Malo, Meshack Oguna2025-08-292025-08-292025-05https://ir-library.ku.ac.ke/handle/123456789/31314A thesis submitted in partial fulfillment of the requirements for the award of Doctor of philosophy in agronomy in the School Of Agriculture and Environmental Sciences of Kenyatta University, May 2025 Supervisors: Prof. Joseph Onyango Gweyi Prof. John Leju Celestino Ladu Dr. Joseph MukekaOvergrazing significantly alters the balance of carbon and nitrogen stocks in the soil by reducing plant biomass, impairing root development, and accelerating soil erosion. Continuous grazing pressure diminishes vegetative cover, which in turn limits the organic matter input crucial for maintaining soil organic carbon and nitrogen levels. This study aimed to assess the carbon stocks and nitrogen levels under varying grazing intensities in Central Equatorial State (CES), South Sudan. Specifically, it sought to (i) evaluate spatial variations in vegetation biomass, proxies to soil carbon stocks) (ii) evaluate temporal variations in vegetation biomass, proxies to soil carbon stocks, (iii) determine sector-specific spatial changes in Nitrogen stocks within Central Equatorial (iv) determine sector-specific temporal changes in Nitrogen stocks within Central Equatorial. Grazing intensities were characterized using vegetation biomass assessments, ground cover measurements, and livestock density tracking. Remote sensing and geospatial analysis were used to map grazing pressure in different counties. Grazing intensities were categorized as low, moderate, high, and very high. Soil samples were collected from the top 0-30 cm layer to estimate Soil Organic Carbon (SOC) and soil organic Nitrogen (SON). The sampled soils were tested in the laboratory according to scientific standards to ascertain carbon and nitrogen content. The Greening-Browning Fraction Index was used to assess vegetation health, cover, and changes over time to understand ecological changes. The findings revealed significant differences (p<0.05) in cattle numbers across varying grazing intensities, with Terekeka showing a "very high" intensity (≥150,001 cattle) and Kajo-Keji having a "low" intensity (≤50,000 cattle). Soil organic carbon and Nitrogen showed considerable variation across land-use categories at depths of 20 to 30 cm. Kajo-Keji County had the highest browning fraction (0.262) over an area of 3,514.47 sq. km. At the same time, Morobo County exhibited the lowest greening fraction (0.7031) across 982.071 sq. km. The results also highlighted a significant browning fraction index (p<0.05). Both organic carbon and organic nitrogen varied with soil depth with the contents significantly being higher in the top (0-10cm) soil (p≤0.01) compared to other profiles (10-20 and 20-30 cm). There were also variations of organic carbon contents depending of land uses and counties. The lowest organic carbon was recorded at watering points and congregation areas though there was no clear superiority of carbon content based on land uses. Lanya County consistently had higher carbon stocks at watering points (irrespective of soil depths), while Kajo Keji had higher C contents at congregation areas Terekeka had significantly higher C under agricultural land compared to the other counties (p≤0.01). The findings also revealed reducing trends of Nitrates with depth with soil depths, with the top (10 cm) having significantly higher C (p≤0.01). These findings would call for minimum tillage or no-till to retain the carbon on top soil since most plant roots are localized at the top when all resources are available. Moreover, the findings from this study will facilitate decisions to manage grazing intensities, improve livestock systems' and improve Carbon and Nitrogen stocks in South SudanenThesis