HYDROLOGIC AND SEDIMENTOLOGIC BEHAVIOR OF A CONSERVATION BENCH TERRACE SYSTEM IN A SUB–HUMID CLIMATE

摘要

The performance of a Conservation Bench Terrace (CBT) system for controlling runoff and soil erosion and improving crop productivity in comparison to the conventional system of farming on sloping borders (i.e., making plots on slopes at 2% to 4%) has been studied in a sub-humid climate. The CBT system has been found effective in reducing runoff and soil loss by over 80% and 90%, respectively, compared to the conventional system. On an average (1987-1994), the CBT system registered 7.4% of rainfall as runoff and 1.19 Mg/ha of soil loss as compared to 36.3% and 10.1 Mg/ha in the conventional system of sloping borders. The analysis of storm events on a daily basis during the study period revealed that storms greater than 100 mm, though only 7.7% of the total number of storms, were responsible for highest average annual runoff and soil loss in sloping borders compared to other storm sizes, while a major portion of average annual runoff and soil loss in the CBT system was caused by this storm size category. Among the linear, quadratic, and power functions, the quadratic relationship best fit the overall runoff and soil loss data covering all storm sizes during the study period. However, in the case of storm category-wise analysis of rainfall versus runoff, the linear model gave the best fit to the observed data, while for the rainfall-soil loss relationship, the quadratic function fitted the data best for the individual storm size categories. The values of curve number in the SCS method have been optimized for the conventional and CBT systems using the observed rainfall-runoff data to better predict the runoff instead of using the standard values. The support practice factor (P) in the USLE for the CBT system has been computed as 0.09, which is comparable to the reported value of 0.10 for bench terracing. Apart from reducing runoff and soil loss, the CBT system was effective in improving the productivity by over 19% in terms of maize-equivalent yields as compared to the conventional system