The effect of physical and chemical treatments on runoff, infiltration and soil loss

In recent years, intensive drought has caused a severe yield reduction in rain-fed trees. Increasing runoff of low amount rainfall can be used to provide partial water requirement of rain-fed trees. To achieve this objective, some strategies including gravel removal (G), rill construction across to slope (R) and applying of baking soda (S) and their effects on runoff, rainfall infiltration and soil loss were simulated by a laboratory rainfall simulator under 33 mm h-1 intensity in 60 minutes. The results showed that the combination of R, G- and S significantly increase the soil loss, runoff, and runoff coefficient 14.43, 2.74 and 1.59 and decrease rainfall threshold and infiltration 2.1 and 1.57 times compared to the control, respectively. Separately, S, R and G- were the most effective in the runoff enhancement (31.2, 29.3 and 22%) and in infiltration reduction (8.4, 7 and 5%), respectively. S had the most effect on soil loss due to dispersion of soil surface. Furthermore, the effect of R was more visible than G- in increasing the soil loss. Applying sodium bicarbonate (S) increased the sodium in runoff and sediment, but there were no salinity (EC= 0.51-0.60 dS m-1) and sodicity (SAR= 0.34-0.73) hazard in runoff. In saturated extract of sediment, the salinity (EC= 1.75-2.23 dS m-1) and sodium (SAR= 1.96-3.45) hazard were relatively high and low, respectively. Although, chemical treatments (S) did not show the sodicity hazard very much, the use of S must be considered carefully.