Effects of Methyl Bromide Dosage on Microorganisms in Soil Before and After Growth ofNicotiana glutinosa

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Abstract
Soil fumigation for various periods with a controlled concentration of methyl bromide (MB) in a moving airstream affected the populations of various microorganisms. In soil fumigated with 27,000 .mu.l of MB/l of air, soil fungi and Pseudomonas spp. were eliminated within 16 h, Streptomyces spp. were greatly reduced within 64 h and were undetectable in soil fumigated for 128 h; but aerobic bacteria and Bacillus spp. were only slightly affected by treatment for 128 h (the longest time tested). Soil was treated with 32,000 .mu.l of MB/l of air for various times, planted with N. glutinosa, and microbial populations also were determined in nonfumigated soil planted with N. glutinosa. Microbial populations of soil in which plants had been grown increased as the time after fumigation increased. After 89 days, populations of fungi in soil fumigated for 32 or 128 h were as great as those initially found in nonfumigated soil. Penicillium spp. and Trichoderma spp. were the dominant fungi isolated from soil after fumigation for longer than 8 h. Recolonization of fumigated soil by Streptomyces spp. was rapid; after 38 days, numbers were greater in soil fumigated for 32 h than those in nonfumigated soil. Recolonization by Streptomyces spp. was slow in soil fumigated for 128 h and populations after 89 days were still lower than those in nonfumigated soil. Populations of aerobic bacteria and Bacillus spp. were greater in soils fumigated for 32 or 128 h than in nonfumigated soil at all sampling periods. Fluorescent Pseudomonas spp. were not isolated from fumigated soils in which N. glutinosa was grown, but they were present in planted nonfumigated soils.