BENTAZON MOBILITY THROUGH INTACT, UNSATURATED COLUMNS OF CONVENTIONALAND NO-TILL DUNDEE SOIL

Potential ground and surface water contaminants include herbicides tha t are applied postemergence. Although applied to the plant canopy, a p ortion of any application reaches the soil either directly or via subs equent foliar washoff. This study examined the mobility of the posteme rgence herbicide bentazon -methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3 H)-one 2,2 dioxide] through intact columns of Dundee silty clay loam ( fine-silty, mixed, thermic Aeric Ochraqualf) taken from conventional-t ill (CT) and no-till (NT) field plots. Effects of sorption, biodegrada tion, and physical nonequlibrium on bentazon fate and transport were s tudied using miscible displacement experiments. Steady-state, unsatura ted flow was established in 30 cm long by 10 cm in diam. columns, then narrow pulses of Br tracer and C-14-labeled bentazon were applied and displaced through the columns. Once bentazon pulses were eluted, the columns were sectioned and soil extracted for bentazon and metabolites . Despite development of bound residue typical Of bentazon degradation , HPLC analysis gave no evidence of bentazon metabolites in solution. preferential dow occurred in all soil columns and was well-described u sing a two-region, mobile-immobile water model Use of hatch sorption a nd degradation data)ed to predictions of bentazon mobility and residua l C-14 in the soil columns that were generally consistent with the exp erimental data. Attempts to ht the transport data using different degr adation rate constants for conducting and nonconducting regions offere d no better description of the data than use of single rate constants.