Why Do We Need Earthworms?

The activity of earthworms is most easily appreciated by comparison with the situation in regions where they are absent: the decomposition of organic matter there is slow, such that layers of litter accumulate on the soil surface and fail to be incorporated into the soil.

More specifically, the activity of earthworms is important  in four respects, in that they:

  • improve soil structure
  • mix and till the soil
  • aid in humus formation
  • increase the availability of plant nutrients

The burrowing of earthworms improves the physical structure of the soil, creating channels through which plant roots may more easily penetrate the soil. In addition to increasing soil porosity and aeration, this activity also improves soil drainage and water penetration while eliminating hardpan conditions. 

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Earthworms may also enhance soil structure through the formation of aggregates. Secretions in earthworm intestines cement soil particles together into aggregates which aid in erosion control. 

Man, through agricultural practices, such as cultivation, may temporarily improve soil structure, but the earthworm has longer-term effects in maintaining soil tilth.

As earthworms burrow through the earth, they consume large quantities of soil and fresh or partially decomposed organic matter from the soil surface, depositing it as fecal matter, or casts, in the lower soil horizons. Similarly, soil from the subsoil horizon is moved by these animals to the upper levels where it is mixed with the surface soil, resulting in a more uniform distribution of plant nutrients.

Charles Darwin (1881), the naturalist famous for his ideas on evolution, estimated that 10.6 tons of materials are brought to the soil surface of each acre by earthworms (or approximately St/hectare).

Through the ingestion of organic matter earthworms are important to the initial breakdown as well as to subsequent decomposition of organic matter. In fact, earthworms may consume more surface organic matter than all other soil animals together.

This material is eventually excreted as casts, concentrating nutrients and rendering them more water-soluble and available to plants.
Researchers have found that worm casts are generally richer in exchangeable calcium, potassium, and phosphorus than the surrounding soil, while earthworms themselves and their excretions are valuable sources of nitrogen. By bringing soil nutrients to the upper horizons from the lower subsoil, the earthworms counteract the effects of leaching whereby many nutrients are washed from the root zone and consequently rendered unavailable to plants.