Chlorsulfuron residues are not accumulating in soils of southern Queensland

Abstract

Chlorsulfuron persistence was measured in soils (to a depth of 150 cm) at 4 sites in the winter cereal region of southern Queensland. The residual herbicide had been applied 6-14 times in the previous 7-14 years. Residues here measured using a bioassay based on suppression of root growth of maize (Zea mays cv. GH5010). Less than 3% of the total applied chlorsulfuron (96-210 g a.i./ha) was detected 6-12 months after the last application, and residues were <0.7 ng/g soil in the surface 30 cm, and <0.3 ng/g below 30 cm. The limited vertical movement of residues was associated with the herbicide being applied in early winter, several months before leaching rains. Changes in residue concentration with time were also measured at a site in central Queensland, and in a fallow management experiment in southern Queensland. Persistence was greater at the cooler, drier site in southern Queensland than in central Queensland; 4544% compared with 3 4 % of applied dose remained 3 months after application respectively. Stubble retention had no effect on persistence, but tillage during the summer fallow increased persistence slightly. There was no evidence of chlorsulfuron residues accumulating and only limited leaching in these alkaline agricultural soils of southern Queensland. Persistence within a season was influenced by soil and climatic factors.