Soil and water conservation (SWC) interventions are needed to control rainfall-driven erosion, and profitability of SWC measures at the sub-catchment scale emerges as the principal reason for their adoption. This study carried out a cost–benefit analysis of SWC measures in mountainous agricultural catchments. Physical data were obtained through field measurements of discharge, sediment and nutrient loss at the sub-catchment scale with and without SWC measures. The major cost benefits of various measures implemented in the study area were quantified using net present value (NPV), and direct market prices were employed in valuing the cost of items required for crop production. The results revealed that sediment loss decreased by 8.78 Mg ha−1 y−1 (46.8%) due to SWC measures, and the cost of production inputs, such as fertilizer (urea) and lime, was reduced by $17.97 ha−1 y−1 and $3.63 ha−1 y−1, respectively. Furthermore, crop yield was enhanced by 13% for teff, 19.4% for sorghum and 19.42% for chickpeas, which is equivalent to economic returns of $102, $96.9 and $140.25 ha−1 y−1, respectively. The total discounted cost of SWC interventions was about $331.74. This includes establishment costs, maintenance costs, input costs and the costs resulting from lost productive land. In sum, the total discounted benefits of SWC measures were the enhancement of crop production, a reduction in lime requirement and a reduction in the loss of total nitrogen and sediment, estimated at about $809.42. Hence, it is possible to deduce that SWC measures reduced nutrient depletion and greatly improved crop yield with a NPV of $477.68 ha−1. The results strongly suggest that SWC measures in the study sub-catchment, as well as in nearby areas with a similar indigenous SWC adoption strategy, topographic conditions and agroclimatic characteristics, should be maintained.
Soil Fertility and Crop Yield Variability under Major Soil and Water Conservation Technologies in the Usambara Mountains, Tanzania