrigation are studied through thetheoretica1 analysis and simulated experiment method in accordance with thecharacteristics of alkali-saline soils and the concerning research resultsat home and abroad.A series of experiments of the soi1 water movement and salt transfer withthe different initia1 soi1 moisture content, irrigation duration and thewetting front depth are conducted under one-dimension water pondinginfiltration at lab. The characteristics of the infiltration, saltconcentration distribution, the influence of initial soil moisture contenton the soil water and salt transport processes and the relation between waterand salt transport are analyzed. The results indicate that the Kostiakov modelcan describe the cumulated infiltration well. The power function may be usedto describe the relationships among the wetting front distance, theinfiltration rate and the infiltration duration respectively. Moreover theexponential function may also be used to express the relationships among thesalt content, salt concentration, Na+, Cl concentration and the depth of thesoil profile. The depth of desaltification zone, the location of the peak ofthe salt content and the peak of the salt concentration increase with theincrement of the infiltration time. The power functions may describe therelations of the depth of the desaltification zone, the locations of the peakof the salt content and the peak of the salt concentration with theinfiltration duration repetitively. To the certain wetting depth, theincrease of initial soil moisture takes disadvantage of desaltification inalkali-saline soils. The relations of the cumulated infiltration with theconcerning parameters reflecting the soil salt transfer features are analyzedand the power function can describe the relations well. On the basis of theseanalysis results mentioned above, a simple model to describe one-dimensionunsaturated soil water movement processes based on the Darcy's law,Brook-Corey equation and the hypothesis that soil water flux is only functionof the infiltration time is developed. On the other hand, a new soil salttransfer model with single parameter or two parameters based on the convectionand diffusion theory of soil solute transfer and the hypothesis that averagerate concentration is kC or uCz l where k is a coefficient, u is a coefficientof concentration allocation, C is concentration and z is the depth of soilprofile, has a1so been estab1ished. The theoretica1 re1ationship is checkedout by the experimenta1 results of the one--dimension water pondiflginfiltration of the sa1t effected soil. The resu1ts show that the mode1 canref1ect the basic characters of the soil water and so1ute concentrationdistribution within the soi1 profi1e.In order to study the water and salt transfer features under the dripirrigat ion, a ser ies of experiment wi th di fferent emi tter rate, irrigat ion t imeand the initial soi1 moisture content are conducted at the 1ab. The maininf1uentia1 factors of the soi1 water and sa1t transfer, such as the drip rate,the cumu1ated infi1tration, the initial soil moisture, are ana1yzed based onthe experimenta1 resu1ts. The resu1ts indicate that the surface wateraccumu1ation range increases with the increment of the emitter rate and thecumulated infiltration. The re1ationships between x/z, ratio of thehorizonta1 distance and the vertica1 distance of the wetted vo1ume, and theinfiltration time can be described with the power function. There exist benot an obvious relation of x/z with the drip rate. The shape of the contourof the soi1 water content is similar to the shape of the wetted vo1ume. Thewater content near the drip emitter increases with the increment of the emitterrate, the cumu1ated infiltration and the initia1 soi1 moisture. With theincrease of the emitter rate and the init...