Exploring the secret life of worms
Earthworms can dramatically alter soil structure, water movement, nutrient dynamics, and plant growth. Although these important indicators of soil health may not be immediately visible, particularly during the summer months, the piles of organic residues (middens) made by the earthworm species, Lumbricus terrestris - the largest in the UK, can still be seen.
As this deep-burrowing, but surface feeding species is nocturnal, it is often difficult to view their activity. Thanks to a recently-acquired infra-red camera, however, Dr Stroud is now able to monitor these worms foraging at night; between 10.00 pm and 2.00 am when it is warm and wet when this species of worms is particularly active.
Dr Stroud says: “These fascinating creatures are the underground engineers of our ecosystem whose multiple roles are too often poorly appreciated and threatened.
“I used to go out with a torch, but as they are extremely sensitive to light, they would go back into their burrows, so the camera has made a huge difference.”
One of the major threats to earthworm communities is that anecic (deep-burrowing) and epigeic (surface feeders) earthworms are harmed by tillage operations, she warns. However, endogeic worms (topsoil dwellers) can survive it and even sometimes benefit from it.
The soil scientist is undertaking field investigations to compare performance of wheat grown with and without the presence of Lumbricus terrestris, the most common deep-burrowing earthworm in the UK, to assess the effects of healthy and unhealthy populations of deep-burrowing earthworms. Her research started in conventionally managed agricultural soils, where she discovered that deep-burrowing earthworms and their associated middens were rare. Moreover, these were none of these earthworms - which were locally extinct - after growing root crops such as potatoes or onions, which involves high intensity soil cultivations, She then moved on to looking at different types of minimum tillage operations (min-till) where deep-burrowing earthworm populations were typically around 5/sq. m. However, this was far from the >30/ sq. m abundance of this species which is linked to benefitting plants.
This led her to a dramatic rethink of soil management. “The highest earthworm numbers are found under no-tillage, so I set up the first zero-tillage experiment at Rothamsted and re-introduced 30/sq. m deep-burrowing
Her work has also revealed that although field margins have high densities, they do not act as a source of earthworms for repopulating the field quickly. “This means the recovery of earthworm populations likely relies on the residual, surviving in-field worm populations,” she warns.
To make matters even more difficult, repopulation in deep burrowing earthworms is very slow, so Dr Stroud has also been assessing the potential of remedial actions such as the addition of compost or farmyard manure (FYM).
“We found applications of FYM under minimum tillage (min-till) resulted a 40 per cent increase in these earthworms over compost,” she says, adding that as yet she does not know whether this resource is equally efficient on every soil type. “Further research has shown that their middens are bigger and have higher biological activity and concentrations of the plant nutrients P, K and S when the soil has received FYM.
“Therefore, the middens themselves have novel functions that I hope to discover during my research.”