Browsing by Author "Ako, Akonaay Michael Leonard"

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    Studies on symbiotic nitrogen fixation of some Crotalaria species
    (University of Dar es Salaam, 1993) Ako, Akonaay Michael Leonard
    This study was mainly concerned with assessement of symbiotic N2 fixation in crotalaria species, and some biochemical properties of their rhizobial isolates. Some important findings from the study are presented below. Physiological differences among the rhizobial strains were noted in terms of carbohydrate utilizations and antibiotic susceptibilities. However, their general characteristics indicated them to belong to a category of slow-growing rhizobia, rather than the fast-growing ones. The importance of some sugar as carbon sources to those strains, as well as possible significance of using some antibiotics in the rhizobial strains isolation has been highlighted. Six Crotalaria species, namely C. ochroleuca, C. retusa, C. natalitia, C. laburnifolis, C. kirkii, C. laburnoides were grown in four types of potted field soils in the greenhouse. Their growth, nodulation and symbiotic N2 fixation was found to vary with soil type and plant genotype. Comparison among them showed C. achroleuca to be superior over other species. Effects of rhizobial inoculation and urea-N to growth, nodulation and symbiotic N2 fixation of four Cratalaria species, namely C. ochroleuca, C.retusa, C. natalitia, and C.kirkii was studied in potted field soil. Application of urea-N at 20mg/kg soil was found to be beneficial to nodulation and symbiotic N2 fixation. Inoculation with rhizobial strains indicated that, negative effects due to high levels of urea-N application can be alleviated. Differences in response to high urea-N levels by the plant species was noted, whereby C. ochroleuca indicated to be more tolerant to high levels of urea-N than other species tested. Effect of N source on modulation and symbiotic N2 fixation was studied in C. ochroleuca, by using a modified Leonard jar assembly. Nitrate-N was found to be more inhibitory to nodulation and symbiotic N2 fixation than urea-N. Urea was noted to be a more compatible N source with legume-Rhizobium symbiosis in C. ochroleuca than nitrate. Perfomance of C. ochroleuca was evaluated under different growth stages in the field. Its nodulation and symbiotic N2 fixation capacity was found to increase with plant age, reaching maximum near flowering stage. Application of C. ochroleuca shoots near flowering as a green manure in a field, increased the organic C, total N content and available N in soil. The legume also significantly increased a yield of subsequent maize crop. It was noted that N from C. ochroleuca can be efficiently utilized by maize, compared to that from urea fertilizer.