A mathematical model was developed to simulate the application efficiency and uniformity of water-soluble fertilizers through furrow irrigation. The model simulates solute mass balance and transport for one-dimensional unsteady flow during the advance and post-advance phases of a furrow irrigation event. The model was programmed to determine the best timing and duration of fertilizer injection using two performance indices: solute application efficiency and solute application uniformity. The results from the model were compared with two sets of field data and were found to be in close agreement in terms of advance trajectories and surface water solute concentrations. Nearly 50,000 simulations were performed with the model and the results were analyzed in terms of best injection start and end times for fertilizer application efficiency and uniformity. It was found that the best injection duration time was from 5 to 15% of the time of cutoff for a complete irrigation. Most of the cases showed that the injection should take place in a relatively short time span, and at a relatively high injection rate.
An evaluation of the interactions between vegetation, overland and soil erosion can provide valuable insight for the conservation of soil and water. An experiment was conducted to study water infiltration, runoff generation process, rate of sediment erosion, and hydrodynamic characteristics of overland flow from a sloping hillside with different draw-off discharges from alfalfa and control plots with 20°slope. The effect of alfalfa on runoff and sediment transport reduction was quantitatively analyzed. Alfalfa was discussed for its ability to reduce the overland flow scouring force or change the runoff movement. Compared to the bare-soil plots, alfalfa plots generated a 1.77 times increase in infiltration rate. Furthermore, the down-slope water infiltration rate for the bare soil plots was higher than in the up-slope, while the opposite was found in the alfalfa plots. In addition, alfalfa had a significant effect on runoff and sediment yield. In comparison to the control, the runoff coefficient and sediment transportation rate decreased by 28.3% and 78.4% in the grass slope, respectively. The runoff generated from the alfalfa and bare-soil plots had similar trends with an initial increase and subsequent leveling to a steady-state rate. The transport of sediment reduced with time as a consequence of the depletion of loose surface materials. The maximum sediment concentration was recorded within the first few minutes of each event. The alfalfa plots had subcritical flow while the baresoil plots had supercritical flow, which indicate that the capability of the alfalfa slope for resisting soil erosion and sediment movement was greater than for bare soil plots. Moreover, the flow resistance coefficient and roughness coefficient for the alfalfa plots were both higher than for the bare-soil plots, which indicate that overland flow in alfalfa plots had retarded and was blocked, and the flow energy along the runoff path had gradually dissipated. Finally, the ability to erode and transport sediment had decreased.
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