Water-Soil-Plant Interactions with Terbacil

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Abstract
The phytotoxicity of terbacil (3-tert-butyl-5-chloro-6-methyluracil) is not closely correlated with the amount applied, the amount in available soil solution, or the concentration in available soil solution since soil type has a pronounced effect on the levels necessary for phytotoxicity. About 19 times more terbacil was needed in a Chalmers silty clay loam (24% organic matter) than in a Bloomfield fine sand (0.3% organic matter) to cause a 30% control of sorghum (Sorghum biclor(L.) Moench ‘R.S. 610’). However, the Bloomfield fine sand required twice as great a concentration of terbacil in the soil solution as the Chalmers silty clay loam (0.314 μg/ml versus 0.157 μg/ml). The total adsorption of terbacil in the latter soil decreased 4.5 fold when the water: soil ratio was increased from 0.6:1 (approximately field capacity) to 32:1, but the ratio of the concentration adsorbed: concentration in the soil solution did not vary appreciably.