Chemical Versus Microbial Decomposition of Amitrole in Soil

Abstract

Degradation of 3-amino-l,2,4-triazole-5-C14 (amitrole-5-C14) in autoclaved, potassium azide, ethylene oxide, and dry-heat sterilized soil was compared with that observed in nonsterile soils by measuring evolved C14O2. Amitrole degradation occurred in azide and ethylene oxide-sterilized and nonsterile soils but not in autoclaved soils. Only slight degradation occurred in autoclaved soil re-inoculated with mixed cultures of soil microorganisms isolated from soil in which amitrole had been rapidly degraded. Addition of EDTA-Na to nonsterile and ethylene oxide sterilized soils reduced amitrole degradation. Addition of organic amendments to amitrole treated soil stimulated microbial activity but reduced amitrole degradation. Addition of specific metallic salts to certain soils increased the rate of amitrole degradation. Amitrole degradation occurred rapidly in several free radical generating chemical systems. These results and additional observations indicate that amitrole degradation, at least in three soils examined, was largely a chemical process, and that microbial involvement was only indirect.

Factors Influencing Microbial Degradation of14C-Glyphosate to14CO2in Soil

“…Phos phate additions to the Norfolk soil essentially had no effect on 14 C-glyphosate degradation (Table 3). It was expected that 14, 4 addition of phosphate would increase 14 C-glyphosate avail ability to a limited extent by competing with 14 C-glyphosate for sorption sites. Glyphosate is believed to be bound to soil constituents through the phosphonic acid moiety and com petes with inorganic phosphate for available sorption sites (1,9).…”

“…Factors influencing microbial activity such as pH, moisture, temperature, organic substrate availability, and nutrient levels are known to affect herbicide degradation in soil (3). Attempts have also been made to in crease herbicide degradation by soil inoculation techniques (2,4). On a Hillsdale sandy loam with a previously established pH range, microbial degradation of metribuzin [4-amino-6-£mbutyl-3-(methylthio)-tfs-triazin-5(4H)-one] increased with in creasing pH (5).…”

Free radicals in electron donor‐acceptor reactions between a soil humic acid and photosynthesis inhibitor herbicides

“…Previously dicussed experimental results, together with the last considerations, suggest the hypothesis that chemical reactions between these herbicides and humic compounds in soil may simulate analogous biological processes in chloroplasts, on the basis of similar electron donor-acceptor reactions involving free radicals. Such mechanisms have been already considered feasible for the chemical decomposition of amitrole, whose heterocyclic ring is readily susceptible to attack initiated by soil free radicals ( Kaufmann et al, 1968), that may behave similarly to natural flavins and flavoproteins or to artifical free radical generating systems investigated in culture medium and in plants ( Castelfranco and Brown, 1963;Schindfer et al, 1976).…”

Problems Associated with the Use of Azide as an Inhibitor of Microbial Activity in Soil

“…Since during long incubations it is often difficult to prevent reinfection of heat-, radiation-, or chemosterilized soil samples, many investigators prefer to use metabolic inhibitors. Among these, NaN3 (or KN3) and HgCl2 are employed most frequently (1, 5,6,8,12). It is imiportant to recognize that sterilization or metabolic inhibitors may influence soil chemistry in subtle and unintended ways (5,8,14), thus complicating the interpretation of the results obtained.…”

“…Among these, NaN3 (or KN3) and HgCl2 are employed most frequently (1, 5,6,8,12). It is imiportant to recognize that sterilization or metabolic inhibitors may influence soil chemistry in subtle and unintended ways (5,8,14), thus complicating the interpretation of the results obtained. The high absorption and detoxification capacity of soil necessitate the application of metabolic inhibitors at high rates, and the suppression of microbial activity is rarely complete.…”