DEGRADATION OF ATRAZINE IN 2 SOILS AS A FUNCTION OF CONCENTRATION

Dissipation of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s- tri azine) in a Webster clay loam soil (fine loamy, mixed, mesic Typic Hap laquoll), and Estherville sandy loam (sandy, mixed, mesic typic Haplud oll) was determined over a concentration range of 5 to 5000 mg kg(-1) in field and laboratory experiments. Over the first 6 mo in the clay l oam soil, the persistence of atrazine (based on percent of applied) wa s greater for the high-rate treatments than the low-rate treatments. H owever, in the laboratory, there was no effect of concentration on dis sipation; the amount of atrazine degraded increased proportionally wit h the increase of concentration. In the sandy loam, persistence was gr eater at high concentration in both field and laboratory studies. Mine ralization was the most important pathway for the dissipation of atraz ine at all concentrations in the clay loam soil and from 5 to 500 mg k g(-1) in the sandy loam. It was postulated that soil microorganisms we re able to use the N or C from the s-triazine ring. Atrazine at 500 an d 5000 mg kg(-1) may have increased soil microbial growth and activity and thus increased the degradation of atrazine based on the increase in soil respiration in the clay loam soil. Degradation pathways in bot h soils apparently were not influenced by concentration. Ring cleavage and hydrolysis were the major metabolic pathways in both soils, with dealkylation of less importance. Addition of a dairy manure amendment increased the rate of atrazine mineralization, while corn meal decreas ed and (NH)(2)HPO4 amendments prevented mineralization.