A worm is just a worm……but not really. Earthworms come in many shapes, colours, and sizes. Different species are prevalent in different climates and they all have a role to play in the world around us. There are over a thousand different individual species of earthworms all over the world. There are different types of earthworms found in soil, and each one serves a unique purpose. In this article, we are going to delve into the three different types of earthworms and the role each of them plays in the soil below us.
Table of Contents
The three types of earthworms
Earthworms are classified into 3 ecological groups according to their localization in the soil, feeding behaviour, and burrowing.
1. Epigeic (1 to 2.5 mm in diameter, live and feed above the soil surface, forest litter, rarely burrow and ingest, and have very little effect on soil structure),
2. Anecic (4 to 8 mm in diameter, feed at the ground surface and decaying organic residues, live in semi-permanent burrows, more or less vertical and opened to the soil surface.
3. Endogeic (2 to 4.5m in diameter, Mostly live on 10 -15 cm surface, ingest soil, dig extensive system of burros to search foods and they immediately refill with their casts, the burrows are mostly subhorizontal oriented.
Earthworms used in vermicomposting
All the earthworms used in vermicomposting are in the epigenic category. They are very good at breaking down organic matter but aren’t particularly good at aerating soil. Common types used in vermicomposting include:
– Red wigglers: These earthworms are native to the United States and are used all over the world for vermicomposting. They thrive in a warm, moist environment and can eat their own weight in food every day.
– European nightcrawlers: Another commonly used earthworm, these guys can handle colder climates and are great for breaking down tougher materials like wood.
– African nightcrawlers: These earthworms can handle warmer temperatures than most other composting worms and are excellent at breaking down food scraps.
Earthworm Burrows
Burrows increase water infiltration, water storage and aeration; increase water movement to deeper soil horizons; modify root penetration. Earthworms vertically and horizontally burrow soil during feeding and moving. Burrow size and continuity depend on the soil properties as well as on earthworm species. The anecic species such as L. terrestris. Tends to build large vertical burrows in the soil when compared to most endogenic species.
According to this article earthworms with larger burrowing activity may also enhance soil drying. Anecic and endogenic earthworm species may enhance the soil drying process, relative to epigeic earthworm species.
Tilling and Earthworms
Soil properties as well as management practices also affect earthworm abundance and burrowing. Tillage disrupts the soil food web and has a disruptive effect on soil biology. Earthworm populations in no-till systems are significantly greater than in conventionally tilled systems. Tillage intensity, depth and soil types are important factors affecting earthworm abundance in soil.
How worm castings affect soil structure
Worm castings are enriched with organic matter and cations. In most cases, the bulk density of the casting is higher than that of the surrounding soil. Microaggregates are formed while passing through the earthworm’s gut, organic and inorganic materials are egested as worm castings.
As water is lost from the castings it strengthens the bonds among organic and inorganic particles. As a result, earthworm cast formation can increase soil aggregation, structure, and aggregated tensile strength. In general, cast stability is higher than the surrounding soil.
Castings of different species
The shape, size and composition of casts depend on earthworm species. In general, small species produce smaller casts, with a finer structure than the larger species.
Earthworms and water retention
Additionally, water runoff simulation clearly showed an enhancement of water infiltration with earthworm casting activity. The average water infiltration rate was about two times higher in the plots with earthworms. The presence of earthworms increased water storage in the soil by about 20% on average. This increase is mainly due to the formation of macroaggregates, which causes an increase in pore size and total porosity.
Earthworm types and soil structure
The different types of earthworms found in soil can have different effects on the soil. For example, earthworms that burrow deep into the soil can help increase water infiltration and retention. Additionally, earthworm castings can help increase soil aggregation and stability. Soil properties, as well as management practices, also affect soil’s water holding capacity.
Final Thoughts
Earthworms are important biological factors in soil ecosystems. They have positive effects on soil structure by reducing compacted soil’s bulk density, increasing tensile strength and aggregate stability, and opening macropores in soil The latter improves water-holding properties of soil. Improvements in soil are dependent on the soil type, cropping systems, and earthworm species.
Earthworm activity and castings could contribute to the stabilization of organic carbon in stable soil aggregates. The size of earthworms is also important for larger and stable soil aggregate formation. In general, large earthworms are responsible for the formation of the macroaggregate, while smaller earthworms can consume large aggregates and excrete small aggregates.
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