Effet de l’herbicide atrazine sur la respiration et l’ammonification de l’azote organique dans un sol agricole au cours d’une incubation

Abstract

The importance of soil microflora and fauna in the breakdown of organic matter and nutrient release for plant growth is well recognized. However, the use of pesticides can affect soil bioactivity in a variety of ways. A long-term incubation laboratory experiment was performed to study the impact of the herbicide atrazine (commercial formulation) on soil respiration and arginine ammonification. The incubation time was lower than the half-life time for atrazine: this allows the presence of significant amounts of residual atrazine in soil throughout the incubation period. Atrazine induced a marked stimulation of cumulative CO2 evolution and the results were analyzed to fit a first-order degradation model for soil organic carbon. In the presence of various atrazine application rates (from 1 to 5 times the agricultural rate), the soil mineralizable carbon content was found to be 1.7 and 1.4 times higher than that of untreated soil. During the incubation, a marked temporal variability occurred in the arginine ammonification rate. Atrazine induced a decrease in ammonification rate, in comparison to the one obtained for the untreated soil. The ammonification rate varied little for atrazine applications greater than three times the agricultural rate, and for incubation times greater than 40 d. The characterization of the relation between the soil CO2 production rate (for 1 or 2 wk) and the ammonification rate (for 3 h) was obtained as a function of incubation time intervals by applying linear regression functions. Results showed that these variables are not significantly related. Key words: Bioactivity, atrazine, respiration, arginine ammonification, agricultural soil