Closing the knowledge gap on the impact of herbicide residues in soils

Growing up in Myanmar, Soil CRC PhD student Win Win Pyone developed an interest in agriculture early in life. Armed with a thirst for knowledge and a desire to apply that knowledge to make a positive impact, she decided to take on tertiary studies in Agriculture both at home and abroad.

“I completed a Bachelor of Agricultural Sciences in Myanmar in 2004 and pursued my Master’s degree in Japan in 2012, so completing a PhD focused on Agricultural Sciences in Australia seemed like a natural progression,” Win Win said.

“I’m inspired by the challenge of finding sustainable solutions in agriculture, particularly through research that addresses environmental issues.

“I’m passionate about work that not only improves crop production but also benefits the environment, supporting healthier ecosystems and communities,” she enthused.

Win Win moved to Western Australia to complete her PhD at Murdoch University, working with Soil CRC researchers as part of our ‘Improved management of herbicide residues in soil’ project (4.2.001).

“My research explored the effects of lingering herbicide residues on grain crops, especially in sandy soils typical for winter grain crops in Australia.

“The aim was to help close the knowledge gap regarding phytotoxicity thresholds for herbicide residues, particularly focusing on diuron, a herbicide used to control broadleaved and grass weeds,” she explained.

Using glasshouse studies, Win Win applied various methods to assess the phytotoxic effects. Key methods included glasshouse bioassays, dose-response experiments, and nonlinear regression modelling to determine effective doses (ED₅₀) of diuron and other herbicides that result in a 50% reduction in crop growth.

“I evaluated diuron’s impact on canola, wheat, and chickpea, observing that canola was especially sensitive. I also investigated soil-specific responses by comparing loamy sand (a mixture of sand, silt and clay) and inert sand; loamy sand showed reduced toxicity due to its higher organic matter and cation exchange capacity (its ability to hold positively charged ions), which limited diuron’s bioavailability,” she said.

In a broader assessment, Win Win tested four herbicides (clopyralid, trifluralin, pyroxasulfone, and propyzamide) on six winter grain crops (canola, chickpeas, field peas, lentils, lupins and wheat).

“I found that lentils were highly sensitive to clopyralid, and wheat was particularly affected by propyzamide and trifluralin. I also examined the combined effects of diuron, diflufenican, and trifluralin, revealing additive, antagonistic, and synergistic interactions, with diuron showing strong toxicity on canola in combination.”

Win Win also analysed soil properties like organic carbon (OC) and cation exchange capacity (CEC) to understand their impact on diuron’s toxicity. Higher OC and CEC levels correlated with reduced phytotoxicity, and OC emerged as the best predictor, where higher OC soils needed more diuron to reach toxic levels.

“These findings indicate that certain herbicides pose phytotoxic risks to non-target crops at levels below standard application rates, especially in soils with lower organic carbon. Therefore, soil properties significantly affect herbicide bioavailability, and understanding these dynamics is crucial to managing herbicide carryover in crop systems.”

The results of Win Win’s research help to build our understanding of herbicide residues and their effects. This new knowledge will assist farmers, agronomists and extension officers identify a suitable time for crop sowing, crop choice, and herbicide management to be able to upgrade soil and crop performance with minimal harmful effects of residual herbicides in soils.

“My thesis contributes significantly to weed management in Australian grain production systems by investigating the crop and environmental impacts of soil-borne herbicide residues,” Win Win said.

“This research focused on optimising the use of pre-emergent herbicides amid rising resistance to post-emergent alternatives. It provides critical insights into managing herbicide phytotoxicity and minimising negative effects on crops, offering valuable guidance for sustainable agricultural practices in Australia’s cropping systems.”

When asked what she enjoyed most about her PhD experience, Win Win said she relished working on a project with practical benefits for farmers and the agriculture industry, collaborating with supportive supervisors and like-minded researchers, and the hands-on glasshouse work that brought her research to life.

“The support from my mentors and peers made the challenges rewarding, and knowing my work could help solve real agricultural issues added a deep sense of purpose to my PhD experience.”

With her PhD journey coming to an end, Win Win said she plans to work in agricultural research, focusing on sustainable crop management and herbicide impact.

“I’m eager to collaborate on innovations that support farmers and sustainable practices into the future,” she said.

Keen to collaborate or talk with Win Win? Connect via LinkedIn.