Soil Organic Carbon Content and Stocks in Relation to Grazing Management in Semi-Arid Grasslands of Kenya

Abstract

Rangelands cover approximately 85% of Kenya’s land mass and is a major resource for livestock farming with a considerable potential to mitigate climate change, yet these lands are stressed differently by various management. Our study aimed at determining the influence of grazing management systems (rotational, continuous and ungrazed) on soil organic carbon stocks in Yoani ranch located in the southern rangelands of Kenya (2016). This research was conducted on a commercial grazing ranch, a section of it was converted from continuous grazing into rotational grazing and has been under rotational grazing for 11 years during the time the research was conducted. Within the same ranch, there was a section with similar geomorphology and soils as the rotationally grazed which was not converted and has been continuously grazed for over 30 years to represent the continuous grazing system. The ungrazed area consists of an abandon section of the ranch for more than 30 years due to a deep gully which was formed by gully erosion creating an isolated area inaccessible by livestock. Soil samples were taken up to a depth of 1.2m, at an interval of 0-10, 10-20 cm, 20-30 cm, 30-60 cm, 60-90 cm and 90-120 cm. The difference between soil sampling depths is because the upper layer between 0-30 cm is more dynamic with respect to soil microbial activities which can be influenced by grazing as compared to the deeper depths along the soil profile. The ungrazed site recorded significantly (P<0.5) higher soil organic carbon concentrations than rotational and continuously grazed sites for all soil layers up to 1.2m depth. The rotationally grazed site had higher soil organic carbon concentrations across depths compared to continuously grazing system which was attributed to grazing management effects.