Sorption of Atrazine, Terbutryn, and GS-14254 on Natural and Lime-Amended Soils

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Abstract
Adsorption of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine], and GS-14254 [2-(sec-butylamino)-4-(ethylamino)-6-methoxy-s-triazine] decreased on natural and limed soils as the soil pH increased to pH 8. More reduction in adsorption occurred with GS-14254 than with the other two herbicides. Increased toxicity to barley from GS-14254 was proportional to decreased adsorption by soils. Adsorption-desorption studies with Chehalis sandy loam (Cumulic Ultic Haploxeroll) indicated that extent and strength of adsorption were equivalent for GS-14254 (pKa 4.36) and terbutryn (pKa 4.32) at a soil pH of 5.20. Two soils, Boyce silt loam (pH 9.6, Cumulic Haplaquoll) and Crooked silt loam (pH 8.5, Xerolic Durorthid), adsorbed thes-triazines readily in contrast to the soils below pH 8. The high adsorption values were substantiated by the GR5 0values on barley for atrazine and terbutryn, 10.2 and 13.2 kg ai/ha, respectively.