Strategic deep tillage in no-till wheat systems affected soil properties, weed seed burial, and pre-emergent herbicide performance in the first year

Strategic deep tillage in Western Australia (WA) is increasingly being used in continuous no-till (NT) systems to alleviate soil constraints and manage persistent weed seedbanks. This study evaluated the effects of deep ripping, deep mixing, and soil inversion, compared to NT, on soil properties, vertical weed seed distribution (using plastic beads as surrogates), and pre-emergent herbicide efficacy against annual ryegrass ( Lolium rigidum ), great brome ( Bromus diandrus ), and wild radish ( Raphanus raphanistrum ) at Wongan Hills and Merredin, WA. Soil inversion and deep mixing at Wongan Hills substantially altered topsoil properties, reducing total soil organic carbon (SOC) by 18–35% in the topsoil. These practices buried plastic beads below 10 cm, indicating strong weed suppression potential, while deep ripping left more seeds near the surface, resulting in higher weed densities. Pre-emergent herbicide performance was affected by total SOC and soil moisture/rainfall and weed seed burial; at Wongan Hills, tri-allate plus flumioxazin and trifluralin application to dry soil followed by heavy rainfall reduced wheat establishment (−21%) and yield (−41%), whereas adequate rainfall before sowing at Merredin allowed effective weed suppression without crop injury. Soil inversion and deep mixing enhanced weed suppression and soil conditions, increasing wheat grain yield by up to 59% relative to NT, but pre-emergent herbicides along with deep tillage proved insufficient for long-term weed control, particularly when seeds are buried beyond the herbicide-effective zone. These results highlight the importance of site-specific herbicide selection and integrated weed and crop management to maximise the benefits of deep tillage in continuous NT systems, especially in sandy soils with low sorption capacity and variable rainfall.