At Dawson Melon Co. in Red Cliffs, Victoria, a series of demonstration trials led by the Soil Wealth and Integrated Crop Protection (Soil Wealth ICP) project has provided valuable insights into alternative ground cover strategies for melon production. The primary aim has been to evaluate substitutes for single-use plastic mulch, a common but increasingly scrutinised product due to its environmental impact and disposal challenges.
Straw as a cover crop mulch alternative
In the 2023-24 season, a demonstration trial was established to test whether straw could serve as a functional substitute for a cover crop mulch. Straw was chosen over a traditional cover crop mulch as the window between rockmelon planting and potential cover crop growth was too narrow to allow sufficient biomass accumulation.
The trial compared multiple treatments, combining different mulch types – straw, bare soil, and plastic – with or without the application of metham sodium. Rockmelons were planted in late November following a glyphosate application, with soil temperature loggers installed at 10cm depth to monitor conditions throughout the season.
Initial results were encouraging from a soil temperature perspective. Data showed that straw mulch, particularly at the higher application rate of 10 t/ha, was effective at moderating soil temperature, keeping it consistently within the optimal 22-28°C range for melon seed germination and insulating it during the very hot summer days typical of the area. However, weed pressure soon became a major issue.
The straw imported for the trial contained a high load of weed seeds, including barley volunteers, which germinated rapidly and established aggressively. These weeds outcompeted the melon seedlings across the straw treatments, ultimately forcing the abandonment of weed control efforts and yield data collection.
Despite the setback, this trial provided valuable confirmation that organic mulches can offer agronomic benefits such as soil temperature stability. However, contamination risks, logistical challenges, and the cost of straw and installation materials (including netting to hold it in place) indicated that straw mulch, in its current form, was not scalable or commercially viable.
Trialling cereal rye mulch
Building on these findings, the second demonstration trial in the 2024–25 season focused on a more integrated approach: growing cereal rye as a dedicated cover crop and using its terminated biomass as mulch.
The rye was sown in June at a rate of 100 kg/ha over an area previously cropped to melons. It was terminated in September by rolling and chemical application, with narrow strips left standing to serve as in-field windbreaks. The goal was to create a mulch layer that would suppress weeds, reduce evaporation, and contribute to soil health.
Unfortunately, seasonal conditions posed major challenges. Rainfall between June and September was only about half the historical average, significantly limiting rye biomass production. The estimated dry matter yield was just 4 t/ha – insufficient for reliable weed suppression.
Then, in a reversal of fortunes, a four-day rain event in late November, immediately after melon planting, triggered a rapid and dense weed flush. The rye mulch, while still visible on the surface, was unable to act as an effective barrier. Weed seedlings established through the residue, particularly in the centre of the beds, where they competed directly with the melon crop for water and nutrients delivered via fertigation.
Given the high level of weed pressure and the limited efficacy under these conditions, no fruit was harvested from the trial area. In-crop mechanical control was ruled out due to the risk of disrupting the mulch layer, and selective herbicide use was considered too risky given the sensitivity of young melon plants and the weed species involved.
The trial reaffirmed that cover crop systems require proactive management and favourable conditions to succeed. Biomass quantity was a limiting factor in this instance, and it is clear that to be effective as a plastic mulch alternative, a cover crop must be established early, supported with irrigation, and possibly fertilised to ensure robust growth. Cereal rye, while promising in terms of decomposition rate and weed suppression potential, must reach sufficient biomass levels to provide those benefits. Moreover, any strategy involving organic mulch will likely need to be integrated with additional weed management tools, such as selective herbicides or timely manual control.
Grower Ash Dawson remains committed to finding alternatives to single-use plastics.
“We’re still committed to reducing single-use plastics, even with the challenges,” he said.
“It was encouraging to see that bare soil held up well in terms of fruit numbers, just slightly smaller fruit compared to the plastic-mulched beds.”
The smaller fruit size could be addressed through varietal selection, for example choosing cultivars with inherently larger fruit, partially mitigating the impact of removing plastic mulch.
What’s next?
Looking ahead, Ash Dawson plans to trial different cover crop species and combinations, including various cereals and possibly mixes with legumes.
There is also interest in incorporating biofumigant crops like mustard, cereals and resting the ground, to improve soil health and manage soil-borne diseases.
Although the trials did not yield the expected crop outcomes, they successfully highlighted the key crop management considerations, and potential pitfalls, involved in transitioning away from plastic mulch.
Mulches made with alternative materials such as paper and biodegradable plastics are being considered for the future demonstration trials.
Melons project lead Umberto Calvo believes it is worth persisting with cover crops.
“While the results weren’t what we hoped for this time, the trials gave us valuable insights into the complexities of moving away from plastic mulch,” he said.
Cover cropping remains a viable pathway, but one that requires careful planning, technical integration, and continued research to adapt to the realities of commercial melon production.
The Soil Wealth ICP project remains committed to supporting the melons industry with practical solutions for sustainable production systems – stay tuned for the full results of this case study.
Learn more
For more information, please contact project leader Umberto Calvo on 0448 189 847/ [email protected] from Applied Horticultural Research.
