SHORT-TERM RECOVERY OF BRADYRHIZOBIUM-JAPONICUM DURING AN INOCULATIONPROCESS USING MINERAL MICROGRANULES

Soybean (Glycine max (L.) Merr.) can be inoculated by delivering inocu lant mixed with mineral microgranules to the seedbed. An average decli ne of 0.61 log units in the number of viable Bradyrhizobium japonicum was found during the 1st h, using available commercial inoculants and granules. These losses were shown to be influenced by inoculant type ( pear based, liquid, lyophilized) and granule type. When mixed with gra nules, a peat-based inoculant was found to be desiccated immediately a nd subjected to a water potential as low as -170 MPa. Bradyrhizobium j aponicum recovery was improved when the moisture content of the granul es increased. It was concluded that water suction by granules can subj ect 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 t o improve the efficiency of this inoculation process.