Herbicidal Effects on Certain Soil Microbial Activities in Some Brown Soils of Saskatchewan

Abstract

Amitrole, 2,3,6-TBA, 2,4-DB and di-allatc 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 hy measuring the nitrification rate of soils following the application ofthe same four herhicides at two rates to four different soils. The residual effects of amitroie. di-ailate, 2,3,6-TBA and 2.4-DB were overcome 34, 28, 32 and 44 weeks respectively after treatment. Tolal microhial counts were also correlated with the nitrification rale ofthe soils. Tlie trend of disappearance of the toxic effect of ihest-chemicals was similar in all ihe 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 tie determined by studies of nitrate production, am mo nifi cation and tolal counts of microorganisms. A second application of ihe chemicals 56 weeks after the initial treatment affected nitrification in the laboratory for only liaM a.s long, indicating adaptation of thf microorganisms lo the herbicides. Effets des herbicides sur certaines activit4s des microorganismes du sotResum^. Dans une dtudc preliminaire, l'amilrole, le 2,3,6-TBA, le 2,4-DB et le di-allate ont m appliquds aux doses normales d'emploi sur un sol argileux. Les effets toxiques evaluds par lVtude de la lutrification persisttrent pendant les 8 semaines qui suivirent ['application. Apres 8 autres semaines, l'effet depressif alia en decroissant.Les effets riisiduels fureni ^valu^s en mesurant le taux dc nitrification des sols apr^s l'application des quatre memes herhicides, ^ deux doses, et ceci dans quatre sols dilft^rents. Les effets r^sidurls dc I'amitrole, du di-allate, du 2.3,6-TBA et du 2,4-DB disparurent respectivemriit 34, 28, 32 et 44 semaines apr^s le traitcment. Les complages tolaux de microorganisnics montrerent aussi une correlation avec le taux de nitrification des sols. L'allure gen^rale de la disparition de l'effet loxique de ces produits fut similaire dans tous les sols Studies au lalxjratoire.En plein champ, l'effet residue! de t'amitrole, du 2,3,6-TBA et du 2,4-DB disparait apres 52 semaines, pour autant que i'on en puisse juger par I'etude do la production de nitrate et d'ammoniac et par le comptage des microorganismes. Uiic seconde application des produits 36 semaines apres le traitement initial n'affccta la nitrification au laboratoire que pendant une periode moitie moins iongue, ce qui indique une adaptation des microorRanismes aux herbicides. Die Wirkung con Herbiziden auf gewisse mikrobielU Prozesse im Boden Zusammenfassung. Amitrol, 2.3,6-TBA, 2,4-DB und Di-ailate wurden in einem Vorversuch in normalen Aufwandmengen auf Lehmboden angewandt. Die mit Hilfe von Nitrifikationssiudien festgestellle toxische Wirkung hii-ll iiber 8 Wochen langan.Nach weiteren 8 Wochen war die hemmende Wirkung verniiiidert. Die Riickstandswi...

Tillage effects on soil microbial and biochemical characteristics in a fallow-wheat rotation in a Dark Brown soil

“…Thus, these results support the observations and hypotheses advanced by others who have worked with these and other herbicides (Chandra 1964;Tu and Bollen 1968;Grossbard 1985;Biederbeck et al 1987;Moorman 1989). For example, in a review paper, Moorman (1989) concluded that total microbial populations in soils are often unaffected, or only slightly affected, by pesticide applications, although individual species, such as cellulose decomposers, may be greatly affected.…”

Studies on the Effects of Herbicides on Soil Nitrification*

“…It is very unlikely that 850 ppm would be reduced to 100 ppm (see Table 2) during the perfusion period and the clear change in sensitivity finds its most logical explanation in a direct adaptation of the nitrifying organisms to herbicide toxicity. Chandra (1964), who also recorded inhibition of nitrification by 2,3,6-TBA, obtained evidence of a similar adaptation.…”

Interactions between herbicides and plant pathogens

“…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). Paraquat increased the total number of fungi and percentage of penicillia but decreased mucors in one soil and not in another (Tu and BOLLEN 1968).…”