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1 July 2012 Determination of Thiencarbazone in Soil by Oriental Mustard Root Length Bioassay
Anna M. Szmigielski, Jeff J. Schoenau, Eric N. Johnson, Frederick A. Holm, Ken L. Sapsford
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Using an oriental mustard root length bioassay, thiencarbazone bioavailability and dissipation in five Saskatchewan soils was investigated under laboratory conditions. Thiencarbazone bioavailability was assessed at 0 to 3.9 µg ai kg−1. Thiencarbazone concentrations corresponding to 50% inhibition (I50 values) obtained from dose-response curves varied from 0.56 to 1.71 µg kg−1. Multiple regression analysis indicated that organic carbon content (P  =  0.018) and soil pH (P  =  0.017) predicted thiencarbazone bioavailability. Thiencarbazone dissipation was examined in soils incubated at 23 C and moisture content of 85% field capacity. Thiencarbazone half-lives estimated from dissipation curves were 9 to 50 d, and organic carbon content (P  =  0.002) and soil pH (P  =  0.008) were significant factors affecting thiencarbazone dissipation. Thiencarbazone bioavailability decreases and dissipation rate is slower in Canadian prairie soils of high organic matter content and low soil pH. Because root length of oriental mustard plants also was reduced by ammonium, therefore ammonium-containing or -producing fertilizers can cause false positive results for thiencarbazone soil residues. Canaryseed roots had the same sensitivity to ammonium as oriental mustard roots but were not inhibited by thiencarbazone. Therefore canaryseed root length bioassay was effective in identifying inhibition caused by ammonium toxicity. Use of oriental mustard root and canaryseed root bioassays together can aid in interpreting bioassay results for detection of thiencarbazone residues.

Nomenclature: Thiencarbazone, oriental mustard, Brassica juncea (L.) Czern. ‘Cutlass’; canaryseed, Phalaris canariensis L. ‘CDC Togo’.

Weed Science Society of America
Anna M. Szmigielski, Jeff J. Schoenau, Eric N. Johnson, Frederick A. Holm, and Ken L. Sapsford "Determination of Thiencarbazone in Soil by Oriental Mustard Root Length Bioassay," Weed Science 60(3), 468-473, (1 July 2012).
Received: 15 April 2011; Accepted: 1 December 2011; Published: 1 July 2012
Ammonium toxicity
canaryseed root length bioassay
oriental mustard root length bioassay
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