Bold claim: a smarter mulch solution could slash water loss in farming, reshaping how we protect soil moisture. New CSIRO research is exploring how crop residues can be engineered into composite mulch batts that break down over time to boost soil health while conserving more water. This work, supported by a three-year GRDC project, focuses on a sprayable mulch film tailored for broadacre cropping, especially in low-to-medium rainfall regions. Leading the charge is Dr. Stuart Gordon, a Senior Principal Research Scientist in CSIRO Agriculture and Food’s Systems Program.
The goal is clear: create a biodegradable water vapor barrier that is at least half as effective at reducing evaporation as traditional plastic sheets. It’s important to note that while laboratory tests show plastic sheets can be nearly 100% effective, real-world field conditions—tears, holes, rough edges, wind, and heat—reduce performance to roughly 35% moisture savings compared with no mulch. Plastic isn’t practical for large-scale farming, but straw mulch can offer a similar seasonal moisture benefit.
Encouraging progress is seen in controlled lab experiments: when soil pots with adequate watering are placed in a hot environment, the new mulch treatment can cut evaporation by as much as 40% (see Figure 1: Evaporation comparison). In essence, the researchers are targeting a performance indicator that balances practicality with effectiveness in real-world farming.
Powdered binder boosts mulch versatility
CSIRO began this line of work with patents for a sprayable, biodegradable mulch derived from a polyurethane-based aqueous emulsion that could be sprayed onto soil to suppress weeds and conserve moisture. Transporting a mostly water-based product proved expensive, so the team redesigned it into a friable powder: polyurethane particles coated with cellulose. These particles act as a binder to hold chopped windrowed straw or chaff together, forming a composite batt on the soil surface that lowers evaporation and reduces erosion.
With this batt on the soil, a microclimate favorable for seed germination emerges. If hotter or drier conditions demand a tighter seal, the batt can be compressed to enhance its barrier properties. The mulch powder is described as “tunable”: it can be applied dry or after dew or rainfall to activate or tackify bonds, mixed with water for spraying onto residues, or even melted with low-temperature rollers around 60°C to activate it.
The polyurethane backbone includes amine and urea groups that can feed soil microbes as the batt degrades. The material also affords some flexibility to prevent cracking or fall-apart behavior when the surface is disturbed, while the surrounding cellulose provides additional bonding sites.
Dr. Gordon emphasizes that the powder is ideally applied before seeding to create a composite batt over hard-setting or crusting soils, moderating drying and high soil temperatures. When combined with crop residues and moisture, the binder helps hold the residue together long enough for the crop canopy to form. The organic matter remains in place, and the binder helps secure it to the ground around the germinating seed, preserving moisture from recent rain or fallow periods and improving water infiltration.
Field trials are slated for 2026 in Horsham, Victoria, and Merredin, Western Australia, to evaluate performance and determine how sowing equipment may need adjustments to cut through the mulch layer and return soil and mulch over the emerging seed.
Broad potential with ongoing testing
Laboratory and small-plot trials in 2024–2025 confirm that the powdered formula effectively creates batts, preserves soil moisture, and aids mulch decomposition. Early results show over half of the binder’s mass biodegrades within about eight months, with continued biodegradation studies planned for soils with limited microbial activity at the Waite campus in South Australia.
There’s also room to adapt the product for weed suppression by adding pigment to block sunlight or to incorporate actives that protect against soil pathogens or nematodes. Since polyurethane can serve as a carrier, it could deliver slow-release active ingredients as it biodegrades.
Researchers are also exploring incorporating refined cereal residues into the binder system, including contributions from recycled cotton clothing. The University of Queensland team is investigating how crop-residue cellulose can be refined to act as an active component in the binder and composite batt endpoint.
Domestic production considerations and cost
Polyurethane is currently manufactured in Australia, mainly for the construction sector. A key question is whether the specific mulch-powder formula can be produced domestically at scale. Studies are underway to assess production costs and optimal application rates to ensure affordability and effectiveness. A prototype product is planned for release in 2026 to support further testing.
For more information, contact Dr. Stuart Gordon at CSIRO: stuart.gordon@csiro.au
