Weed seed burial and long-term viability following soil inversion

Abstract Strategic soil inversion is advocated as a periodic weed management strategy, typically recommended every 4 to 8 yr if the goal is to delay the evolution of herbicide resistance. It is assumed that the weed seeds buried during the inversion process will lose viability during this period. However, long-term seedbank persistence following soil inversion has not been investigated. If the buried seeds retain viability, subsequent inversions or other deep-tillage operations may return them to the soil surface, potentially replenishing the weed seedbank. The current study identified 30 sites within the wheatbelt of Western Australia (in 2020) that had previously been subject to a single soil inversion event, to investigate viability of the buried seed. At each site, soil was sampled at 10-cm increments from 0 to 40 cm, and weed seedling emergence from these samples was assessed during the following year. Weed emergence was dominated by six species: rigid ryegrass ( Lolium rigidum Gaudin), subterranean clover ( Trifolium subterraneum L.), prostrate knotweed ( Polygonum aviculare L.), clammy goosefoot Dysphania pumilio (R. Br.) Mosyakin & Clemants, capeweed Arctotheca calendula (L.) Levyns, and ripgut brome ( Bromus diandrus Roth). Weed emergence was greatest from the 10- to 20-cm soil depth, with limited weed emergence beyond this depth, despite inversion operations generally placing topsoil below 20-cm depth. Of the six predominant species, the seedbank persisted for at least 8 yr, except for B. diandrus . This species did not emerge from sites where the inversion was performed more than 2 yr before the survey. This likely reflects species-specific differences in seed size and seedling emergence depth, as B. diandrus produces relatively large seeds capable of emerging from 10 to 20 cm (i.e., the most common burial depth). The findings confirm that the buried seedbank for most species remains viable over extended periods.