Optimal spacing of soil conservation barriers: Example of rock bunds in Burkina Faso

A mathematical model is presented for computing the economically optimal spacing of conservation barriers or bunds. Crop yield is generally greatest immediately upslope of bunds. However, labor and availability of rocks or other materials limits the practicality of narrow bund spacings. The authors assumed a quadratic response of yield to distance from the bund and used sorghum yield data from test fields on a 1% slope to develop model coefficients. Three labor scenarios were investigated: local citizens working together on a community land management project (maximum construction cost), a farm family assisted by an NGO to transport rocks, and a farm family with a nearby supply of rocks and their own tools (minimum construction cost). For the various scenarios studied, optimum bund spacing was determined to be 23-40 m. The authors state that the method could be used for spacing terraces, windbreaks, or other types of conservation barriers. Further research should include incorporating risk, environmental aspects, rock bund age, as well as interactions with fertilizer and other inputs.