Influence of soil physical factors on productivity of herbaceous forage species in Kivaa and Ntugi rangelands in Eastern Kenya

Abstract

Rangelands are extensive tracts of land with natural vegetation which is the main forage resource for domestic and wild ungulates. This study investigated the influence of soil texture, bulk density, and moisture content on the production of herbaceous forage species biomass in Kivaa and Ntugi rangelands in Eastern Kenya. Stratified random sampling was used where one out of four blocks of the target rangelands was picked and three belt transects established. Along the belt transects, ten experimental plots of 5 metres by 5 metres were established at intervals of 5 metres. Key forage species were identified using a structured questionnaire administered to key informants. Soil samples were collected from the experimental plots and analyzed for soil texture, bulk density and moisture content. Forage samples were collected and dry matter weight determined. The data collected were analyzed using both descriptive and inferential statistics especially tabulation and regression respectively. The study identified the most valuable forage species namely, Dichanthium annulatum, Themeda triandra, Cenchrus ciliaris, Rhynchelytrum repens, Digitaria abyssinica, Chloris roxburghiana and Cyperus rotundus. Soils in Ntugi ranged from clay loam to sandy clay while those from Kivaa ranged from silty loam to sandy loam. There was higher moisture content in soils in Ntugi than soils in Kivaa (t = 7.71, P ≤ 0.05). Soil moisture content had significant influence on herbage production in both Kivaa (R= 0.968, P ≤ 0.05) and Ntugi (R = 0.962, P ≤ 0.05). Soil bulk density significantly influenced forage grass species herbage production in Ntugi in 2014 (R= 0.513, P ≤ 0.05) and in 2016 ((R = 0.632, P ≤ 0.05). This study concluded that soil texture, bulk density and moisture content significantly influenced herbaceous forage production in the two rangelands. The study recommends use of rotational grazing systems combined with proper stocking rates to maintain moderate soil bulk density and good levels of soil moisture for the herbaceous forage species to continue producing adequate biomass while maintaining residual foliage for continued primary production.