A new Soil Wealth ICP demonstration site at the Department of Primary Industries’ Ayr Research Facility in north Queensland is exploring how cover crops and biostimulants can work together to enhance soil health, resilience and productivity in melon production systems.
Fallow periods between crops can lead to declines in soil health. This trial is investigating whether integrating cover crops, alone or in combination with biostimulants, can help to restore soil function while improving crop yield and quality.
Running to the end of 2026, the study will test various combinations of cover crops and a Bacillus-based biostimulant to identify practical approaches that:
- Build soil structure and fertility
- Reduce erosion and weed pressure
- Promote more productive, resilient melon crops.
Trial design
The demonstration compares four cover crop options – sorghum, sunn hemp, Japanese millet with lablab, and mung bean – each grown with and without the biostimulant.
A bare fallow serves as the control. This side-by-side layout will reveal both the individual and combined effects of the treatments on soil health, crop performance and input efficiency.
Each treatment is replicated four times. Legume crops are inoculated before planting (Type I for mung bean and sunn hemp; Type J for lablab), with initial irrigation supplied via drip tape and rainfall.
Biostimulant treatments will be applied to the cover crops at germination and again at watermelon planting. The cover crops will be terminated by spraying before seed set, with residues left on the surface and then incorporated into the soil. A watermelon crop will subsequently be planted across the trial area in line with standard grower practice.
To track how the soil responds over time, baseline soil chemistry, biology and structure tests are taken before planting the cover crops and repeated at key stages throughout the trial.
Monitoring focus
The comprehensive monitoring program includes:
- Soil chemistry and nutrient status
- Soil biology
- Physical soil assessments – infiltration, compaction (penetrometer and bulk density) and aggregation
- Cover crop performance – biomass, weed suppression and carbon-to-nitrogen ratios
- Weed pressure observations
- Watermelon crop performance.
From soil quality to fruit quality
During the melon phase, the team will measure plant growth, soil condition and how the previous treatments influence crop performance.
Yield and quality data, including fruit size will be collected at harvest, alongside postharvest soil sampling to assess changes in nutrient levels, microbial activity and structure.
An economic analysis will run in parallel with the agronomic assessments, tracking input costs (seed, fertiliser, biostimulant, labour and water) against outcomes such as yield gains, improved soil health and reduced weed management costs.
The project is managed by Sophia Thach and Umberto Calvo from the Soil Wealth ICP team, with support from Reg Andison and the Ayr Research Facility team and agronomic input from Eilis Walker at Nutrien Ayr.
This project has been funded by Hort Innovation using the vegetable and melon research and development levies and contributions from the Australian Government.
