Behavior of ¹⁴C‐Atrazine in Argentinean Topsoils under Different Cropping Managements

Abstract

Atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) behavior was studied in four surface soils during incubations in laboratory conditions. Soils were chosen in relation to their cropping management (tillage and no tillage) and crop rotation system (continuous soybean [Glycine mar (L.) Merr.] and maize (Zea mays L.)-soybean rotation). A natural soil under brushwood was sampled as a reference. Atrazine use in field conditions was associated with maize cropping, thus only one soil received atrazine every other year. Atrazine behavior was characterized through the balance of 14C-U-ring atrazine radioactivity among the mineralized fraction, the extractable fraction, and the nonextractable bound residues. Soil organic matter capacity to form bound residues was characterized using soil size fractionation. Accelerated atrazine mineralization was only observed in the soil receiving atrazine in field conditions. Atrazine application every other year was enough to develop a microflora adapted to triazine ring mineralization. Bound residue formation was rapid and increased with soil organic matter content. The coarsest soil size fractions (2000-200 and 200-50 microm) containing the nonhumified organic matter presented the highest capacity to form bound residues. No effect of tillage system was observed, probably because of the uniform sampling depth at 20 cm, hiding the stratification pattern of soil organic matter in non-tilled soils.

Mineralization of 14C-atrazine in an entic haplustoll as affected by selected winter weed control strategies

“…4). The coarsest fraction had a high capacity to form non-extractable atrazine residues (Barriuso and Koskinen, 1996;Hang et al, 2003). The results of this work indicate that SOM of the coarsest fraction would play a dual role on atrazine retention and on mineralization of the available atrazine.…”

“…In previous work, differences by tillage system on atrazine mineralization in 0-20 cm soil depths were not observed (Hang et al, 2003). Therefore, we hypothesized that due to the strong stratification of SOM under no-tillage systems, soil sampling should be done and atrazine behaviour studied according to the stratification pattern of SOM.…”

“…It has been proven that previous atrazine applications stimulate the development of a soil microbial community capable of using atrazine as a source of C, N, and energy (Barriuso and Houot, 1996). Atrazine mineralization can be !50% in periods lower than 28 d during laboratory incubations (Hang et al, 2003). Secondary factors, such as pH, organic C content or cationic exchange capacity, may stimulate or reduce atrazine mineralization (Sparling et al, 1998;Yassir et al, 1999;Houot et al, 2000).…”

Evidence for cross‐adaptation between s‐triazine herbicides resulting in reduced efficacy under field conditions

“…However, in 1995, laboratories isolated bacteria able to catabolize atrazine, a highly substituted s ‐triazine herbicide 6, 7. Since this discovery, enhanced atrazine degradation has been reported for agricultural soils in Argentina, Belgium, Canada, France and the United States 8–17. Moreover, a complete metabolic pathway describing the rapid catabolism of atrazine by bacteria has been elucidated (Fig.…”

Agronomic and environmental implications of enhanceds-triazine degradation

“…Error bars above and below the box indicate the 90th and 10th percentile, and solid dots indicate outliers. The number of independent observations is 14 for non‐adapted soils and 84 for s ‐triazine‐adapted soils 11, 82, 84, 85, 91, 104, 105, 107, 108, 125, 158…”