Experiment Studies And Modeling Of Unsaturated Soil Solute Transport Under Middle Water Irrigation

Aimed at the problems resulting from the middle water irrigation, The soil water movement and solute transport(NH4-N, P) in the soil column under different irrigation frequencies quantities and so on are investigated in this study. Meantime, the mathematical model of water transport and the transformation of NH4-N, P in unsaturated soil are established and solved by the characteristic finite difference method. The research results will form a basis for long term prediction.1. The contamination distribution under the worst irrigation condition was discussed. Such as the effect of different irrigation ratio and rainstorm. From the experiment data we can get: Spread area of solute was the same as water movement. But, four kinds of irrigation frequency have various influence. Another phenomena should be considered, most of NH4-N, P can not moved deeply in soil but cumulate at upper layer of soil. That is to say, the adsorption of soil for NH4-N, P leads to the result that transportation of solute lags behind water movement. At the same time, the infiltration and leaching under rainfall play a more important role on contamination transformation than on water quantity. According to the analysis of laboratory experiments, except the cumulate of contamination in soil for a long time, the middle water irrigation willnot endanger deep embedding underground water if we take account of water saving irrigation methods.2. On the basis of key parameters that drawn from the test results, the mathematic modeling of water movement and NH4-N, P transportation was established. Programs were made to get the numerical solution by Matlab software. In general, The calculated results agree with the observed data. This model can simulate and forecast the solute transportation in a long run.