Herbicide Phytotoxicity as Affected by Selected Properties of North Carolina Soils

Preemergence applications of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine], chloramben (3-amino-2,5-dichlorobenzoic acid), fluometuron [1,1-dimethyl-3-(α,α,α-trifluro- m -tolyl)urea], propachlor (3-chloro- N -isopropylacetanilide), and trifluralin (α,α,α-trifluro-2,6-dinitro- N , N -dipropyl- p -toluidine) were compared in 10 North Carolina soils and the relationship of activity to soil physical and chemical properties appraised. Oats ( Avena sativa L. ‘Carolee’) were used as the indicator plant in bioassays under greenhouse conditions. Fifteen soil properties were measured and correlated with herbicide I 50 (50% fresh weight inhibition) values. Organic matter was the soil variable most highly correlated with herbicide phytotoxicity. There was an inverse relationship between herbicide water solubility and inactivation by organic matter. Volume weight determinations and water holding capacity values (0.1 bar) provided relatively good estimates of soil organic matter contents, but were not as highly related to herbicide activity as organic matter content.