Respiration Rates and Plate Counts for Determining Effect of Herbicides on Heterotrophic Soil Microorganisms

Interactions between herbicides and plant pathogens

“…The herbicides 2,3,6-TBA, EPTC, diuron, and simazine decreased the rate of carbon dioxide evolution from soil for at least 28 days (CHANDRA et al 1960). Dinoseb reduced respiration and plate counts of the saprophytic microHora for three months (GAMBLE et al 1952). The use of amitrole, 2,3,6-TBA, 2,4-D, and diallate resulted in reduced bacteria, actinomycete, and fungus counts (CHANDRA 1964).…”

Cyanobacteria and pesticides

“…Nitrogen-fixing cyanobacteria are also used for study of effects of 2,4-D. Tolypothrix tenuis was inhibited by 0.5 ppm of 2,4-D (Gamble et al 1952). A slight stimulation of growth of T. tenuis was reported in soils by 2,4-D at 0.04 ppm (Platonova 1967).…”

The effect of certain pesticides on nitrification in the soil

“…Smith, Dawson, and Wenzel (10) reported that 2,4-D had no significant effect upon total plate counts of bacteria, actinomyces, and fungi, even at 100 ppm concentration, but the number of nitrite-and nitrateformers were decreased, although recovery took place in ten to forty days. 3 Smith and Wenzel (11) found chlordane to be less toxic to the nitrifiers than BHC. Jones (5) reported that both chlordane and BHC had some inhibitory effect upon the nitrifiers when the concentrations of the toxicants were above 1,000 ppm.…”

“…Gamble, MayheM^and Chappell (3) reported that the herbicides dinitro-o-secondary butyl phenol (3 pounds per acre) and ortho-chlorophenol-sulfonyl fluoride (20 pounds per acre) reduced the respiration rate and plate counts of the saprophytic microflora for three months after treatment. 3 (para-chlorophenyl) 1,1 -dimethyl urea (2 pounds per acre) showed a similar reduction for one month.…”