Dependence of atrazine degradation on C and N availability in adapted and non-adapted soils

Atrazine degradation in soil was affected by microbial adaptation and C and N availability. Accelerated atrazine mineralization was observed after repeated applications to a soil under continuous maize (adapted soil) while atrazine mineralization remained slow in an adjacent soil under wheat that had never received atrazine (non-adapted soil). Carbon-14 atrazine degradation and formation of unextractable 'bound' residues were determined during laboratory incubations in soil alone or amended with different organic amendments (OAs) and N sources. The OAs varied from readily biodegradable (glucose) to more slowly mineralizable (cellulose and straw) and humified organic matter (compost). The N forms included mineral (NH4NO3, (NH4)(2)SO4 and Ca(NO3)(2)) and organic forms (adenine, arginine, albumin, biuret and pyrazine) which varied in N availability. In the adapted soil, OA addition had little effects on atrazine degradation, whereas in the non-adapted soil, it stimulated atrazine dealkylation more than triazine ring mineralization which always remained lower than in the adapted soil. In both soils, mineral N decreased triazine ring mineralization. The depressive effect of the organic N forms on atrazine mineralization increased with their N mineralization rate. Despite its slow N mineralization rate, the addition of biuret greatly decreased atrazine mineralization, possibly because it is one of the last intermediates in atrazine degradation. The proportion of bound residues increased with the total microbial activity after addition of OAs or organic N forms. In conclusion, rapid triazine ring mineralization was dependent on microflora adaptation after repeated atrazine application and was mainly regulated by N availability in soil. (C) 2000 Elsevier Science Ltd. All rights reserved.