Exploring the distribution of soil properties across an open-grazed pastoral system in Laikipia rangelands, Kenya

Abstract

Laikipia rangelands in Kenya are among the most productive ecosystems but there is concern that the traditional free grazing regimes may accelerate soil and vegetation deterioration. We investigated the distribution of soil properties in the rangelands of Ilmotiok ranch in Laikipia County where grazing is predominantly open or free and examined selected soil chemical properties and particle size distribution in three types of habitats (tree, grass and bare ground) along four transects, placed diagonally across hillslope positions. We focused our study on the hypotheses that habitat types and hillslope position had an effect on soil properties distribution along the profile. Along each identified transect, soil samples were collected at four depths 0–10, 10–20, 20–30 and 30–40 cm. Distribution of soil properties mainly carbon, total nitrogen and phosphorus were influenced by hillslope position and habitat type and their contents decreased gradually with soil depth. Soil organic carbon content was high in tree habitats while in grass habitats average total phosphorus content in the profiles was slightly lower than in tree habitats. Total soil nitrogen was highest in the footslope in the tree and grass habitat and ranged between 0.81−2.17 g/kg and 1.26−2.50 g/kg, respectively. Sand was the dominant grain size fraction which accounted for 50−88%. This study demonstrated that there are soil fertility differences in the rangelands caused by vegetation cover and hillslope positions which are particularly important for future agro-pastoral use decisions.