Effect of Burning Natural Pasture on Soil Chemical Properties and Dry Matter Production of Introduced Glycine and Siratro Grass Legume Mixed Pastures In Semi-Arid Rangelands of Kenya

Abstract

Fire is often used as g tool to stimulate new pasture growth that is of higher quality. However, fire has profound effects on the soil's nutrient dynamics and dry matter (DM) production of the pasture. This study was conducted in Kajiado District to study the effect of pasture burning on soil chemical properties and dry matter yield (DM) of introduced Neonotonia weight (Am.) Lackey (Glycine) and Macroptilium atropurpureum (DC) Urb (Siratro) forage legumes. On one site, herbage was subjected to a back fire while herbage in an adjacent site was slashed to ground level. Before planting the legumes, soil samples were collected at 0-15 cm depth and analyzed for pH (H20), organic carbon (C), nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca). The results showed that the soil pH in the burned site (5.25) was higher (though not significant at PS:0.05) than in slashed plots (5.06). The soil organic C and N was higher in slashed plots than in burned plots. However, the soil's P, K and Ca levels increased after burning with P achieving a significant increase while the increase in K and Ca was not significant. Specifically, the soil N content was significantly higher in slashed (0.17 %) than in burned plots (0.15 %). The soil P was higher in burned (177.9 ppm) than in unburned plots (166.8 ppm). Potassium levels in burned plots (1.25%) was higher (though not significant) than in slashed plots (1.20 %). Calcium levels were also higher (though not significant) in burned (5.34 %) than in slashed plots (5.12 %). Glycine grown as monocultures yielded more DM in burned site (6.87 tlha) than in slashed plots (4.81 tlha). Monoculture stands of Siratro yielded more DM in slashed plots (2.84 tlha) than in burned plots (2.73 tlha). When the two legumes were grown as mixtures with natural pasture, the pattern was the same as in monocultures.