Agriculture Reference
In-Depth Information
decomposing litter under freshly fallen leaves (Figure I.42); and (iii) active exportation
by anecic earthworms or termites to, respectively, the drilosphere or termitosphere (see
Sections IV.4 and 5). Decomposing material is leached into the soil where it is flocculated
and precipitated in contact with permanent-charge clay minerals and sesquioxides
(Toutain, 1981; Duchaufour, 1982) (Figure IV.24).
In an English pasture, 20 years of pesticide (phorate) application eliminated earth-
worm populations. This resulted in a dramatic increase in bulk density, shear strength,
penetrability and depth of leaf litter, but greatly reduced soil organic matter content, pH
and soil moisture content (Clement
et. al.,
1991).
2.5.3
REGULATION OF MINERALISATION BY INVERTEBRATES
Invertebrates usually have limited direct impacts on mineralisation. In contrast, their
indirect effects on microbial activities through,
e.g.,
grazing and mechanical litter trans-
formation litter may be far more important. Verhoef and Brussaard (1990), for example,
estimated the approximate contribution of fauna to nitrogen mineralisation to be 30 %,
over a range of natural ecosystems and agroecosystems. However, microbial activity
may be inhibited for long periods in the faecal pellets of certain invertebrates.
Changes in mineralisation rates
Digestion generally results in the direct assimilation by invertebrates of 5 to 50 % of
the ingested litter (Bocock, 1963; Petersen and Luxton, 1982; Dickschen and Topp,
1987; Deleporte, 1987). However, faecal pellets egested by the saprophagous macro-
and mesofauna may be resistant to degradation and accumulate to form a progressively
increasing proportion of the H layers in moder litter systems (Kubiëna, 1953; Rusek,
1985; Toutain, 1987b). Invertebrate feeding thus significantly accelerates decomposition
in comparison with situations where these animals have been eliminated by such
techniques as naphthalene exclusion (Crossley, 1977). Removal of the fauna from
