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. Semistructured
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.