Agriculture Reference
In-Depth Information
Mixing of surface-litter with the mineral soil, and its incubation in casts
The intimate admixture of organic and mineral components in the casts of anecic
earthworms results in the formation of stable organo-mineral structures. As a result, soil
organic matter in casts tends to be more highly humified than the originally ingested
plant material (Rafidison, 1982). The importance of this process in soil formation has
been emphasised elsewhere (see Chapter II). Microbial incubation in casts during
the few hours to days following their deposition may result in a significant release of
assimilable P (
e.g.,
Sharpley and Syers, 1977; Satchell
et al.,
1984), nitrogen fixation
(Shaw and Pawluk, 1986; M'ba, 1987) or denitrification (Elliott
et al.,
1990), depending
on micro-environmental conditions.
4.2.6.2
Soil physical properties
Porosity
Both anecic and endogeic earthworms contribute generally to the maintenance of elevated
soil porosity through the creation of galleries. Deposition of casts at the soil surface
regulates soil porosity since the volume of voids created in the soil is at least equivalent
to that of the casts and this may represent the annual formation of volumes of tens
of cubic metres of voids per hectare. Such voids may be created preferentially at times
