Charles Darwin spent the last years of his life studying earthworms, because he valued the importance of earthworms in the soil. He said, “It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures.”
We sometimes call earthworms ‘ecosystem engineers’ because they significantly modify the physical, chemical and biological properties of the soil profile. These modifications can influence the habitat and activities of other organisms within the soil ecosystem.
Why are earthworms soimportant for the soil?
They are essential recyclers of organic material. Earthworms, along with bacteria and fungi, decompose organic material. So they are important in the process of making compost. However, earthworms do the same in pasture soils. Here they decompose dung and plant litter and process literally tons of organic matter per hectare each year. They also recycle leaf litter under trees and shrubs.
Although earthworms derive their nutrition from microorganisms, many more microorganisms are present in their faeces or casts than in the organic matter that they consume. As organic matter passes through their intestines, it is fragmented and inoculated with microorganisms. Increased microbial activity facilitates the cycling of nutrients from organic matter. Nutrients like phosphorus and nitrogen become more readily available to plants after digestion by earthworms and being excreted in earthworm casts.
Earthworms can move large amounts of soil from the lower strata to the surface and also carry organic matter down into deeper soil layers. Their burrows also alter the physical structure of the soil. They open up small spaces, known as pores, within the soil.
When we introduce earthworms to soils devoid of them, their burrowing can lead to increases in water infiltration rates of up to 10 times the original amount. This brings water and soluble nutrients down to plant roots. Burrowing also improves soil aeration. This is important for both plants and other organisms living in the soil. It also enhances plant root penetration. At the same time, the burrows minimize surface water erosion.
Plant and crop residue are gradually buried by cast material deposited on the surface and as earthworms pull surface residue into their burrows.
Earthworms, like all creatures, are part of food webs. Their main predators are a wide range of birds and mammals that prey upon them at the soil surface.
How can we create soil conditions that encourage earthworms?
Because earthworms do not like soil that is too acid, alkaline, dry, wet, hot or cold, their presence is a good indicator of soil conditions suitable for plant growth.
If your soil is acid, add lime which will raise the pH and also adds calcium, which they need.
We know that earthworms feed on dead or decaying plant remains. This includes straw, leaf litter and dead roots, so spreading this kind of material on the soil as mulch will be useful. Turning green manure crops into the soil will have a similar effect. So will allowing crop stubble to decompose in the field.
Rotating pasture with crops helps build up organic matter levels and earthworm numbers.
Avoid the use of highly acidifying fertilisers such as ammonium sulfate and some fungicides, as they reduce worm numbers.
Keep the soil moist, because worms can lose 20% of their body weight each day in mucus and castings.
It is difficult for earthworms to move through heavily compacted soil, so keep vehicle and animal traffic in your pastures to a minimum, especially in wet conditions.
Using no-till methods of agriculture will result in an increase of worms in your soil.
You might find that some parts of your smallholding are richer in earthworms than others. What you can do is cut pasture sods from areas with high worm populations and transfer them to worm-free areas. New colonies will establish within a couple of years as long as there is plenty of organic matter, and soil and climatic conditions are favourable. It is important that you transplant pasture, not just worms.
Do not try and transplant compost worms into agricultural soils. Species that thrive in compost will not survive the harsher conditions of paddock soils, which dry near the surface.
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