Effects of Soil Preparation for Laboratorial Erosion Studies on Surface Runoff

Despite of soil disturbance, transfer to the laboratory and preparation inside the plots which themselves lead to lower validity of the results, the experimental study on runoff and erosion at plot scale with many research advantages are inevitable. However, there has been less attention to evaluate the effects of soil preparation on runoff and sediment variables. The present study was therefore conducted to compare surface runoff in two undisturbed (natural) and disturbed (during various steps of preparing soil for laboratorial studies) soil conditions. To achieve the study purposes, 1×1 m-plots were considered in a slope with sandy-clay-loam soil and gradient of 18% under simulated rainfall with three intensities of 40, 60 and 80 mm h-1. The study slope was located in the vicinity of Kodir village in upper Educational and Research Forest Watershed of Tarbiat Modares University. The time-to-runoff in the output of each plot was recorded and the runoff volume and coefficient at five three-minute intervals was subsequently measured. The results showed that the average time-to-runoff, runoff volume and coefficient were significantly (p≤0.01) increased 2.29, 3.45 and 2.79 times, respectively due to the soil disturbance which clearly indicated the impossibility generalization of laboratorial runoff and erosion results to natural conditions without considering the effects of soil disturbance. The results showed the synergistic interaction of soil disturbance and rainfall intensity on time-to-runoff and antagonistic interaction on runoff volume and coefficient.