Effect of polymer additives on viability of Rhizobium japonicum in Molasses-based liquid organic fertilizer

Maintaining the viability of microbial cells during storage is required to commercialize the liquid organic fertilizer-based product. Various polymer additives can maintain the viability of microbial cells in liquid organic fertilizer (LOF) during storage. This study aimed to analyze the effect of polymer additives on the viability of Rhizobium japonicum RB2 in molasses-based liquid organic fertilizer during six months of storage. This experiment used glycerol 0.5% and polyvinyl pyrrolidone (PVP) 0.5% as polymer additives. The treatments consisted of (i) LOF, (ii) LOF+PVP, (iii) LOF+Glycerol, and (iv) LOF+PVP+Glycerol. A completely randomized design with six replications was employed in this study. In addition to bacterial viability in the LOF, chemical properties (pH, total dissolved solids/TDS, and Brix) were also monitored. The results showed that the pH values in all treatments decreased, possibly due to increased organic acids secreted by bacteria. LOF+polymer additives showed higher bacterial viability than LOF without polymer additives. However, at six months of storage, the mean shelf life of the bacterial population decreased in all treatments from 7.40–8.39 log10 CFU/mL to 4.97–6.19 log10 CFU mL−1. The decrease in bacterial viability was related to the high TDS and Brix values in molasses-based LOF, which caused the bacteria to lose water through osmosis. The results indicate that adding polymer additives such as glycerol and PVP in high-sugar molasses-based LOF does not always positively affect bacterial viability.