An earthworm is a tube-shaped, segmented worm that is commonly found living in soil, feeding on live and dead organic matter. Earthworms are far less abundant in disturbed environments and are typically active only if water is present.
Earthworms are classified into three main categories:
Epigeic species - leaf litter or compost-dwelling worms that are nonburrowing, live at the soil-litter interface and eat decomposing organic matter;
Endogeic species - topsoil- or subsoil-dwelling worms that feed (on soil), burrow and cast within the soil, creating horizontal burrows in upper 10–30 cm of soil;
Anecic species - worms that construct permanent deep vertical burrows which they use to visit the surface to obtain plant material for food, such as leaves.
Earthworms have a big impact on the soil system healthiness. Usually, their presence indicates healthy soil. Earthworms offer many benefits:
Improve Nutrient Availability
Earthworms feed on plant debris (dead roots, leaves, grasses, manure) and soil. When the earthworm excretes this in the form of casts, plants get access to available minerals and nutrients in the soil. Studies in the United States show that fresh earthworm casts are five times richer in available nitrogen, seven times richer in available phosphates, and 11 times richer in available potassium than the soil.
Stimulate Microbial Activity
There are many microorganisms present in earthworm casts. As organic matter passes through their intestines, it is fragmented and inoculated with microorganisms. Increased microbial activity facilitates the cycling and conversion of nutrients from organic matter into forms readily taken up by plants.
Improve Soil Fertility
Earthworms improve soil fertility by turning organic matter into rich humus. They pull organic matter such as leaf or manure in the burrow, then shred, partially digest and mingle it with the earth. Earthworms casts can contain 40 percent more humus than the top 9" (23 cm) of soil in which the earthworm is living.
Improve Soil Structure
The earthworm's burrowing creates passages for air and water to travel through the soil which maintains the soil structure, enabling processes of aeration and drainage. They also modify the vital organic component that makes a soil healthy. Deep-burrowing earthworms make channels in the soil which makes it easier for roots to penetrate deep into the soil and take necessary nutrients. Earthworms can also rebuild topsoil by leaving their casts on the soil surface. In favorable conditions, they can bring up about 50 t/ha annually, enough to form a layer 5 mm deep.
Improve Drainage and Water-Holding Capacity
Besides fragmenting organic matter, earthworms loosen and aerate the soil which helps to improve water-holding capacity. They also enhance porosity and drainage by channeling, burrowing and moving through the soil. Some species make permanent burrows deep into the soil for drainage, particularly under heavy rainfall. At the same time, the burrows minimize surface water erosion. Overall, soils with earthworms drain 10 times faster than soils without earthworms.
Earthworm Habitat Conditions
Earthworm populations depend on both the physical and chemical properties of the soil:
Earthworms don’t like acid soils with a pH less than 4.5. Besides, earthworms need a continuous supply of calcium, so the addition of lime that raises pH and adds calcium would be a good solution for maintaining soil pH for earthworms.
Since earthworms feed on soil and dead or decaying plant remains you must maintain the constant provision of food for earthworms. The addition of organic matter, preferably as a surface mulch, on a regular basis, will provide earthworms with their food. Crop rotation also helps build up organic matter levels and earthworm numbers.
Use of Fertilizers and Fungicides
Highly acidifying and nitrogenous fertilizers such as ammonium sulfate and some fungicides reduce worm numbers. Make sure to pick the right chemicals if you want to keep earthworms in the soil.
Earthworms need moisture to stay alive as they lose about 20% of their body weight each day due to castings. Decaying organic matter (humus) holds moisture in the soil. In dry times some species burrow deep into the soil and stay inactive until rain 'reactivates' them.
Earthworms need soil to be aerated, so you may need to drain or mound soil in wetter areas to prevent waterlogging.
It is difficult for earthworms to move through heavily compacted soil, so keep equipment or animal traffic to a minimum in wet conditions.
Plowing reduces earthworm numbers. Studies show that after four years, no-till land had twice as many earthworms as cultivated soils. However, shallow cultivation may not affect worm numbers.
Earthworms don’t tolerate drought and frost, as well as dry sandy soils. They are active only when the soil is moist. Organic matter cover helps reduce the effect of climatic extremes and retains soil moisture.
Earthworms and Mining
The ability to break down organic materials and excrete concentrated nutrients makes the earthworm an important player in mine-site restoration projects. In response to ecosystem disturbances, some mining sites utilize earthworms to prepare the soil for t