Soil and Nutrient Losses under Cultivated Bush andClimbing Beans on Terraced Humid Highland Slopesof Southwestern Uganda

摘要

Highland regions characterized with terraced slopes in East Africa are faced with serious soil and nutrient losses that have affected agricultural productivity. However, limited studies have analysed the soil and nutrient losses on terraced slopes of these humid highland regions. Therefore, this study was conducted to assess the effects of climbing beans over the traditional bush beans' cultivation on soil erosion control in Bufundi sub catchment, Kabale District, South-western Uganda. Runoff trap approach was employed to assess erosion and the sites were characterized for soil physico-chemical properties. Terraced slopes planted with climbing beans showed significantly lower (P<0.05) annual runoff and soil loss of 36 m3 ha-1yr-1 and 121 kg ha-1 yr-1 over bush beans, 248 m3 ha-1yr-1 and 548 kg ha-1yr-1, respectively. Annual soil nitrogen, phosphorus and potassium losses were significantly higher from bush beans (1.87 kg N ha-1 yr-1; 0.6 kg P ha-1 yr-1 and 0.12 kg K ha-1 yr-1) over climbing beans (0.49 kg N ha-1 yr-1; 0.1 kg P ha-1 yr-1; and 0.03 kg K ha-1 yr-1). The total economic value of bush beans due to erosion was higher (75424 Ug shillings/ha) than that of climbing beans (15597 Ug shillings/ha). Generally, runoff, soil and nutrient losses were very low from both bean types. However, climbing beans were superior to bush beans in controlling runoff, soil and nutrient losses confirming their effectiveness in controlling erosion down the catchment.