What was it all about?

Earthworms are known to be an indicator of healthy soil function. However, there has been limited research into how commercial vegetable farming practices impact on earthworm activity levels and how earthworms can potentially contribute to farm productivity.

Conducted from 2016 to 2019, this project aimed to investigate and promote the benefits of increased earthworm activity for commercial vegetable farms. The research included:

• A literature review of the potential benefits of earthworm activity in commercial vegetable growing, and the factors that affect earthworm populations and activity
• Detailed field research carried out at two sites in Victoria and Tasmania, with a further 16 demonstration sites across Australia
• An economic assessment of the possible productivity benefits of farm practice changes that increase earthworm activity.

Earthworms can have beneficial effects on surface and sub-soil structure and fertility. However, many common practices in commercial vegetable growing have negative impacts on earthworm populations and activity.

Practices that improve soil health – such as increasing soil organic carbon levels, reducing tillage intensity and depth, and more sensitive farm chemical use – can increase earthworm numbers and activity and have significant soil structure and fertility benefits.

The most significant factors influencing earthworm activity were found to be:

• Using green manures and crop rotations to build levels of labile carbon. The farms that had green manures or pasture phases in their crop rotations had high earthworm numbers, with the effect of burrows and casts on sub-soil structure apparent.
• Reduced intensity and depth of tillage. On most of the studied soils, rotary hoe tillage deeper than 300mm greatly reduced earthworm numbers. This was more marked at sites where tillage depth was to clay pans or gravel layers. Two sites with intensive tillage were found to have healthy earthworm numbers, however both these sites had sub-soils deeper than the tillage depth, allowing some earthworms to survive and recolonise areas.
• Soil moisture. Soils that had experienced significant and prolonged drying down the soil profile had low earthworm numbers, despite good soil management practices.
• Sensitive chemical use. Sites using integrated soil management and biological agents for disease control and soil health enhancement had higher earthworm numbers. However, some sites with scheduled regular use of insecticides and fungicides, but with high levels of labile soil carbon and reduced intensity tillage, had healthy earthworm numbers.

Cost/benefit analysis revealed that soil management practices that promote earthworm activity led to reduced input costs and increased yields.

The main economic value of earthworm activity included:

• Reduced soil compaction and reduced need for tillage
• Reduced need for fertilisers due to ‘manuring’ with earthworm casts
• Deeper and healthier plant root growth
• Increased yields per unit of input.

To date, little work investigated the impacts of earthworm activity on vegetable crops, but yield increases of more than 10 per cent have been reported on pasture and cropping systems. Trials of soil management practices that improve organic matter levels and soil structure in vegetable farms have reported yield increases of 5-10 per cent. This cannot all be attributed to earthworm activity, although they can make a significant contribution to soil structure and fertility.

ACT NOW

Read more about how to utilise earthworms in commercial vegetable growing with these fact sheets developed by the project team:

• Fact Sheet 1: Earthworms and your farm provides guidance about how to get the most benefit from earthworms in commercial growing systems.
• Fact Sheet 2: Are earthworms working for you? explains how to check whether you have a healthy population of earthworms and the types you are likely to find.
• Fact Sheet 3: Working with earthworms shares how growers can achieve the best results.

You can also download the project’s fact sheet Working with worms – improving productivity using vermiculture in commercial vegetable growing.