Strategic deep tillage can significantly improve soil properties, but these improvements can present challenges for weed management.

Amelioration practices not only benefit crop performance but can also, unfortunately, improve the performance of weeds.

Dr Arslan Peerzada, a research scientist at the Department of Primary Industries and Regional Development, has been investigating this issue with a team in a major GRDC investment.

“In the first year after amelioration, we observed inadequate weed control and these findings emphasise the need for tailored weed management practices that extend beyond relying on pre-emergent herbicides alone,” Dr Peerzada says.

“These integrated approaches would include in-crop herbicides, herbicide-tolerant crops and harvest weed seed control. The objective is clear: to minimise weed seed production in the first year following strategic deep tillage, thus maximising the long-term benefits of soil amelioration programs.”

Underpinning Dr Peerzada’s recommendations are insights from studies investigating weed response to soil constraints, weed seed burial dynamics, and evaluation of pre-emergent herbicides’ efficacy in the first year after strategic deep tillage.

The impact of amelioration practices on weed growth, emergence patterns and competitiveness are undeniable, but it is variable across different weed species. For example, wild radish thrives with increased growth and competitiveness regardless of improved growing conditions for the crop.

“Soil inversion was observed to effectively suppress small-seeded weeds such as annual ryegrass, but not large-seeded weeds such as great brome or wild radish seed in pods – which are both economically damaging weed species for WA growers.

“Under ideal conditions almost 100 per cent weed seed burial can be achieved with soil inversion. However, depending on the soil moisture levels, machinery set-up and tillage depth, the amelioration treatment can have variable effects on weed seed distribution. It may leave a significant number of weed seeds at the surface or only within 10 centimetres of the surface. This is an ideal depth for many weed species to emerge from.”

Shallow burial (in other words, similar to an ‘autumn tickle’) by deep ripping in particular can be conducive to weed seed germination, Dr Peerzada says.

“Examining a range of pre-emergent herbicides for their efficacy in ameliorated soils, we found many were unable to control the weeds, and wild radish was a significant problem as it continued to persist.”

Dr Peerzada concludes that successful weed management in ameliorated soils requires a thorough understanding of the diverse effects of deep tillage practices on weed ecology, seed burial patterns and herbicide performance.

More information: Dr Arslan Peerzada, 08 9699 2133, arslan.peerzada@dpird.wa.gov.au