Influence of Clay and Organic Matter of Rangeland Soils on Tebuthiuron Effectiveness

Abstract

Phytotoxicity of tebuthiuron applied at 0.12, 0.25, or 0.5 ppm to 10 different rangeland soils containing huisache in the greenhouse was inversely related with clay and organic matter contents. However, influences of soil properties were greatest at low herbicide dosages and could be masked by increasing tebuthiuron application rate. For example, tebuthiuron at 1 or 2 ppm killed the huisache after 287 days, regardless of soil, whereas 0.12 or 0.25 ppm killed huisache only when applied to soils with less than 15% clay (these soils contained less than 2.5% organic matter). Potential for tebuthiuron phytotoxicity appears to be greatly diminished in soils containing more than 30% clay. Although the effects of organic matter were confounded with soil clay contents in this study, variations in clay content consistently accounted for a greater proportion of variation in huisache response than did organic matter content.