Farm Table says:
Rainfall affects leaching of pre-emergent herbicide from wheat residue into the soil
What is the problem?
No tillage farming in wheat crops has become more popular, but the crop residue left on the surface of the soil prevents some pre-emergent herbicides from being able to reach the soil surface, rendering the herbicide ineffective.
Researchers from the University of Western Australia looked at the effect of rainfall timing, amount and intensity; and the effect of single and multiple rainfall events on the leaching of prosulfocarb, pyroxasulfone and trifluralin from wheat stubble.
What did the research involve?
They performed two experiments in controlled conditions, using typical soil from the WA wheat belt and crop residue collected from the same wheat farm:
- Four simulated rainfall amounts (0, 5, 10, and 20 mm)
Three intensities (5, 10, and 20 mm h–1)
Five application times (immediately after spraying herbicide, 6 hours, 1 day, 7 days , and 14 days after spraying).
- 20 mm of simulated rainfall was applied at 10 mm/hour in either 4 × 5 mm rainfall events over two days, 2 × 10 mm rainfall events over one day, or a single 20 mm rainfall event, with a no-rainfall control treatment.
Bioassays were used to assess the herbicide activity/availability in the soil and remaining on the residue, using cucumber (Cucumis sativus L.) and Italian ryegrass (Lolium multiflorum Lam.) as indicator plants.
What were the key findings?
Although the rainfall intensity showed no effect, high rainfall volumes shortly after herbicide application caused most of the herbicides to leach from the crop residue into the soil.
Pyroxasulfone leached most easily from the crop residue compared to the other herbicides and was still chemically active and able to be leached from the stubble after 14 days. While Trifluralin on the other hand, becomes volatised after 48 hours of no rain and leached the least. Prosulfocarb displayed intermediary responses to leaching and was chemically actively for up to 7 days. After this time period of no rain and sitting on the stubble the herbicide loses efficiency.
This research shows that in no-till systems with dense crop residue present on the soil surface, herbicides such as pyroxasulfone that leach easily from the stubble should be considered.
This paper was summarised by Mia Courtney (Agricultural Sciences Student – La Trobe University) and reviewed by Nickala Best (PhD Student – La Trobe University). Learn more about Mia and Nickala here.