How increasing availabilities of carbon and nitrogen affect atrazine behaviour in soils

The effect of increasing amounts of glucose and mineral N on the behaviour of atrazine was studied in two soils. One had been exposed to atrazine under field conditions (adapted soil), the other had not (nonadapted soil), resulting, respectively, in an accelerated degradation of atrazine in the adapted soil and in a slow degradation of the herbicide in the non-adapted soil. The dissipation of C-14-atrazine via degradation and formation of non-extractable "bound" residues was followed during laboratory incubations in soils supplemented or not with increasing amounts of glucose and mineral N. In both soils, glucose added at rates of up to 16 g C kg(-1) soil did not modify atrazine mineralization but increased the formation of bound residues; this was probably due to the retention of atrazine by the growing microbial biomass. Atrazine dealkylation was enhanced when a large amount of glucose was added. In both soils, the addition of the largest dose of mineral N (2.5 g N kg(-1) soil) decreased atrazine mineralization. The simultaneous addition of glucose and mineral N enhanced their effects. When the largest doses of mineral N and glucose were added, atrazine mineralization stopped in both soils, and the proportion of bound residues increased. Glucose and mineral N additions influenced atrazine mineralization to a greater extent in the adapted soil than in the non-adapted one, as revealed by ANOVA, although glucose addition had a greater effect than N. The competition for space and nutrients between atrazine-degrading microorganisms and the total heterotrophic microflora probably contributed to the decrease in atrazine mineralization.