Effects of farming practices on end-of-paddock run-off water quality in the Central region

Results from end-of-paddock run-off water quality monitoring conducted in the Central region are presented. By measuring nutrient and pesticide concentrations in run-off leaving the paddocks, we aimed to identify farming practices with reduced environmental footprints. This knowledge can be used by growers and advisors to select farming practices that are beneficial for the environment, specifically local waterways and the Great Barrier Reef lagoon. Six trial sites were established between 2020 and 2022. Each trial was designed as a strip trial, with treatments replicated two to three times. At each site, nutrient and pesticide concentrations in run-off were monitored over one wet season. Run-off from liquid imidacloprid applied to the correct label depth (100–125 mm) was less than from liquid imidacloprid applied at half of the recommended depth. The concentration of imidacloprid in run-off across the trial sites where the imidacloprid had been applied to best practice varied considerably. There were no significant differences between the run-off losses for surface-applied dunder, sub-surface-applied granular fertiliser and a sub-surface-applied liquid fertiliser. Run-off losses of imidacloprid, isoxaflutole, metribuzin and DIN were not significantly different between treatments with and without inter-row cultivation using an aerator. Banded mill mud and mill mud/ash treatments increased amicarbazone, isoxaflutole and imidacloprid concentrations in surface run-off compared to where no mill mud products had been applied. Trial data also validated established knowledge on herbicide loss behaviour such as highest loss via run-off occurs in the first run-off event, and/or when run-off occurs in the first 48 h after application, and the benefits of low mobility active ingredients in high-risk periods.