Abstract
Adoption of legume inoculation with rhizobia by small-scale farmers in East Africa, and the resultant increase in biological nitrogen fixation requires that quality inoculants meet minimum standards. BIOFIX is one of the commercially available rhizobia/legume inoculants in East Africa, whose standard is at least 109 rhizobia g-1. We examined the effect of carrier material and storage conditions on the populations of two industry standard rhizobia, Bradyrhizobium japonicum USDA 110 for soybean (Glycine max) and Rhizobium tropici CIAT 899 for common bean (Phaseolus vulgaris) over 165 days, using the drop plate method on Congo Red Yeast Extract Mannitol Agar. Viable populations of rhizobia differed significantly between carriers and rhizobia strains (P<0.05). Rhizobium tropici CIAT899, prepared with filter mud carrier, achieved a shelf-life of 135 days and B. japonicum USDA110 contained over 109 cells g-1 for 105 days. Both of these results fall below the stated six months expiry period of BIOFIX. Replacing filter mud carrier with vermiculite, resulted in an inferior product; although, both more thorough sterilisation and refrigerated storage, after a 14 day curing stage, improved the shelf-life thizobia in the inoculant packet.Keywords: BIOFIX, CIAT 899, Kenya, USDA 110
Highlights
Wider use of legume inoculants by African smallscale farmers, offers potential for a sustainable source of nitrogen and increase nutrient-use efficiency (Dieker et al, 2011)
Rhizobium tropici CIAT899 and Bradyrhizobium japonicum USDA110 strains were cultured in yeast extract mannitol broth, for seven days, on a rotating shaker, resulting in a log-phase broth culture of >108 cells ml-1
Among the three sources of inoculant examined at Mircen Laboratory, filter mud held large numbers of rhizobia population for both strains R. tropici CIAT 899 used bean and B. japonicum USDA 110 for soybean (Table 2)
Summary
Wider use of legume inoculants by African smallscale farmers, offers potential for a sustainable source of nitrogen and increase nutrient-use efficiency (Dieker et al, 2011). The inoculants must be of the desired quality to effectively nodulate legume hosts and offer strong economic returns (FAO,1984). Nodulation is improved when the number of viable rhizobia cells inoculated per seed increases. This is accomplished by having more viable rhizobia cells in the inoculant or delivering larger doses (Catroux et al, 2001). It is important to determine the duration of the bacteria survivability in different carrier materials, to ensure that the expected level of bacterial population remains viable for the inoculants to be effective. The solid carrier materials should bear properties that protect rhizobia and permit easy application to seeds (FAO, 1984)
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