HERBICIDAL EFFECTS ON CERTAIN SOIL MICROBIAL ACTIVITIES IN SOME BROWN SOILS OF SASKATCHEWAN

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Abstract
Summary. Amitrole, 2,3,6‐TBA, 2,4‐DB and di‐allate were applied at normal field rates to a loam soil in a preliminary study, The toxic effects, as measured by nitrification studies, persisted for 8 weeks after application. After a further 8 weeks this depressive effect was decreased.Residual effects were assayed by measuring the nitrification rate of soils following the application of the same four herbicides at two rates to four different soils. The residual effects of amitrole, di‐allate, 2,3,6‐TBA and 2,4‐DB were overcome 34, 28, 32 and 44 weeks respectively after treatment. Total microbial counts were also corelated with the nitrification rate of the soils. The trend of disappearance of the toxic effect of these chemicals was similar in all the soils in these laboratory investigations.Under field conditions the residual effect of amitrole, 2,3,6‐TBA and 2,4‐DB had disappeared by the end of 52 weeks, as far as could be determined by studies of nitrate production, ammonification and total counts of microorganisms. A second application of the chemicals 56 weeks after the initial treatment affected nitrification in the laboratory for only half as long, indicating adaptation of' the microorganisms to the herbicidesEffels des herbicides sur certaines activités des microorganismes du sol