Earthworms in Agriculture and Mining

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.

Earthworm Species


Earthworms are classified into three main categories:

  1. Epigeic species - leaf litter or compost-dwelling worms that are nonburrowing, live at the soil-litter interface and eat decomposing organic matter;

  2. 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;

  3. 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.

Earthworm Benefits


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:

Soil pH

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.


Organic Matter

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.


Soil Moist

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.


Drainage

Earthworms need soil to be aerated, so you may need to drain or mound soil in wetter areas to prevent waterlogging.


Soil Compaction

It is difficult for earthworms to move through heavily compacted soil, so keep equipment or animal traffic to a minimum in wet conditions.

Cultivation

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.


Climatic Extremes

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 the return of native flora. Because earthworms greatly influence soil structure and chemistry, their presence is likely to accelerate soil restoration and improve primary production. Sites using this method have observed advances in the return of ecosystem services that previously took much longer to re-establish.


Soils disturbed after mining are hostile to earthworms because of the lack of structure, the compaction during the stockpiling process, low organic matter content, unfavorable moisture conditions, and very low pH. Studies show that the survival rate of earthworms in the surface of the soil stockpiles can be high enough to act as a reservoir for re-colonization of re-spread soils. Earthworms surviving the stockpiling process can re-colonize rehabilitated soils within 10–30 years. Best results are obtained in conjunction with efficient plant restoration programs because plant roots enhance earthworm burrowing activity, and more importantly, decaying plant parts provide the necessary food resource.

Earthworm Breeding


1. Preparation

The main environmental factors affecting earthworm breeding and health are temperature, moisture, aeration, pH, and food material. There are certain care requirements that must be met for successful earthworm breeding:

  • Temperature. The ideal temperature for earthworm breeding is between 60°F and 80°F to facilitate intensive cocoon production and hatching. If the temperature is too low, earthworms may die; if the temperature is too high you can lower it by adding water or fans.

  • Moisture. The ideal moisture for earthworm breeding ranges from 60 to 85 percent to keep it crumbly moist, not soggy wet. Earthworms should be protected from the direct sunlight to prevent drying out and overheat.

  • Aeration. Earthworms can live at relatively low oxygen and high carbon dioxide environment, however, in the complete absence of oxygen they can die. Keep the moisture in check, as well as the amount of feed to maintain the right amount of oxygen for the earthworms.

  • pH. Earthworms will grow in a pH range between 5.0 (acid) and 8.0 (alkaline). Check pH regularly at different levels of the earthworm bed (top, middle, and bottom). If it’s too acid, agricultural lime (calcium carbonate) may be mixed with bedding material to remedy the condition.

2. Bedding

Earthworm beds may be constructed from many materials, including lumber, concrete or cinder blocks, brick, concrete, or hollow tile. Do not use cedar, redwood, or other aromatic lumber for the beds, as they contain tannic acid and resinous saps that are harmful to earthworms. Any convenient length is satisfactory, but the width should not exceed 30 to 40 inches, and the height should not exceed 18 inches to permit easy harvesting.

Typical bedding materials include stable compost (not high in soluble salts), horse manure that has aged for at least a few months, aged leaf mold, shredded brown leaves, shredded paper, or coconut coir. It should retain moisture, remain loose, and not contain much protein or organic nitrogen compounds that readily degrade to avoid pH increasing.


3. Feeding

Animal manures, garden compost, shredded or chopped cardboard, wood or papers or almost any decaying organic matter or organic waste product may be used as feed or to produce feed for earthworms. The protein content of the total feed should not be less than 9 percent and no more than 15 percent. With too little protein earthworms do not grow well; with too much protein, feed decays quickly and the beds become too hot for the worms. Earthworms should be fed usually once a week.


4. Harvesting

Earthworm beds should be harvested on a regular basis (usually every 30-45 days) to ensure maximum worm production and minimum disturbance of beds. It may be accomplished by several methods, though one harvesting method commonly used is known as "table harvesting": place a table or a board by the earthworm bed with a container of pre-soaked bedding for the harvested earthworms. Use a pitchfork to carefully lift off the top 3 or 4 inches of bedding and place it into the harvesting board. Make sure to have a bright light to make earthworms burrow down nearer the bottom of the bedding to escape the light. Then gently remove the top inch of the bedding pile and repeat the process until all earthworms are harvested.


5. Pests

Earthworms are subject to attack by a variety of pests. Most outbreaks are the result of poor bed management. Arthropods such as mites and ants are probably the greatest concern to earthworm growers.

  • Mites. Mites are natural inhabitants of manures and similar organic materials. All earthworm beds contain small populations of mites, which under certain conditions may reach extremely high levels. If worm beds are not cared for properly, acidity can build up and create conditions that allow mites to thrive. Routinely check pH and add agricultural lime if the pH is less than 6.8.

  • Ants. Several species of ants may occasionally be a problem or annoyance to worm growers. Ants are attracted to high-concentrate feed in earthworm beds, and some species are reported to feed on eggs and small worms. Ants can be controlled with baits and insecticidal sprays outside the beds but take precautions to prevent injury to the earthworms.


Conclusion


Earthworms may not be as attractive, but they are definitely very important due to their contribution to our world. These creatures play a vital part within the natural soil ecosystem as they 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.

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