Effect of tillage practice on the persistence of atrazine in two contrasting soils in northern New South Wales

Abstract

Grain sorghum was sown at 2 sites at Tamworth in northern New South Wales in 1980 in order to examine the influence of fallow tillage practices and post harvest cultivation on the persistence of atrazine.

In a non-cracking red clay (pH 5.7) atrazine (3.2 kg/ha) was applied both to the sorghum fallow and at sowing (1.8 kg/ha). The concentration of carryover atrazine 3 months after sorghum harvest was 0.11 µg/g in the 0-5 cm mil layer and 0.06 µg/g in the 5-15 cm layer. By contrast, the same treatment resulted in 0.61 and 0.52 µg/g in the 0-5 and 5-15 cm zones of a grey clay (pH 7.5).

Cultivation after the sorghum was harvested reduced the atrazine residue in the surface soil (0-5 cm) by 20-40%, depending on the initial rate of application. There was no associated increase in the 5-15 cm zone. Despite the reduction in the amount of atrazine residue, cultivation increased the severity of atrazine injury to wheat sown at the grey clay site. There was no evidence of phytotoxicity at the red clay site.