Strategic tillage in Australian conservation agricultural systems to address soil constraints: How does it impact weed management?

Abstract

In the conservation agricultural systems practised in Australia, cultivation is not commonly utilised for the purpose of weed control. However, occasional use of tillage (strategic tillage) is implemented every few years for soil amelioration, to address constraints such as acidity, water repellence or soil compaction. Depending on the tillage method, the soil amelioration process buries or disturbs the topsoil. The act of amelioration also changes the soil physical and chemical properties and affects crop growth. While these strategic tillage practices are not usually applied for weed control, they are likely to have an impact on weed seedbank burial, which will in turn affect seed dormancy and seedbank depletion. Strategic tillage impacts on seed burial and soil characteristics will also affect weed emergence, plant survival, competitive ability of weeds against the crop and efficiency of soil applied pre‐emergent herbicides. If growers understand the impacts of soil amelioration on weed demography, they can more effectively plan management strategies to apply following the strategic tillage practice. Weed seed burial resulting from a full soil inversion is understood, but for many soil tillage implements, more data is needed on the extent of soil mixing, burial of topsoil and the weed seedbank, physical control of existing weeds and stimulation of emergence following the tillage event. Within the agronomic system, there is no research on optimal timing for a tillage event within the year. There are multiple studies to indicate that strategic tillage can reduce weed density, but in most studies, the weed density increases in subsequent years. This indicates that more research is required on the interaction of amelioration and weed ecology, and optimal weed management strategies following a strategic tillage event to maintain weeds at low densities. However, this review also highlights that, where the impacts of soil amelioration are understood, existing data on weed ecology can be applied to potentially determine impacts of amelioration on weed growth.

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

“…Seed size was likely not a factor in burial, even though B. diandrus seed is much larger than L. rigidum seed (Borger et al 2020), as seeds of both species were not found beyond 20 cm. There are no data in the literature on seed burial or subsequent emergence by soil loosening via deep ripping and little data on weed emergence following the use of subsoilers (Mia et al 2023). The current study highlighted that it was the only technique to place seeds beyond a depth of 20 cm reliably, resulting in a considerable proportion of seeds that are unlikely to emerge in subsequent years.…”

“…Seed size was likely not a factor in burial, even though B. diandrus seed is much larger than L. rigidum seed (Borger et al 2020), as seeds of both species were not found beyond 20 cm. There are no data in the literature on seed burial or subsequent emergence by soil loosening via deep ripping and little data on weed emergence following the use of subsoilers (Mia et al 2023).…”

“…In conservation agricultural systems in southern Australia, the crop is sown using narrow-point or disk openers in a single pass for minimal soil and residue disturbance. There is rarely cultivation for seedbed preparation or cultivation before or after crop emergence for direct interference with germinating or emerged weeds (Mia et al 2023). Crop seeding in this system results in very little mechanical weed control, partly because there is minimal soil disturbance at seeding and because "dry" sowing on the bare ground before the season-opening rains is common (Fletcher et al 2016).…”

“…Deep burial (10 cm) prevented the emergence of L. rigidum and reduced the emergence of B. diandrus . However, weed seed burial following strategic tillage has only been extensively researched for soil inversion (Mia et al 2023), with a full soil inversion shown to bury 50% to 99% of weed seed beyond a depth of 10 cm and to kill up to 99% of existing weeds (Mohler et al 2006; Roger-Estrade et al 2001). Soil mixing with rotary spaders has little research available on weed seed burial.…”

“…However, seed burial by soil mixing with large offset disks has been investigated, with the SeedChaser model by Spokas et al (2007) indicating that more than 95% of seed would be left in the top 0 to 10 cm. Subsoilers (similar to deep rippers) increase weed density in the following season or leave density unaffected compared with direct seeding (Davies et al 2019; Mia et al 2023; Yalcin and Cakir 2006). However, most studies were conducted in loam soils, and the researchers acknowledged that the response will likely vary in sandy soils (Spokas et al 2007; Yalcin and Cakir 2006).…”