Using Forage Legumes to Improve Soil Fertility for Enhanced Grassland Productivity of Semi-arid Rangelands of Kajiado District, Kenya

Abstract

A two-phase study was conducted in the semi-arid rangelands of Kajiado District, Kenya, to determine the effect of forage legumes on soil fertility improvement and grassland productivity of natural pastures. During legume evaluation phase, Neonotonia wightii (Glycine), Macroptilium atropurpureum (Siratro), Lablab purpureus cv. Rongai (Dolichos), Mucuna pruriens (Velvet bean) and Stylosanthes scabra var. seca (Stylo) were screened for adaptability and growth performance. Results of soil analysis showed that soil pH, organic carbon, nitrogen and potassium significantly increased after 2 years of study due to the large amounts of organic residues produced by the legumes (particularly the perennials). The calcium content decreased significantly (which was attributed to plant uptake) while the decrease of phosphorus was not significant. After integration of Glycine, Siratro and Stylo into natural pastures during the second phase of the study, the crude protein content of grasses intercropped with legumes increased from 7.1 to 14.3, 11.9 and 10.2%, respectively. Grasses intercropped with legumes also had higher digestibility contents than grasses in monoculture stands. The study concluded that addition of organic residues by the introduced forage legumes improved the soil fertility status and hence the crude protein and digestibility of grasses.