Studies on seed pelleting as an aid to legume seed inoculation. 4. Examination of preinoculated seed

Abstract

Samples of preinoculated legume seed were obtained from commercial outlets in southeastern Australia and compared with seed inoculated in the laboratory at currently recommended rates for the numbers of rhizobia associated with the seed and performance when grown in the field and in soil in a glasshouse. There were more than 100 times as many rhizobia on laboratory-inoculated seed as on preinoculated seed. There were no detectable rhizobia on three of the 48 samples of preinoculated seed examined, 22 other samples carried very low numbers, and all but one fell below standards derived from Australian lnoculant Research and Control Service requirements. When grown in soil containing naturally-occurring or added rhizobia, laboratory-inoculated seed was generally superior to preinoculated seed in percentage recovery of inoculant strains from nodules. The differences became greater as the size of soil populations of rhizobia increased. Where naturally-occurring rhizobia were few in number or absent nodulation was satisfactory provided that the seed carried viable rhizobia at time of sowing. The numbers of rhizobia associated with laboratory preparations of inoculated seed represented the potential standards that should be the commercial objective. The consistently lower numbers on preinoculated seed indicated that some stage (or stages) of the preinoculation process itself has a letha effect on the inoculant.