Effects of grazing management practices, topographic position, and land cover type on soil organic carbon fractions in semi-arid rangelands of Kenya

BACKGROUND: This study evaluated the effects of grazing management practices, topographic position, and land cover types on mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) in a semi-arid rangeland of Kenya. Research was conducted at Mpala Research Centre (controlled grazing) and Ilmotiok Community Group Ranch (continuous grazing) in Laikipia County. A factorial experimental design with a split-plot arrangement was used in this study. Grazing management practices (controlled and continuous grazing) and topographic positions (midslope, foot slope, and bottomland) were assigned to the main plots, while land cover types (bare ground, grass patches, and tree mosaics) were designated as subplots. Soil samples were collected at 10 cm intervals, 0-10 cm, 10-20 cm, and 20-30 cm depth for MAOC and POC analysis. Data analysis was done using R software, where nonparametric tests were done when the assumptions of normality and homogeneity of variance were violated. RESULTS: Controlled grazing resulted in higher MAOC (0.361%) and POC (0.683%) compared to continuous grazing (0.352% and 0.548%, respectively), indicating an increase of 2.56% in MAOC and 24.64% in POC under controlled grazing. This can largely be attributed to improved vegetation recovery, especially in midslope areas. The highest MAOC (0.367%) was found in the bottomland, likely due to reduced erosion and improved water retention. The midslope and foot slope positions had lower MAOC means of 0.358% and 0.344%, respectively. Depth analysis showed peak MAOC at 20 cm (0.390%), with controlled grazing resulting in better carbon retention at 30 cm. Similarly, controlled grazing yielded a mean POC of 0.683% versus 0.548% for continuous grazing, with bottomland having the highest POC of 0.754%. A Kruskal‒Wallis tests showed significant differences in MAOC and POC across land cover types (χ² = 42.701, p < 0.001 for MAOC, and χ² = 83.53, p < 0.001 for POC), with tree mosaics and bare land contributing most to POC and MAOC, respectively. CONCLUSIONS: These findings highlight the beneficial role of controlled grazing and diverse land cover in enhancing soil carbon storage. To promote sustainable rangeland management, it is recommended that rangeland managers adopt controlled grazing practices and allow diverse land cover types, such as tree mosaics, to increase carbon sequestration and ecosystem resilience.