Optimum Soil Bund Spacing: Cost–Benefit Analysis in a Midland Agro-Ecological Region of Ethiopia

In the highlands of Ethiopia, soil erosion by water is a key threat to ecosystem services and food security. Soon after the 1973/1974 drought, soil bund technology was implemented in various parts of Ethiopia, but the adoption rate among farmers remains poor, mainly due to a lack of information on the benefits and costs of different bund spacing. Here, in the midland agro-ecological region of Ethiopia, we examined the environmental, economic, and social impacts of soil bund spacing by conducting field explement, cost–benefit analyses, and key informant interviews. To conduct the field experiment, runoff plots (each 3 × 30 m) were constructed in farmland and installed with 0 (control) to 4 soil bunds. Runoff and soil loss parameters and teff ( Eragrostis tef [Zucc.] Trotter) were then determined for each plot. Runoff and soil loss were highest in the control plot, whereas crop yield (kg m −2 ) was highest in plots with bunds. As the number of bunds was increased, which decreased the effective slope size, soil and runoff loss decreased but arable land loss and bund construction and maintenance costs increased. All the bund spacing, including control, were found to have a positive net present value under several scenarios; however, different values were obtained depending on the spacing. Taking the entire set of economic, environmental, and social factors into consideration, 2 bunds spaced 12.7-m apart per 30-m plot was considered optimal for the study plots. Utilization of this bund spacing maximized the environmental and social benefits and minimized economic costs.