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. 1990. Soil persistence of thiameturon (DPX M6316) and phytotoxicity of the major degradation product. Can. J. Soil Sci.70: [485][486][487][488][489][490][491].The persistence of the herbicidal ester 1r4C)thiameturon was studied at different temperature and moisture conditions in three Saskatchewan soils. [n all soils at 20"C and 85% field capacity, the (raC)ester underwent rapid hydrolysis to 1r4C;thiameturon acid. The hydrolysis was over 85% complete in 1 week, and more than 95% complete after 2 wk. The soil degradation of 1r4C;thiameturon acid was considerably slower than that of the parent eiter. Transformation of 1r4C;thiameturon to acid in all soils at85% freld capacity was temperature dependent, being slowest at 10oC, and fastest at 30oC. Conversion to the acid was also moisture dependent. There was no hydrolysis in air-dry soils after 10 wk. At 5O% freld capacity 22% of the ester remained after I wk, and at held capacity less than 27o of the applied ester was recoverable after I wk.Soils treated with thiameturon acid at rates up to 500 pg g -' exhibited no phytotoxicity to canola, lentil, or sugarbeet seedlings. [(a-methoxy-6-methyl-1,3,5-trol of a wide range of broadleaf weeds in triazin-2-yl)amino I carbonyl I amino I cereal crops. sulfonyl l-2-thiophenecarboxylic acid) Thiameturon is non-volatile, possesses a Cissociation constant (pK") of 4.0 in water at 25"C, and at the same temperature has 485 Can.

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