Effects Of Selected Carrier Materials And Storage Temperatures On Survival, Viability And Efficacy Of Rhizobia Biofertilizers

ABSTRACT

Biofertilizers offer commercially feasible and environmentally sound means for supplementing nutrient supply to crops. The basic problem in acquiring quality rhizobia biofertilizers is the low number of efficient cells. The major limitations affecting the quality of rhizobia biofertilizers are; short storage duration, unavailability of appropriate carrier materials, and susceptibility to high temperature. The present study evaluated the effects of selected carrier materials and storage temperatures on survival, viability and efficacy of selected rhizobium strains used in rhizobia biofertilizers. Four selected carrier materials (peat, filter mud, cassava peels and Yeast Extract Mannitol (YEM) broth, five storage temperatures (-20 °C, 4 °C, 25 °C, 30 °C and 40 °C) were used to study the survival of two rhizobium strains (Bradyrhizobium Spp. USDA 110 and 532c). Biological and physicochemical properties of the carrier materials were determined before inoculating them with a known amount of rhizobium CFUs. The inoculated carrier materials were stored in different temperatures for six months. Samples from the carrier materials were taken after every two weeks and CFUs determined. The viability of rhizobia inoculants for the best carrier material after six months was determined under greenhouse conditions using soybean as the test crop. Presence of both fungal (except in peat) and bacterial contaminants was observed in the carrier materials hence the carriers were s sterilized before being used. The rhizobia population decreased over time regardless of carrier material and storage temperature. The population reduction was highest at 40 °C and lowest at 4 °C except in peat and YEM where reduction was lowest at -20 °C. The initial cell population and the cell population at the end of experiment (6 months) were significantly different (P