The fate of herbicide residues in soil – why it matters and what research is telling us

Dr Mick Rose from NSW Department of Primary Industries (now Southern Cross University) and his team have been investigating the breakdown of different herbicides across a range of soil types and rainfall zones.

During the fallow or in-crop season, there are often several applications of herbicide, and some residues may still be present on or near the soil surface when it is time to plant the next crop. Particularly in dry years, residues may even carry over from the crop prior to the fallow.

Mick outlines the effect these residues may have on soil microbial activity and on the establishment and growth of crops following the fallow, even after the plant back period.

Topics covered include:

• Herbicide residue risk
• What drives herbicide dissipation?
• Herbicide persistence in soil:
  • Moisture, temperature, organic matter
  • Microbial activity important for degradation
• Herbicide sorption – binding to soil
• Case study: trifluralin persistence in Vic Wimmera/Mallee
• Case study: clopyralid persistence in Eyre Peninsula, SA
• Case study: residues in peanut soil, Qld

Speakers

Mick Rose, Soil researcher, NSW Department of Primary Industries

Dr Mick Rose is interested in the interactions between plants, microorganisms and their environment and how agronomic management practices influence these interactions. Mick undertook his PhD at the University of Sydney through an Australian Cotton CRC scholarship, exploring the role of wetland plants and microorganisms in improving water quality on cotton farms. Mick has since conducted research on plant growth-promoting biofertilisers in Vietnam; abiotic stress tolerance in rice in Japan and organic amendments for soil health and plant productivity in Victoria, Australia. For the last five years, Mick has been working on a variety of projects researching pesticide fate and the potential impacts of pesticides on soil biological processes, crop health and the wider environment. He is also interested in ways to measure, monitor and improve soil health.

Greg Condon, WeedSmart southern extension agronomist

Greg is the WeedSmart southern extension agronomist (Vic and NSW) and is based in Junee, NSW. He runs Grassroots Agronomy with his wife Kirrily Condon. Greg works with growers and industry groups and is passionate about profitable farming systems. Connecting innovative growers with agronomists, stakeholders and researchers is a major focus of Greg’s extension role.

Relevant resources

How can I be certain that herbicide residues in the soil have fully degraded at planting?