Atrazine behaviour in the different pedological horizons of two Argentinean non-till soil profiles

Summary Atrazine behaviour was investigated in the different pedological horizons from profiles of two non-tilled soils, a Typic Argiustoll and an Entic Haplustoll from the Argentinean pampas. As atrazine use in field conditions was associated with maize cropping, only one type of soil received atrazine every other year. Atrazine behaviour was characterized through the balance of 14C-U-ring atrazine radioactivity among the mineralized fraction, the extractable fraction and the non-extractable bound residues. The composition of the extractable fraction was characterized. Atrazine mineralization was the main dissipation mechanism in the superficial horizon of the Argiustoll because of microbial adaptation after repeated atrazine applications. In contrast, little atrazine mineralization was found in the Haplustoll profile, and it decreased with depth. The capacity of the soil organic matter to form bound residues was characterized using soil-size fractionation. Atrazine-bound residues depended on the soil organic matter content and the size of the fraction. Organic matter in the largest size fractions had a higher capacity to form atrazine-bound residues. In the Argiustoll profile, the atrazine degradation capacity decreased in the subsurface horizons (Bt1 and Bt2), where a large part of bound residues were formed. The deepest horizon (BC) of this profile had a high capacity to degrade atrazine reaching this horizon after a lag period. In the Haplustoll profile, atrazine mineralization and bound residue formation followed the organic carbon mineralization pattern.