Trifluralin Behavior in Soil. I. Toxicity and Persistence as Related to Organic Matter¹

Abstract

Abstract The incorporation of either the alkali‐extractable colloidal fraction of leonardite or activated charcoal in mineral soils of low organic matter content resulted in increased toxicity to barley and cucumbers from surfaceapplied trifluralin. Linear or nearly linear responses were obtained up to 6.0% O. M. at 41, 43, 81, and/or 93 days after application of treatments. Subsurface application of trifluralin resulted in no increase in toxicity with increasing rates of charcoal at 43 days, but a significant increase was found at 93 days at the 6.0% O. M. level. GR 50 values for O. M. in soil ranged from 4.6 to 11.0 for surfaceapplied trifluralin. Correlation coefficients for reduction in plant growth versus O. M. rates were generally high. It is indicated that the increased trifluralin toxicity with increased organic matter in the soil is due to greater retention (adsorption) of the vapor phase of the herbicide and that this toxicity can persist up to 93 days from application.