Laboratory study on leachability of five herbicides in South Australian soils

Norflurazon, oxadiazon, oxyfluorfen, trifluralin and simazine are herbicide s widely used in the vineyards of the Barossa Valley, South Australia. The leaching behaviour of norflurazon, oxadiazon, oxyfluorfen and trifluralin w as investigated on four key soils in the Barossa Valley. Leaching potential on packed soil columns and actual mobility using intact soil columns were investigated. On the packed soil columns, norflurazon was the most leachabl e herbicide. More of the herbicides were detected in the leachates from the sandy soils (Mountadam and Nuriootpa) than from the clayey soils (Lyndoch and Tanunda). Organic matter is generally low in soils in the Barossa regio n. Porosity and saturated conductivity significantly affect herbicide movem ent and in the sandy Mountadam and Nuriootpa soils, the water flux is great er than for the higher clay content Lyndoch and Tanunda soils. Increasing t he time interval between herbicide application and the incidence of "rainfa ll" reduced the amounts of herbicides found in the leachates. The use of in tact soil columns and including simazine for comparison showed that both no rflurazon and simazine were present in the leachates. Simazine was the firs t herbicide to appear in leachates. Sectioning of the intact soil columns a fter leaching clearly demonstrated that norflurazon and simazine reached th e bottom of the soil columns for all soils studied. Greater amounts of norf lurazon were retained in the soil columns compared with simazine. The other herbicides were mostly retained in the initial sections of the soil column s.