Effect of rangeland rehabilitation on soil physico-chemical properties and diversity of herbaceous layer in Suswa catchment, Narok County

Author: Ombega, Joseph

Supervisors: Stephen M.; Anne Karuma and Oscar K.

Land degradation is a global challenge and its effects on plant and soil biodiversity are profound and negative. Land degradation negatively affects soil fertility and plant diversity and hence people’s wellbeing. This study assessed the effect of land rehabilitation on soil physico-chemical properties and diversity of herbaceous layer in a severely degraded rangeland in Suswa catchment, Narok County, Kenya. Vegetation attributes (Above ground Biomass, Total Cover, Composition, Relative abundance, Richness and Diversity of herbaceous layer) and soil parameters (Bulk Density, Aggregate Stability, Texture, Hydraulic Conductivity, Penetration Resistance, Moisture Content, Nitrogen, Organic Carbon, soil pH, Potassium and Phosphorus) were determined within the rehabilitated and degraded areas along a slope (upper, middle and lower slope positions). Within each slope position three 100 m transects were laid 30 m apart. Vegetation attributes were then determined along each transect at intervals of 1m. Soil parameters were also collected at intervals of 25 m using a soil auger for laboratory analysis. The results of the analysis showed that herbaceous biomass production, diversity, relative abundance, composition and richness of perennial grasses significantly (P ≤ 0.05) increased downslope being higher in the rehabilitated area than in the degraded area. The highest biomass production (1,459 kg/ha) and ground cover (74.67 %) were recorded in the lower slope rehabilitated area. Similarly, soil moisture content, aggregate stability, porosity, hydraulic conductivity, total organic carbon, nitrogen, available phosphorus and potassium significantly (P ≤ 0.05) increased downslope being higher in the rehabilitated area than in the degraded area. Conversely, the diversity, relative abundance, composition, percent cover, species richness and aboveground biomass of forbs and annual grasses significantly (P ≤ 0.05) increased upslope with higher values recorded in the degraded area. The mean bulk density, % sand and penetration resistance were significantly (P ≤ 0.05) higher in the degraded area and increased upslope with highest bulk density (1.21 g/cm3) and sand content (85 %) recorded in the upper slope degraded area. This study clearly demonstrates that with proper land management soil and vegetation diversity can be greatly improved. However, in areas with steep topographical gradient use of structural soil and water conservation techniques such as retention ditches, cut off drains and terraces is highly recommended.