Herbicide residues in sandy soils of the Southern region

Authors: Lynne Macdonald¹, Rai Kookana¹, Nigel Wilhelm², Therese McBeath¹, Rick Llewellyn¹

Research Team: Barry Haskins³, Michael Moodie⁴, Adelle Craig¹, Jun Du¹

¹CSIRO, Waite Campus, ²SARDI, Waite Campus, ³AgGrow Agronomy, Griffith, ⁴Mallee Sustainable Farming, Mildura

Funded By: GRDC Sandy Soils CSP000203

Project Title: Increasing production on sandy soils – overcoming constraints to poor water use

Peer Review: Lukas van Zwieten, Mick Rose

Key Words: herbicides, residues, sands, sandy soil

Key Messages

• A study of herbicide residues in sandy soils in the southern low rainfall region found Glyphosate and its breakdown product AMPA at all nine sampled sites.
• The combined residue load (Glyphosate plus AMPA, 0-30 cm) represented between 0.7 and 6.1 typical applications. The majority (~85%) of the herbicide residue was found in the top 10 cm, and was predominantly AMPA (~80%) rather than Glyphosate.
• Little is known of the toxic effects of AMPA and how it may affect root growth and function across different crop species. Identifying threshold levels of AMPA that negatively impact crop productivity would be valuable.
• The study detected Trifluralin (8/9 sites) and 2,4D (4/9 sites) at low concentrations unlikely to be damaging to crops. We did not detect Prosulfocarb, imidazolinones (Imazapic, Imazapyr, Imazamox), Triclopyr, or MCPA. Spray history details are being collated to further understand the Glysphosate results and assess whether non-detection of other herbicide residues is due to infrequent use or to breakdown.