Abstract

Effective nodulation of legume is usually solid carriers dependent. Peat, the most effective solid carrier is not readily available in Nigeria, hence, alternative solid carriers were evaluated with Bradyrhizobium strains using cowpea as a test crop. Mutant strains (USDA 3384 and USDA 3451) were evaluated in the laboratory using solid carriers and pot experiments. The survival (multiplication), infectivity and nodulating ability of the Bradyrhizobium mutant strains using cowpea as a test crop were assayed in peat, cowdung and composted maize cob. Mutant strains inoculated in the three solid carriers got to their peak of growth at 16^th day of incubation. Peat significantly (p<0.05) increased the population of both USDA 3384 and USDA 3451 compared to cowdung and composted maize cob. USDA 3451 inoculated in cowdung significantly (p<0.05) increased multiplication of Bradyrhizobium mutant strain and nodulation of cowpea. Investigation shows it can be used as peat substitute when preparing inoculant. USDA 3384 inoculated in both composted maize cob and cowdung, respectively had consistent and significant positive effect on nodulation of cowpea and nodule dry weight. These results reveal their ability to subtitute peat. Hence, blind use of alternative solid carriers for inoculant preparations may hinder high infectivity and optimal nodulation which could facilitate positive effects of nitrogen fixation in low N tropical soil.

Key words: Solid carriers, Bradyrhizobium,survival, infectivity, nodulation.