|Ph.D Student||Levin Anna|
|Subject||Modeling Water Flow and Nitrogen Transformations in the|
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Abraham Shaviv|
|Mr. Peter Indelman (Deceased)|
|Full Thesis text|
The issue of water flow and solute transport with root water and nutrients uptake through the vadose zone represents a complex problem that requires adequate knowledge of a large spectrum of phenomena. Although many investigations have been dedicated to the better understanding of moisture and solute dynamics in the root zone, the problem is still insufficiently comprehended.
The flow problem has been solved numerically for a wide range of the soil-root conductivity ratio (SRCR). Two different types of root water uptake (RWU) mechanisms have been constructed and examined: one relates to low/moderate SRCR and exhibits a so-called “moving uptake front” effect observed in several experimental studies, whereas the other one is associated with large SRCR and is strongly dependent on root density.
A physically based analytical model has been suggested for plant roots of low/moderate SRCR. It was presumed that: (1) the flow is gravitational and (2) the soil moisture distribution within the root water activity zone is uniform. The solution of the mass balance equation in its integral form by the method of characteristics led to the two functional equations for soil and root pressure heads. The model represents a reasonable compromise between the complicated mechanism of unsaturated water flow with RWU and our insufficient knowledge of these processes. Besides its theoretical importance, the model yields the velocity field, thus, constituting a preliminary step toward the solution of contaminant transport problems.
Analytical solutions have been derived for two problems often encountered in agriculture: the movement of a fertilizer applied at the soil surface and the propagation of a chemical injected with the irrigation water. Explicit analytical expressions for the solute concentration have been obtained under assumptions of gravitational flow and advective solute transport. Percolation of a contaminant initially applied at the soil surface has been analyzed during ten infiltration-redistribution cycles.
A numerical model, which incorporates water flow and RWU, salt transport and osmotic effects, nitrogen transformations and its uptake, and root growth and development, has been developed and applied to analyze efficiency of different irrigation and fertilization scenarios. The calculated fertilization efficiency was closely related to the irrigation schedule. The differences in irrigation and fertilization efficiencies between systems of low/moderate and large SRCR were relatively small. In any case, thorough model calibration versus field and/or laboratory experiments is essential in order to provide more reliable assessment of irrigation and fertilization efficiency.