تجزیه و تحلیل از انتقال مواد شیمیایی محلول توسط آب رواناب در حوزه

In order to determine the main factors influencing soluble chemical transfer and corresponding techniques for reducing fertilizer loss caused by runoff in irrigated fields, a physically based two-layer model was developed with incomplete mixing theory. Different forms of incomplete mixing parameters were introduced in the model, which was successfully verified with previous published experimental data. According to comparison, the chemicals loss of fertilizer is very sensitive to the runoff-related parameter while it is not sensitive to the infiltration-related parameter. The calculated results show that the chemicals in infiltration water play an important role in the early time of rainfall even with saturated soil, and it is mainly in the runoff flow in the late rainfall. Therefore, prevention of shallow subsurface drainage in the early rainfall is an effective way to reduce fertilizer loss, and the coverage on soil surface is another effective way.

Fertilizers applied in fields are frequently transported into surface water body by rainfall or irrigation induced overland flow, consequently resulting in a significant impact on the water quality, which is also an economic loss and have become a matter of considerable concern [1-17]. Determining the accurate amount of soil chemicals of fertilizers transfer into runoff and reducing fertilizer loss are essential for the agricultural management of non-point source pollution. The conventional mixing zone theory assumes that there exists a region below the soil surface in which surface water, soil solution, and infiltrating water mix completely and instantaneously and thatthere is no chemical transfer into that region from the soil below (see Fig.1). Fig.1 Sketch of simple two-layer model In early efforts of past 30 years, it was generally assumed that, at any moment in time, a certain thin zone of surface soil (hereafter called the mixing layer) and soil water mix completely and instantaneously with rainwater[10,18], and the mixing layer depth is constant. Ahuja et al.[2] showed that the degree of interaction between rain water and soil water decreases exponentially with the depth, so they presented the concept of Effective Depth ofInteraction (EDI), within which the degree of mixing is uniform and equals that of the soil surface. Ahuja and Lehman[4] and Zhang et al.[16] showed that the observed mixing-layer depth is much shallower than the depth required to fit mixing-layer models to experimental data. Snyder and Woolhiser[19] also concluded that the complete mixing model might only be appropriate as the infiltration rate is high. Therefore, some scholars[4,13] modeled the chemical transport from soil to runoff with incomplete or non-uniform mixing theory. Based on the conservation law for the EDI, Wang et al.[20,21] established a soil chemical-runoff interaction model and further developed a new incomplete nonuniform mixing theory. Much attention has been paid to the theory and modeling of fertilizer contaminant transport in saturated soil, and most studies were started from the initiation of ponding-runoff [4, 11-15]. In fact, a certain ponding water is needed to produce runoff [17,18, 22]. In addition, the majority of the current models often took the incomplete mixing parameters as constants rather than variable ones throughout a rainfall event, which could not give suggestions for reducing chemicals loss of fertilizer in detail. In this article, a simple two-layer model for soluble chemical transfer of fertilizer in runoff water is presented with incomplete mixing theory in unsaturated soil. The ponding mixing layer of pre-runoff process is also considered with simulated rainfall. The model is verified with previously published experimental data. In order to investigate the values of the incomplete mixing parameters and find ways to reduce chemical loss of fertilizer, different forms of incomplete mixing parameters are introduced. The differences between experimental data previously published and calculated data are analyzed and compared to determine the best fitted parameters, and they could provide reference for the control of soluble chemical loss of fertilizer in fields under the condition of irrigation and drainage.

A physically based simple two-layer analytical model has been developed, which could describe soluble chemical loss of fertilizer in runoff water from the rainfall initiation with special incomplete mixing theory. Based on chemicals conservation laws and water balance equations, different forms of incomplete mixing parameters for the model are successfully verified with previous published experiment. F for different forms of incomplete mixing parameters are involved, and the power function forms of both incomplete mixing parameters of