Sorption and desorption of pendimethalin alone and mixed with adjuvant in soil and sugarcane straw

Sugarcane straw may work as a physical barrier for pre-emergent herbicides and interact with their molecules, increasing sorption process. Adjuvants may change herbicides dynamics in the environment and improve their efficiency for weed control. The objective of this work was to evaluate sorption and desorption of pendimethalin alone and in mixture with adjuvant in soil and sugarcane straw. Sorption experiments were performed using pendimethalin alone and in mixture with vegetable oil with herbicide solution concentrations ranging between 2.5 and 40 μg mL^-1 for both conditions. Sorption distribution coefficient (K_d) for soil was 18.48 mL g^-1 using pendimethalin alone. K_d value was not determined when pendimethalin was in mixture with adjuvant due to the complete retention of the herbicide in the soil regardless of the initial aqueous phase concentration. Sugarcane straw sorption experiment had K_d values corresponding to 355.52 and 27.24 mL g^-1 for pendimethalin alone and in mixture with adjuvant, respectively, indicating the addition of vegetable oil may significantly decrease pendimethalin retention in the straw and could improve weed control. Besides all desorption coefficients were higher than the respective sorption coefficients, which means that the sorption process may be considered irreversible.