Sorption and desorption of diuron and norflurazon in Florida citrus soils

The potential for surface and groundwater contamination of soil applied herbicides is partly dependent on soil properties. Sorption and desorption of diuron and norflurazon were studied in seven soils representative of the southern citrus-belt of Florida using the batch-equilibrium technique. Sorption of herbicides was influenced by soil properties. Sorption coefficients (K _d) ranged from 0.84 to 3.26 mL g^?1 for diuron and 0.63 to 2.20 mL g^?1 for norflurazon indicating weak to moderate binding of herbicides to soil. For norflurazon, K _dwas significantly related to organic C content, soil pH, and cation exchange capacity. For diuron, absence of a significant relationship between K _dand selected soil properties suggests that the soil properties other than those studied may play a role in determining sorption on these soils. Desorption studies showed that higher amounts of diuron and norflurazon was desorbed by water than by 0.5 M CaCl₂. An inverse relationship was apparent between herbicides sorbed and that which was desorbed among the soils studied. The soil which exhibited higher sorption had lower desorption and the soil which exhibited lower sorption had higher desorption.