SOIL TYPE AND TILLAGE EFFECTS ON SORPTION OF CYANAZINE AND DEGRADATION PRODUCTS

The hydrolytic and dealkylation products of cyanazine have been detect ed in soils, bur the sorption of these products in soil has not been w ell studied. We examined sorption characteristics of five cyanazine de gradation products in relation to cyanazine in Norfolk loamy sand, Tun ica silty clay, and Dundee silt loam soils. Sorption was determined us ing a batch equilibrium method. Air-dried soil (3 g) was shaken in 6 m l of solution containing cyanazine or one of its degradation products for 48 h at 4 C. Five concentrations (2.04 to 54.67 mu mol L-1) of eac h chemical were evaluated. The cyanazine Freundlich coefficient (K-f) ranged from 0.64 in Norfolk soil to 4.75 in Dundee no-tillage (NT) soi l, and was higher in Dundee NT than in Dundee conventional-tillage (CT ) soil. The Freundlich exponent (N) values for cyanazine were less tha n 0.85 in all soils, indicating nonlinearity of the sorption isotherm. In general, cyanazine sorption among the soils increased in the order of Norfolk < < Dundee CT < Tunica < Dundee NT. Cyanazine sorption amo ng the soils was correlated with fine texture and higher organic carbo n content. Sorption of cyanazine degradation products was less than cy anazine sorption in all soils. Isotherms were nonlinear, with sorption decreasing in the order of cyanazine > desmethylpropanenitrile cyanaz ine > hydroxyacid cyanazine > desethyl cyanazine > cyanazine amide > > chloroacid cyanazine. The K-f for chloroacid cyanazine ranged from 0. 21 in Norfolk soil to 0.42 in Dundee NT soil. Sorption patterns of fiv e degradation products among the soils were generally similar to that of cyanazine. Our data indicate that under field conditions, cyanazine degradation products (especially cyanazine amide and chloroacid cyana zine) are more likely to remain in the aqueous phase and thus have a g reater potential to move with water compared to cyanazine.