Fate of atrazine in soybean (Glycine max L.) and corn (Zea mays L.) succession in Brazilian subtropical conditions

This work aimed to evaluate the distribution of atrazine via surface runoff, leaching, and retention in a Rhodic Ferralsol and to analyze the effect of a succession of corn and soybean crops in Brazilian subtropical edaphoclimatic conditions on the distribution of this herbicide. The mobility of atrazine was evaluated using a drainage lysimeter under conditions of intensely simulated precipitation, carried out 24 h and 48 h after a single herbicide application at 17 days after corn emergence. Surface runoff and leaching were sampled during the rainfall simulations at intervals of 5 min until completing 1 h. Corn foliar analyses were carried out to measure the residual amounts of atrazine. In addition, laboratory studies of sorption (equilibrium and thermodynamics) and dissipation were carried out to understand the dynamics of atrazine in the soil. Freundlich's non-linear isotherms presented an excellent fit in the description of atrazine sorption in a Rhodic Ferralsol. The high content of organic matter in the soil and the temperature variation directly influences the retention of atrazine in the soil. The halflife (t1/2) of atrazine in soil under controlled conditions indicates a non-persistent pesticide, with 14.44 days. However, the herbicide can persist in deep soil layers for more than 93 days after spraying. When high-intensity rainfall occurs 24 h after application, large proportions of atrazine are lost by runoff within the first 20 min of rain. At the same time, significantly inferior losses are observed when rainfall occurs 48 h after spraying. Highintensity rainfall within 24 h of atrazine application leads to substantial losses, causing an approximate 84% reduction in its concentration in corn leaves and a 94% reduction in soil. Conservationist agronomic practices that protect the soil, especially during the initial periods of corn cultivation, are essential to reduce atrazine losses by runoff or leaching. In addition, increasing the concentration of organic matter in the soil can be extremely promising in increasing the retention of this pesticide to soil colloids, preventing its loss in soils with a low content of clay minerals.