SOIL ORGANIC MATTER, MOISTURE, AND TEMPERATURE: EFFECT ON WILD OATS CONTROL WITH TRIFLURALIN

Abstract

The effect of soil organic matter (OM), clay content, temperature, and soil moisture on dose levels of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) required for 90% control of wild oats (Avena fatua L.) was assessed in growth chamber experiments. In the first experiment, where soil moisture was constant, variation in soil OM accounted for 94% of the variability in trifluralin dose rates required for 90% reduction in fresh weight of wild oats (GR90) whereas clay content and temperature had no significant effect. In a second experiment, where temperature was constant, required dose rates were slightly higher at low and high moisture levels than at intermediate levels. Variation in OM explained 80% of the variability in GR90 while the inclusion of moisture and (moisture)2 terms in the multiple regression analysis explained an additional 7% of the variability. The results indicate that trifluralin efficacy was primarily related to OM content and that current recommendations for trifluralin could be improved if based on this parameter. An even more accurate trifluralin dose could be predicted from OM content and soil moisture content but the improvement in efficacy would be slight. Soil OM content determined the amount of trifluralin, dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), and fluchloralin [N(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)-aniline] adsorbed to soil. This suggests that dose recommendations and efficacy of dinitramine and fluchloralin could be predicted from OM content.