Effect Of introduced Forage Legumes On Dry Matter Production, Nutritive Quality And Soil Fertility Of Natural Pastures Of Semiarid Rangelands Of Kenya

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Peter Ng'ang'a Macharia
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Peter Ng'ang'a Macharia
A two phase study was carried out in the semi-arid rangelands of Kaj iado District, Kenya, between October, 2002 and February, 2005. The major objective was to determine the effect of introduced forage legumes on production of natural pastures as a means of improving the quantity and quality of livestock feed while improving soil fertility. The specific objectives were: i) to screen potential forage legumes and select best performing ones for integration into natural pastures; ii) to detennine the effect of defoliation interval and height on dry matter production of grass/legume mixed pastures; iii) to detennine the effect of forage legumes on quality improvement of grasses in natural pastures; iv) to determine the effect of forage legumes on soil fertility improvement; and v) to determine moisture extraction by grasses and legumes in mixed pastures. During legume screening, five forage legumes were sown as monoculture stands in a Randomized Complete Block Design (RGBD).These were {Veonotonia wightii (Am.) Lackey (Glycine), Macroptilililn atropurpurellm (DC) Urb. (Siratro), Stylosanthes scabra var. seca Vog. (Stylo), Lablab purpllreliS cv. Rongai (L.) Sweet (Dolichos) and Mucuna pruriens (L.) DC (Velvet bean). The legumes were screened for their ability to grow and surviye under semi-arid conditions, increase of dry matter (DM) and litter production, and ability to enhance soil fertility. Data on OM production \vere collected at 2 and 4 months intervals at ground level and 15 cm heights of defoliation. Data on litter production were collected at the peak of long dry season in August. 2003. Soil samples for fertility analysis were collected at 0-15 cm soil depth before sowing the legumes and at end of experiment. The screening experiment sho\ved that Glycine, Siratro and Stylo withstood the semi-arid climatic conditions due to their perennial growth habit and produced high DM rate of 10.31, 7.81 and 3.52 t ha-1 y{l, respectively, Glycine, Siratro and Stylo produced high organic matter through litter fall which upon decomposition improved soil fertility by increasing soil pH, carbon, nitrogen and potassium. These legumes possessed deep tap roots and withstood heavy grazing and were self-propagating through dispersal of seeds. These three legumes were, therefore, selected for further integration with grasses in natural pastures in line with the first objective.