Evaluation of potential seed coating formulation with Bradyrhizobium japonicum on soybean (Glycine max L.) seeds

The seed coating technique can be used as a potential biofertilizer delivery strategy. This study sought to formulate a low-cost potential seed coating mixture for soybean (Glycine max L.) seeds, applied with Bradyrhizobium japonicum and assess the viability of the bacterium on the seed coat during storage. Seed coating mixture was formulated by using xanthan gum and biochar as the binder and the filler respectively in the ratio of 80g:20g. The formula was further checked with three different xanthan gum concentrations (0.25%, 0.5% and 1%) each with and without sucrose (1%W/V). The selected coating mixture was inoculated with Bradyrhizobium japonicum (3×10⁸ CFU/ml) and tested after 20 days of storage at two different temperatures (4℃ and 30℃) for Bradyrhizobium survivability and seed germinability. The germination percentage was significantly higher (p<0.05) in both coated and non-coated seeds stored at 4℃ compared to 30℃. Germination percentages of non-coated seeds were higher under both temperatures. Initially, the survivability of the bacterial population after seed application was around 1×10⁷ CFU/ml in the seed coating but significantly dropped after three days in both temperatures. At the end of the 15^th day the survivability of the inoculum was maintained to over 7×10⁵ CFU/ml under 4℃. The formulated seed coating is effective for its transient capacity in maintaining the viability of Bradyrhizobium japonicum at lower temperatures. This can be developed as a potential biofertilizer to hold and later deliver to the field soil via seeds.