BY DIMI KYRIAKOU, RMCG

Cover crops, nutrient use efficiency and crop health were the key topics of discussion at the Soil Wealth ICP demonstration site farm walk in Skye, Victoria on Wednesday 7 May.

The event attracted around 20 industry members including local vegetable growers, agronomists and industry to the demonstration site at Butler Market Gardens, which produces spring onions, herbs and a range of Asian vegetables about 50 kilometres south-east of Melbourne.

The site is dominated by sandy loam soils which – as a result of the intensive cropping regime typical for market gardens – are generally lacking in organic matter and overall soil health and structure.

The Soil Wealth ICP team has been working with Butler Market Gardens owner Rick Butler and operations manager Dale Creed to trial ways to effectively manage nutrients at the site and improve soil nitrogen cycling and organic matter retention. This has included the use of nitrogen-fixing cover crops such as legumes, with a view to ultimately reduce the use of synthetic fertilisers on the farm.

The trial is using plant and soil testing as well as in-field monitoring to understand nutrient uptake and balance and reduce nitrogen losses.

Attendees heard insights from Rick and Dale as well as Soil Wealth ICP team members Camilla Humphries and Doris Blaesing, and Bruce Scott from Campbells Fertilisers.

Key takeaways

Dale and Camilla explained the site trialled three cover crops including a mixed legume species (lablab, cowpea, soybean and sun hemp), buckwheat/vetch and sorghum, with the latter producing the highest above ground biomass and nitrogen uptake for recycling to the soil. The level of labile carbon – a food source for microorganisms and a key indicator of soil health – was demonstrated with a quick in-field test which showed a significant improvement in the trial area which housed the sorghum cover crop and is now growing a cash crop.

Doris explained that cover crops have been a key focus for the Soil Wealth ICP project since its inception and has been informed by many lessons learnt along the way, particularly through demonstration sites.

Cover crops can also outcompete weeds and can help improve soil organic matter and soil structure, protecting the cropping beds from erosion.

“If you’re looking to start with a cover crop, keep it simple, see what works in your system and learn from your mistakes. The benefits of cover crops are huge, and in an intensive rotation like a market garden, the benefits pay for themselves,” Doris said.

As soil-borne diseases such as Pythium, Rhizoctonia and Fusarium are common in market gardens, biofumigant cover crops such as mustards can be planted instead of using chemical fumigation. When the seeds are macerated, they release isothiocyanate compounds which produce a biocidal effect, similar to that of metham sodium which is toxic to fungal and bacterial pathogens.

Cover crops can also outcompete weeds and can help improve soil organic matter and soil structure, protecting the cropping beds from erosion. Cover crops are a good alternative to leaving paddocks in fallow as they help to improve soil biological processes by increasing the amount of labile carbon, providing an energy source for microorganisms to cycle plant available nutrients.

Dale added that Butler Market Gardens invested in a ‘spider seeder’ to help identify the main causes for poor crop germination in wet weather, and if it is due to the presence of pathogens in the soil or the planting equipment.

Finally, Bruce provided an overview of the role of different nutrients in vegetable production, particularly nitrogen, potassium and calcium. He highlighted the importance of understanding the soils you are working with and the context of open field versus protected cropping, as well as the application and type of fertilisers available.

Bruce reiterated the importance of knowing your base level of nutrients for effective monitoring through soil and plant testing and focusing on increasing organic matter in the plant rootzone to improve nutrient uptake.

Finally, Bruce explained how controlled release fertilisers can help make plant essential nutrients available throughout the crop cycle and that polymer-coated fertilisers can be used to protect nutrients from being lost either through leaching below the rootzone or volatilised as nitrous oxide into the atmosphere. The non-plastic polymer coating technology turns into a gel once wetted, allowing for the slow release of nutrients and is biodegradable.

What resonated with participants?

Attendees shared the following topics of interest from the farm walk as well as areas they will investigate further:

• Investigating labile carbon testing and soil-borne disease testing
• Increasing organic matter in soils
• Looking at cover crop options and ‘having a go’
• Understanding how cover crops assist vegetable production
• Advisors sharing knowledge with grower clients.

FIND OUT MORE
The Soil Wealth and Integrated Crop Protection (Soil Wealth ICP) project provides research and development (R&D) extension and communication services on improved soil management and plant health to the Australian vegetable and melon industries.

You can find out more about the trial results at the Skye demonstration site, and the many other aspects of the Soil Wealth ICP project, at soilwealth.com.au

You can also hear more from Dale Creed and Camilla Humphries about the trial and the field walk in these video and podcast episodes.