Improved management of herbicide residues in soil

The loss of productivity due to herbicide residues as a soil constraint has not been accurately determined due to the complexity and lack of tools to quantify herbicide damage. However, it is thought to be significant, particularly in sandy soils.

Herbicides are a valuable tool for controlling weeds and realising crop yield potential. Currently, herbicide label guidelines are general and unable to account for the combinations of soil types and weather conditions that can affect herbicide persistence in soil. Herbicide residues in soils can limit crop performance if not managed correctly. It is difficult for growers and advisors to know whether herbicide residues will cause issues, because the persistence and behaviour of these residues depends on numerous site-specific factors, including soil and climatic conditions.

Increased weed resistance to herbicides means that many growers are increasing application doses and frequency, increasing the range of herbicides used and importantly, returning to pre-emergent residual herbicides.

Growers need evidence-backed guidance on the site-specific persistence of herbicides to allow for flexible crop selection and avoidance of plant-back damage, and field-validated information on the potential long-term effects of herbicide residues on soil and crop health.

There are currently very few tools to assist growers to determine the level of herbicide residues present, and if they negatively affect soil and crop performance. This project will develop new knowledge and tools to better understand the factors regulating herbicide persistence and bioavailability. This will give farmers an increased confidence in crop choice, timing of sowing and herbicide management to ensure soil and crop performance are not limited by herbicide residues.

The outcome will be that farmers are better informed and equipped to react to variable environmental and soil conditions, which will reduce risk and increase crop diversity, yields and economic returns at a lower environmental cost. Importantly, major losses after planting will be eliminated and farmers will have greater flexibility in crop rotations to further build soil health.