Sorption-desorption isotherms of diuron alone and in a mixture in soils with different physico-chemical properties

Herbicide mixture is a widely used weed control practice in many agricultural areas. However, interactions between the herbicide mixture and soil may alter the soil dynamics. This research evaluated the effect of the physicochemical properties of the soils in the application of diuron alone and in a mixture with hexazinone, by means of sorption-desorption Freundlich isotherms. 14C-diuron sorption (isolated and mixed) was evaluated by batch equilibration at five concentrations of diuron (0.14, 0.16, 0.19, 0.26 and 0.39 μg mL-1) and hexazinone (0.03, 0.06, 0.13, 0.19 and 0.26 μg mL-1), corresponding to the recommended field dose (D) of D/4, D/2, D, 2×D and 4×D, respectively, in five soils cultivated with sugarcane. The sorption of the diuron applied separately and in mixture presented Freundlich sorption coefficient (Kf) values in the range of 1.47 to 5.08 and 0.59 to 3.77 µmol(1-1/n) L1/n kg-1, respectively. The lowest desorption values were found for Clay-1 soil (72.5% clay), with 6.01 and 5.87% for diuron isolated and blended, respectively. Diuron sorption was slightly higher when applied alone rather than in the herbicide mixture, and this sorption correlated positively with the clay content of the soils, regardless of the application form. The disponibility of diuron improved in mixture of hexazinone in soil, which can increase its absorption and control efficiency; on the other hand, the transport of herbicide can rise. Future researches about the transport, runoff or leaching are required for complete information of the behavior of this mixture of herbicides in soil. Key words: Retention process, sorption kinetics, hysteresis, commercial mixture.