Changes in microbial numbers and activities in two non-flooded soils treated with bensulfiiron-methyl at 16 and 160 µg/kg were studied after 1 and 4 weeks of incubation under laboratory conditions. In addition to herbicide persistence, six general and functional microbial groups (numbers of culturable aerobic and anaerobic bacteria, aerobic N 2 fixers, autotrophic nitrifiers, aerobic and anaerobic cellulolytic microorganisms) and two activities (respiration and nitrification) were also studied. With respect to microbial numbers, only cellulolytic microorganisms in soil which had never been previously treated with pesticides significantly decreased in number. Only the higher dose of bensulfiiron-methyl in the second soil 381
Liquid cultures of Bradyrhizobium japonicum were added in a 1:1 ratio to 20% aqueous skim milk, or centrifuged and the cells resuspended in 10% skim milk. The suspensions were stored at —20° or —80°C for 7 months and cell survival assessed. At —20°C, there was a decrease in the viable count of about two logs in liquid culture whilst for cells resuspended in 10% skim milk the decrease was limited to one log. The temperature of —80°C was found to be in itself protective and the surviving rhizobial cells maintained their infectivity and effectiveness. Thus appropriate freezing conditions provide a suitable method to store soybean rhizobia cells prior to preparing the legume inoculant.
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