Effects of Soil and Water Conservation Techniques on Soil Productivity and Bean Grain Yield in Nyamasheke District, Rwanda
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Erosion due to water runoff is one of the major factors that lead to poor soil productivity in Sub-Saharan Africa. The increase in population has driven the populace to inhabit marginal frontiers; worsening the erosion problem. This study evaluated the effects of some soil and water conservation (SWC) techniques on soil productivity and bean yield in Nyamasheke District; characterized by steep topography, higher precipitation and intensive agricultural activities. The study was conducted at Birembo watershed located in Macuba Sector. The specific objectives were (1) To identify common SWC techniques practiced and adoption challenges, (2) To evaluate the effects of SWC techniques on some soil physio-chemical properties, (3) To determine the effect of SWC techniques on soil loss, (4) To determine the effect of SWC techniques on bean crop yields. Semi-structured questionnaires were randomly administrated to 99 farmers to collect survey data. Field trials and soil analysis were used to record effects of SWC soil properties. Randomized complete block design replicated three times under bush beans production was employed. This was arranged in split plots with three levels of slope aspect: high (> 30%) , Medium (15-30%) and low (<15 %) being the main plot while the sub-plot constituted the four SWC techniques; Bench terracing + Agroforestry (BA), Bench terracing (BT),Contour bund (CB), Strip cropping (SC) and Control (C). The results revealed that all farmers recognized the negative impact of erosion on soil productivity, with 68% of farmers adopting SWC techniques and the majority of them (97%) implemented the techniques under the support of the Government and NGOs. The common SWC techniques used were agroforestry; accounting for about 45%, contour bund 29 and bench terracing 11%. In addition, 26% of the farmers adopted the combination of mechanical and biological measures for soil erosion control. Fallow, strip grass and ditches were used less frequently. Farmers did not implement soil erosion control due to poverty (51%), lack of materials (19%) and limited knowledge (16%). Furthermore soil texture, moisture and soil loss were significantly (p ≤0.001) affected by land slope and the techniques. The highest value of soil moisture of 27%, clay content 59% were recorded at low slope under BA and soil loss was zero under the same treatment at high slope. The BA treatment significantly (p≤0.001) affected soil pH, CEC and OC. However, CB and SC were not significantly different and had the lowest effects on these parameters. Slope and SWC techniques significantly (p≤0.001) affected soil nutrients (NPK) and bean yield. The highest values of N, P, K and yield were recorded in low slope plots and the highest bean yields were observed in BA with about 586kg.ha-1. The study recommends the combination of mechanical (bench terraces) and biological measures (agro-forestry) for improving soil productivity and bean yield.