Author: Joanna Uglow.
Earthworms play an essential role in soil health and productivity, but many agricultural soils have become degraded and have very small populations. Earthworms provide benefits in the following ways:
- Better and more stable soil structure
- Create burrows which aerate the soil and allow water to infiltrate
- Worm casts are crumb-like and contribute to good soil structural units
- Nutrients are more available
- Organic matter is broken down by worms, making it more available for bacteria and fungi who release nutrients in plant available form
- Soil fertility is improved at depth as worms mix the soil
- Biodiversity
- Vital food source for birds such as song thrushes, robins and blackbirds
- Earthworms support bacteria and fungi through the breakdown of organic matter
Types of Earthworms
We have 29 species of earthworms in the UK alone and roughly 3,000 species globally. It can be difficult to identify earthworms to a species level especially without a microscope and, in some cases, it is not possible on living specimens. However, earthworms can be put quite easily into one of three groups based on their roles and location within the soil profile. These are:
How to encourage earthworms in agricultural soils
There are several practices that can be adopted to encourage earthworms.
- Increase soil organic matter: provide food sources as well as reduce extremes in soil temperature and moisture. Most appropriate methods include leaving crop stubble long / chopping straw, including grass in arable rotations, and applying compost.
- Reduce cultivations: ploughing has been shown to reduce earthworm numbers, while minimum tillage or direct drilling have less impact on their habitat.
- Avoid compaction: worms find it difficult to burrow through hard, compacted soil. Where possible, reduce trafficking or confine to designated areas and avoid high stocking densities to avoid causing compaction. Increased soil organic matter will also improve the soil’s resilience to compaction.
How to monitor earthworms
Earthworm counts
Spring and autumn are the best times to count earthworms. They are most likely to be found when soil is warm and moist.
- Dig a hole 20x20cm to about 30cm deep
- Sort through the soil counting worms as you go
- Repeat in at least 3 locations across the field
Per hole: <10 is poor, 10-20 is moderate, 20+ is good
Sources of further information
Contact FWAG SW if you would like a visit from an adviser to assist with soil assessments, earthworm counts and advise around soil management.
AHDB have a useful field guide to counting and identifying earthworms which can be downloaded and printed.
Field Studies Council have a more in-depth key for identifying earthworms which can be purchased from their website.