Effect of phosphorus on nodulation and dry matter yield of legume green manure species in the humid highlands of Kenya
2002
Ojiemi. 0(KARI-National Agricultural Reseach Centre, Kakamega, Kenya) | Mureithi, J.G.(Kenya Agricultural Research Institute, Nairobi (Kenya). National Agricultural Research Laboratories) | Maobe, S.N.(KARI-Regional Reseach Kisii, Kenya) | Okwuosa, E.A.(KARI-National Agricultural Reseach Centre, Kakamega, Kenya) | Nekesa, C.(Kenya Agricultural Research Institute, Nairobi (Kenya). National Agricultural Research Laboratories)
Legume green manure species have the potential for improving soil fertility by fixing atmospheric nitrogen. However, application of phosphorus (P) is essential for high dry matter (biomass) yield and effective nodulation. Recent research findings suggest that plant species and cultivars differ in ability to utilise available forms of P. Effect of four (0, 20, 30, and 40 kg P ha-l) rates of P on nodulation and biomass yield of nine legume green manure species; Crotalaria ochroleuca, Crotalaria juncea, Calopogonium mucuniodes, Lablab purpureus cv Rongai, Canavalia ensiformis, Mucuna pruriens, Glycine max, Neonotonia weightii, and -Vicia benghalensis, was determined at Kakamega, Kabete, and Kisii, all within the humid Kenya highlands. Biomass accumulation was low at all sites due to pests, diseases, and drought. Phosphorus had no significant (p=0.05) effect on either biomass accumulation or nodulation at any of the sites. However, averaged across species, application of P increased biomass by 0.72 t ha-l at Kabete and 0.62 t ha-l at Kakamega. No increase was recorded at Kisii. P had no significant effect on nodulation but the number of nodules per plant increased slightly. The highest increases were obtained with (:rotalaria ochroleuca (11), Mucuna pruriens (4), and Glycine max (3). With the exception of Crotalaria ochroleuca, the species had no nodules with red inner tissue indicating they were probably not active. These results suggest that P may not be critical for biomass accumulation and nodulation. However, there is need to establish the threshold P levels for legume species in different sites in Kenya. In addition, use of more quantitative methods in assessing nitrogen fixation may be necessary.
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