Burial and subsequent growth of rigid ryegrass (Lolium rigidum) and ripgut brome (Bromus diandrus) following strategic deep tillage

Abstract

Soil amelioration via strategic deep tillage is occasionally utilised within the conservation tillage systems to alleviate soil constraints, but its impact on weed seed burial and subsequent growth within the agronomic system is poorly understood. This study assessed the effects of different strategic deep tillage practices, including soil loosening (deep ripping), soil mixing (rotary spading), or soil inversion (mouldboard plough), on weed seed burial and subsequent weed growth, compared to a no-till control. The tillage practices were applied in 2019 at Yerecoin and Darkan, Western Australia, and data on weed seed burial and growth was collected during the following three-year winter crop rotation (2019–2021). Soil inversion buried 89% of rigid ryegrass (Lolium rigidum Gaudin) and ripgut brome (Bromus diandrus Roth) seeds to a depth of 10–20 cm at both sites, while soil loosening and mixing left between 31% and 91% of the seeds in the top 0–10 cm of soil, with broad variation between sites. Few seeds were buried beyond 20 cm despite tillage working depths exceeding 30 cm at both sites. Soil inversion reduced the density of L. rigidum to <1 plant m-2 for three years after strategic tillage. Bromus diandrus density was initially reduced to 0-1 plant m-2 by soil inversion but increased to 4 plants m-2 at Yerecoin in 2020 and 147 plants at Darkan in 2021. Soil loosening or mixing did not consistently decrease weed density. The field data was used to parameterize a model, which predicted weed density following strategic tillage with greater accuracy for soil inversion than for loosening or mixing. The findings provide important insights into the effects of strategic deep tillage on weed management in conservational agricultural systems and demonstrate the potential of models for optimising weed management strategies.