Agricultural sediment reduction using natural herbaceous buffer strips: a case study of the east African highland

Buffer strips are permanently vegetated areas situated immediately adjacent to streams and provide an efficient and economical way to reduce nutrient loads from agricultural areas, but no studies exist of their effectiveness from the East African highlands. We thus evaluated the sediment filtering capabilities of natural herbaceous buffer strips under tropical highland climatic conditions. Overland flow samples were collected at field edges and at various positions in herbaceous buffers and tested for total suspended sediment, nitrate-nitrogen and total phosphorus. There was a significant effect (P < 0.05) of distance from field edge on the mean values of nutrients. On average, a 10.0 m herbaceous buffer reduced the total phosphorus by 99%, total suspended sediment by 94% and nitrate-nitrogen by 85%. Altogether, the results suggest that herbaceous buffer strips are important to include in watershed management in agriculturally dominated tropical highlands in order to control sediment loss, stream siltation and the washout of nutrients.