Adsorption and Efficacy of Trifluralin and Butralin as Influenced by Soil Properties

Significantly higher rates of butralin [4-(1,1-dimethylethyl)- N -(1-methylpropyl)-2,6-dinitrobenzenamine] were required to produce the same level of weed control as trifluralin [2,6-dinitro - N,N -dipropyl-4-(trifluoromethyl) benzenamine] when applied to soybeans [ Glycine max (L.) Merr.] on seven different soils in the field. Higher rates of butralin were also required to control barnyardgrass [ Echinochloa crus-galli (L.) Beauv. ♯ ECHCG] in growth chamber studies. No differences in the extent of soil adsorption of trifluralin and butralin were apparent; therefore, differences in efficacy could not be attributed to differences in soil adsorption. Herbicide rates required for 80% weed control and Freundlich K-values (adsorption capacity indices) were mostly highly correlated with soil organic-matter content and soil surface area as measured by benzyl ethyl ether (BEE) and ethylene glycol monoethyl ether (EGME) on nine soils. Analysis of the organic-matter content of the nine soils by 10 soil testing laboratories resulted in highly significant differences among laboratories.