S. Meyerwindel et al., ON THE RELATION OF HERBICIDE ADSORPTION A ND SOIL ORGANIC FRACTION, Zeitschrift fur Pflanzenernahrung und Bodenkunde, 160(4), 1997, pp. 361-368
Freundlich adsorption isotherms were measured for four herbicides (atr
azine, terbuthylazine, chlorotoluron, isoproturon) and 24 soil horizon
s, which are typical of Schleswig-Holstein, northern Germany. The rela
tionship between the adsorption constant (K-Fr) of a chemical and the
fraction of organic carbon (f(OC)) of the soil horizons was evaluated.
Chemical specific K-OC'-values, that are independent of soil organic
carbon fraction varied considerably for each herbicide (CV about 50%);
therefore these values as well as K-OC-values, that are determined by
linear regression of K-Fr and f(OC) should be evaluated critically be
fore application. K-OC'- and K-OC-values derived from experiments show
ed decreasing affinity of the herbicides to soil horizons in the order
terbuthylazine > chlorotoluron > atrazine congruent to isoproturon. C
alculation of K-OC from K-OW or water solubility of each herbicide, ho
wever, led to changes in the above mentioned ranking. Hence, especiall
y K-OW or water solubility based K-OC-values may lead to false conclus
ions concerning chemical mobility. For atrazine, terbuthylazine and is
oproturon Freundlich adsorption constants increased overproportionally
with increasing organic carbon content of soils. The relationships be
tween K-Fr and f(OC) therefore were described better by a non-linear e
quation (second order polynom) than by a linear approach. Contrary, fo
r chlorotoluron a linear relation between K-Fr and f(OC) holds at leas
t for the range of f(OC) investigated in this study.