Comparison of Inoculant and Indigenous Rhizobial Dinitrogen Fixation in Cowpeas by Direct Nitrogen‐15 Analyses

Abstract

Soil that contained 15N enriched organic matter (0.461 % 15N) was used to determine competitiveness of six strains at different logarithmic inoculum densities against indigenous rhizobia and against a previous surviving inoculant (strain P132). Analyses of N content of plant tissues by direct 15N technique showed that cowpeas (Vigna unguiculata L. Walp.) were capable of deriving 60 to 98% of shoot N from N2 fixation. The two fast‐growing strains (176A26 and 176A28) were poorer competitors and fixed less N2 compared to the other slow‐growing strains. Inoculum density had no effect upon yield response of cowpeas, but inoculation with strains P132, 401, and 22A1 effected greater seed yield, shoot dry matter, total N, and percentage of N derived from fixation (86‐98%) than other strains and the uninoculated control (60‐73%). By contrast, N2 fixation and yield parameters in inoculated cowpeas were not significantly different from inoculated controls that contained residual P132 from a previous inoculum study. The higher hydrogen uptake (Hup) efficiency of nodules containing residual P132 (98 ± 2%) facilitated presumptive identification of P132 (100% ± 0 Hup efficiency axenically) as the surviving and infecting inoculant strain since nodules infected by indigenous rhizobia had lower Hup efficiencies (88 ± 2%).

Trifolitoxin Production and Nodulation Are Necessary for the Expression of Superior Nodulation Competitiveness by Rhizobium leguminosarum bv. trifolii Strain T24 on Clover

“…Examples of very competitive strains in mixed inoculum include Rhizobium sp. P132, a member of the cowpea miscellany (10), strains in serogroup 123 of Bradyrhizobium japonicum (19) uminosarum bv. viceae strain PF2 (8), and antagonistic strains of Rhizobium leguminosarum bv.…”

Root Characteristics and Seed Yields of Cowpeas Grown with and without Added Nitrogen Fertilizer

“…The efficiency of effective nodulation in supplying the cowpea plant's N requirement is well documented (ElHassan and Focht, 1986;Summerfield et al, 1977). Despite this fact, the use of commercial N fertilizers in cowpea production remains a common recommendation (Fernandez and Miller, 1986;Halsey, 1960).…”

Effect of salt stress on nitrogen fixation by different cultivars of green beans

“…A number of researchers studied the N 2 fixation and nodulation of legumes under normal (non-stressed) conditions (7,11,12,15). Broadbent et al (7) reported that clover (Trifolium repens L.) could fix about 85 to 100% of its N under normal (non-stressed) field conditions.…”

“…Broadbent et al (7) reported that clover (Trifolium repens L.) could fix about 85 to 100% of its N under normal (non-stressed) field conditions. El-Hassan and Focht (11) found that cowpea (Vigna unquiculata L. Walp) obtained 60 to 98% of its shoot N from N 2 fixation, and the rhizobium partner effectiveness affected the N 2 -fixation rate dramatically. About 66 to 97% of N in soybean (Glvcine max L.) was provided through its atmospheric N 2 fixation according to George et al (15).…”