Investigating Stubble Strategies - Is Burning the Answer?
By Melanie Dixon, WMG Mixed Farming Systems Officer & Kate Parker, WMG Graduate Project Officer
The time between harvest and seeding is when sandy soils are most at risk from wind erosion and topsoil nutrient loss. As the effects of increased climate variability become more pronounced, growers are looking at stubble retention as a valuable tool in helping protect soils over the summer months. Crop residues left after harvest offer nutrients, carbon, and a protective ground cover that lowers the risk of wind erosion. However, when residue is high after above average seasons, increased stubbles can mean seeder blockages during an extremely busy period of the farming calendar. The Western Australian Government State NRM funded Stubble Management Project is investigating alternatives to burning stubble and looking to the benefits that leftover crop residue can provide.
Stubble contains significant nutrients, and the ideal situation is being able to return these nutrients back into the soil, reducing potential mineral fertiliser input in the subsequent season. Groundcover also assists in minimising wind erosion and protecting the nutrient rich topsoil, with a general rule of thumb being to maintain levels of groundcover at 50% or above. Burning not only eliminates all protective groundcover but also removes potential nutrient gain. Approximately 80 per cent of nitrogen, 50 to 80 per cent of sulphur and 40 per cent of phosphorus can be lost to the atmosphere from burnt cereal stubble, with additional phosphorus and potassium being lost in ash.
As part of the Stubble Management Project, six demonstration sites were established in 2023 across the Northern and Central Wheatbelt to investigate how standing stubble, incorporation and an application of biostimulant (nitrogen) would compare. The timing of site establishment was ideal as stubble load was high in 2023 after two consecutive above average crop years. While there was no significant difference found in weed establishment, plant growth or harvest yield across all treatments, regardless of site location, there was also no observed downside to retaining the stubble on each of the sites. There was a slight negative impact on groundcover in machinery incorporation treatments, but this was not shown post-harvest and does not appear to be a long-term effect.
As stubble amounts vary from year to year, it is beneficial to have a range of options available without needing to weigh up the potential consequences to yield. Growers can tailor their management strategy to suit their current system, crop rotation and available machinery. Crop residue can be preserved, either as left standing or through machinery incorporation if the amount of stubble would impact the efficiency of seeding. With increased stubble management options, growers can review their strategies season to season. One possible opportunity provided by the retention of stubble rather than burning, is a long–term focus on increasing productivity through improved soil health and groundcover.
The West Midlands Group will continue to monitor the six demonstration sites involved in the project throughout 2024. There will also be a series of events showcasing the demonstration sites, and for growers to discuss all things stubble management and crop nutrition. The first (free) event will be held on Tuesday, 9th April at the Dandaragan Community Recreation Club (DCRC), with more details available on the event page. Read the full 2023 Stubble Management Project Seasonal Update here, and to follow along with the project and for helpful stubble management resources, head to the project page.
