**2. Ecological strategies of earthworms**

Lee (1985), recognised three main ecological groups of earthworms, based on the soil horizons in which the earthworms were commonly found *i.e.,* litter, topsoil and sub soil.

Earthworms and Vermiculture Biotechnology 89

between earthworm number and biomass and the organic matter content of the soil (Doube

Soil texture influences earthworm populations due to its effect on other properties, such as soil moisture relationships, nutrient status and cation exchange capacity, all of which have

Earthworms, which improve soil productivity and fertility (Edwards *et al.,* 1995), have a critical influence on soil structure. Earthworms bring about physical, chemical and biological changes in the soil through their activities and thus are recognised as soil

1. Ingestion of soil, partial breakdown of organic matter, intimate mixing of these fractions

During these processes, earthworms contribute to the formation of soil aggregates, improvement in soil aeration and porosity (Edwards and Bohlen, 1996). Earthworms contribute to soil aggregation mainly through the production of casts, although earthworm burrows can also contribute to aggregate stability since they are often lined with oriented clays and humic materials (Lachnicht and Hendrix; 2001). Most workers have agreed that earthworm casts contains more water-stable aggregates than the surrounding soil and by their activity influence both the drainage of water from soil and the moisture holding capacity of soil, both of which are important factors for plant productivity (Edwards and

Earthworms bring about mineralisation of organic matter and thereby release the nutrients in available forms that can be taken up by the plants (Edwards and Bohlen, 1996). Organic matter that passes through the earthworm gut is egested in their casts, which is broken down into much finer particles, so that a greater surface area of the organic matter is exposed to microbial decomposition (Martin, 1991). Earthworms have major influences on the nutrient cycling process in many ecosystems (Edwards and Bohlen, 1996). These are

Earthworms contribute nutrients in the form of nitrogenous wastes (Ismail, 2005). Their casts have higher base-exchangeable bases, phosphorus, exchangeable potassium and

important influences on earthworm populations (Lavelle, 1992).

Soil structure is greatly influenced by two major activities of earthworms:

and ejection of this material as surface or subsurface casts. 2. Burrowing through the soil and bringing subsoil to the surface.

**2.8 Effect of earthworms on soil quality** 

**2.9 Effects on physical properties of soil** 

Bohlen, 1996; Lachnicht and Hendrix; 2001).

**2.10 Effect on chemical properties of soil** 

usually based on four scales (Lavelle and Martin, 1992):

4. during the long-term genesis of the whole soil profile.

1. during transit through the earthworm gut, 2. in freshly deposited earthworm casts,

3. in aging casts, and

*et al.,* 1997; Ismail, 2005).

managers (Ismail, 2005).

**2.7 Soil texture** 

Bouché (1971, 1977), also recognised three major groups based on ecological strategies: the epigeics (Épigés), anecics (Anéciques) and endogeics (Éndogés). Epigeic earthworms live on the soil surface and are litter feeders. Anecic earthworms are topsoil species, which predominantly form vertical burrows in the soil, feeding on the leaf litter mixed with the soil. Endogeic earthworms preferably make horizontal burrows and consume more soil than epigeic or anecic species, deriving their nourishment from humus.
