POSTGRADUATE Yaseen Khalil, from The University of WA’s (UWA) School of Agriculture and Environment presented the findings of his thesis, on interaction of pre-emergent herbicides and crop residues in WA’s no-tillage systems, at the Institute of Agriculture’s Frontiers in Agriculture showcase recently.
Mr Khalil’s aim was to determine the effects of rainfall amounts, intensity and timing on leaching herbicides from crop residue.
He also studied the effect of how much crop residue is present and how its moisture content can impact herbicide leaching.
The three main herbicides studied were trifluralin, pyroxasulfone and prosulfocarb, with pyroxasulfone proving most effective, followed by prosulfocarb, then trifluralin.
After a series of experiments were carried out to investigate how much herbicide was intercepted by crop residue and the effects of rainfall, Mr Khalil come to the following conclusions.
“Some of the herbicide leached from the residue with as little as five millimetres of rainfall, although higher rainfall amounts generally leached more herbicide from the crop residue,” he said.
“The sooner the rainfall occurred, the greater the amount of herbicide leached, although there was no difference between rainfall intensities.”
Mr Khalil also looked into the effects of the crop residue, including if the straw was laying flat or still standing. His experiments demonstrated that standing crop residue was less likely to intercept herbicides and stop leaching than if it was laying over the ground.
“Rainfall was very effective in leaching pyroxasulfone from the residue, even in heavy residues of four tonne per hectare, when rainfall occurred up to 14 days after application,” he said. However the rainfall was least effective in leaching trifluralin from the residue, even when rainfall occurred one day after application.
Mr Khalil also tested different types of crop residue and found that barley and wheat residue intercepted significantly more herbicide compared to canola, chickpeas and lupin residue.
This finding was proven with all three different herbicides.
Mr Khalil’s final conclusion was farmers should try to keep their residue standing and also apply pyroxasulfone which was the most effective with crop residue out of the three tested.
Also, less herbicide was leached after the rainfall if the chemicals were applied to initially wet residue.