Demonstrating spray-on mulch in vineyards
A 12 month project investigating the potential of a sprayable biodegradable mulch across a multitude of horticultural farming systems has recently been completed.
The CSIRO developed ‘Sprayable Biodegradable Polymer Membrane’ or more simply ‘spray-on mulch’ as a sustainable alternative to plastic mulch film. The spray-on mulch promised to have similar properties to plastic mulch in that it helps retain soil moisture and suppress weed growth while maintaining healthy soils and eliminating the need to manage the disposal of the plastic waste.
The product consists of a 20% by weight polyurethane emulsion in water, it is black in colour and has the consistency of thick paint. The majority of treatments made in this project were applied at a rate of 1 L/m2. Some trial and error was endured to develop the ideal application equipment and procedure for the small scale demonstrations. Consequently, the equipment used for application consisted of a 9 L watering can with a detachable spray head. Compared to a pressurised sprayer, the watering can suffered fewer blockages and was easier to clean while producing a smooth and even surface film.
DPIRD researchers established demonstration sites in wine grape vineyards (Margaret River and Frankland River), table grape vineyards (Swan Valley), a pumpkin and tomato farm (Carnarvon), and a carrot farm (Myalup). Multiple treatments were applied to each of the sites to compare the performance of the spray-on mulch to conventional practices and bare soil. Soil moisture, soil temperature and weed growth was observed over a period of time.
Specifically for the wine grape vineyard site, 3 undervine treatments were replicated 3 times. The treatments consisted of bare soil, remnant vegetation post herbicide application (conventional practice) and spray-on mulch on bare soil (with a line left untreated directly under the dripper to allow irrigation infiltration).
The soil at the Margaret River site was described as sandy loam while the Frankland River vineyard was gravelly loam.
Table 1: Soil moisture as expressed as average daily soil moisture loss (VWC%)
Region | Bare soil | Conventional practice | Spray-on mulch |
| Margaret River | 0.31 | 0.30 | 0.14 |
| Frankland River | 1.23 | 1.23 | 1.18 |
The spray-on mulch at the Margaret River vineyard appeared to have reduced daily soil moisture loss by around 50% when compared to the 2 other treatments. However, a similar impact was not observed in Frankland River with only a 5% reduction shown.
Table 2: Soil temperature expressed as average daily soil temperature variation (°C)
Region | Bare soil | Conventional practice | Spray-on mulch |
| Margaret River | 4.81 | 1.35 | 1.69 |
| Frankland River | 3.61 | 3.34 | 4.15 |
Another contrasting observation between the 2 sites was the soil temperature. The spray-on mulch in Margaret River reduced temperature variation similar to the conventional treatment but in Frankland River the spray-on mulch increased the daily soil temperature variation more than the other 2 treatments.
Table 3: Weed emergence expressed as extracted weed mass (kg/m2)
Region | Bare soil | Conventional practice | Spray on mulch |
| Margaret River | 0.24 | 0.24 | 0.27 |
| Frankland River | 0.31 | 0.30 | 0.20 |
There was only a small variation of weed emergence observed in Margaret River, but the spray on mulch in Frankland River showed around 40% reduction in weed growth.
Conclusion
- The spray-on mulch showed potential to reduce soil moisture loss.
- Ground preparation was crucial for success, having remnant vegetation or debris risked an incomplete mulch film forming.
- The formulation requires further enhancement so to reduce the volume/weight of the product i.e. develop into a powdered form to hydrate onsite and potentially examine reflective colours.
- Existing vineyard spray equipment are unlikely to be suitable for application due to blockage issues.
- Might not be ideal for annual undervine application but could be suitable in young establishing vineyards or nurseries.
- The spray-on mulch is yet to be commercialised and therefore costs of the product and application are unknown.
This project was funded by the Australian Government’s Agricultural Innovation Hubs Program, with support from the Department of Primary Industries and Regional Development (DPIRD) and was initiated through the South-West WA Drought Resilience Adoption and Innovation Hub.
CSIRO partnered in this project and the team thanks the numerous DPIRD staff who contributed to this project and the growers who hosted demonstration sites.
