Short-term recovery of Bradyrhizobium japonicum during an inoculation process using mineral microgranules

Soybean (Glycine max (L.) Merr.) can be inoculated by delivering inoculant mixed with mineral microgranules to the seedbed. An average decline of 0.61 log units in the number of viable Bradyrhizobium japonicum was found during the 1sth, using available commercial inoculants and granules. These losses were shown to be influenced by inoculant type (peat based, liquid, lyophilized) and granule type. When mixed with granules, a peat-based inoculant was found to be desiccated immediately and subjected to a water potential as low as −170 MPa. Bradyrhizobium japonicum recovery was improved when the moisture content of the granules increased. It was concluded that water suction by granules can subject the bacteria to rapid desiccation and significantly decrease their number. Thus, the nature of inoculant and granular material and their relative water retention characteristics must be taken into account to improve the efficiency of this inoculation process.Key words: Bradyrhizobium japonicum, granular inoculant, inoculation, soybean, survival.