Herbicide mixtures affect adsorption processes in soils under sugarcane cultivation

The use of herbicide mixtures has been a common practice in the control of weeds in sugarcane crops. The concern with the interactions between the molecules of different herbicides has been limited to compatibility before application. In this sense, little is known about the interactions between mixed herbicides and the soil. The objectives of this study were to investigate the sorption process of diuron, hexazinone, and sulfometuron-methyl in isolated and mixed conditions to soils under sugarcane cultivation. Kinects and isotherms models were used to understand the behavior of herbicides in the soils. The adsorption time and the sorption capacity of the herbicides had the following order of diuron > hexazinone > sulfometuron-methyl in the dystrophic red Oxisol and diuron > sulfometuron-methyl > hexazinone in the red-yellow Oxisol. Herbicide mixtures reduced the maximum adsorption (qe) in approximate to 50 (diuron), 56 (hexazinone), and 55% (sulfometuron-methyl) compared isolated tests. Also, herbicide mixtures reduced the sorption rate (Kf) 24 (diuron), 89 (hexazinone), and 66% (sulfometuron-methyl) compared to conditions isolated tests. Desorption process was higher for herbicides when mixed in binary and ternary condition. The sorption and desorption of hexazinone in soils is most affected by mixing with other herbicides. Sulfometuron-methyl promotes greater reduction in the sorption of diuron (approximate to 33%) compared to hexazinone (approximate to 21%). The mixture between diuron, hexazinone, and sulfometuron-methyl increases the availability of these herbicides in the aqueous phase of the soil allowing the use of lower rates in the application compared to isolated applications. Higher availability also indicates a greater potential for environmental contamination via leaching or surface runoff.