| Summary: | The occurrence of large numbers of legume species in the tropics with potentials for nitrogen fixation could be exploited to supply nitrogen, if they can be integrated into the farming system. The N2 – fixing potential of a native herbaceous leguminous species namely, Desmodium ramississimon (Dm) and grain legume, Vigna unquiculata (Cp) were studied in the green house and field, on three types of soil. In both situations, nodulation was influenced by the soil type. Nsukka soil, which had sandy texture, highest level of available phosphorus among the soils investigated in the study and moderate level of other plant nutrients (Mg and K) enhanced nodulation, which supported N-fixation. Soil type also influenced the quantity of N accumulated by each species, but had no effect on nitrogen concentration in the different plant parts. Desmodium ramississimon had higher nodule weight and accumulated more nitrogen and fixed more N2 than Vigna unquiculata in the three soils. The mean nodule dry weights were in the ranges of 61.6- 239.2 mg/plant for Dm in the three soils as compared to the range 3.2-31.4 mg/plant for Cp. Symbiotic dependence of DM varied with soil type ranging from 63.62% in Adani soil to 88% in Nkpologu soil, whereas Cp had the least symbiotic dependence value. These trends were confirmed in the field thereby indicating that Desmodium ramississimon had greater N2- potential than the cultivated legume studied.
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