**2.9 Effects on physical properties of soil**

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


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 Bohlen, 1996; Lachnicht and Hendrix; 2001).
