Agriculture Reference
In-Depth Information
Functional Groups
Spatial Distribution
Time
Structure
HOURS
GUT CONTENT
DAYS/WEEKS
FRESH CASTS
MONTHS
AGING CASTS
YEARS: DECADES
SOIL PROFILE
Effect on
SOM
ASSIMILATION
COMMINUTION
NUTRIENT
RELEASE
PHYSICAL
PROTECTION
ACCELERATION
OF TURNOVER
Activation
of mineralization
Transfers
Conservation
FIGURE 8.3
Effects of earthworm activities on SOM dynamics at different scales of time and space.
scales of decades and hectares (Jenkinson and Rayner 1977; Molina et al. 1983; Parton et al. 1988;
Agren et al. 1991). A few papers have already described the effects of earthworms at the scales of the
different biotic and abiotic parameters with which they interact, such as (1) selection of ingested
particles and digestion processes at the scale of a gut transit (0.5 to 20 hours) (Lee 1985; Barois and
Lavelle 1986); (2) immobilization-reorganization of nutrients in fresh casts (1 to 20 days) (Syers et
al. 1979; Lavelle et al. 1992; Lopez-Hernandez et al. 1993; Tiunov et al. 2001); and (3) evolution of
SOM in aging casts (3 to 30 months) (Martin 1991; Lavelle and Martin 1992; Blair et al. 1994;
McInerney et al. 2000). Long-term evolution of SOM at the scale of the whole soil profile and
pedogenesis during periods of years to centuries has been identified, although little information is
currently available (Figure 8.3).
This chapter describes the effects of earthworms on larger-scale SOM and nutrient dynamics
observed in 3-year field experiments and details three subprocesses that may determine the long-
term effects of earthworms on soils: feeding behaviors, patterns of horizontal distribution, and
participation of earthworm activities in successional processes. Simulations of SOM dynamics,
based on the CENTURY model (Parton et al. 1988), give some insight on effects of earthworms
on soils observed at a timescale of 10 to 50 years.
EARTHWORM BEHAVIOR
Earthworm behavior may affect soil functions significantly. A major difference between short-scale
experiments and the real world is that, in confined small experiments, earthworms have limited
opportunities to choose their food and move away. This probably explains why they often lose
weight or die in laboratory experiments. On the other hand, the introduction of unrealistically high
earthworm populations to small enclosures in the field often creates concentrations of intense
earthworm activity that would not normally have occurred in the field or that concern only microsites
that are either highly dispersed in nature or infrequently visited.
S
S
P
ELECTION
OF
OIL
ARTICLES
Earthworms are known to select the organic and mineral soil components that they ingest. As a
result, their casts often have much higher contents of SOM and nutrients than the surrounding soil
(Lee 1985). This is probably because of preferential ingestion of plant residues (leaf and root litter
debris and occasionally fungi) (Piearce 1978; Ferrire 1980; Kanyonyo ka Kajondo 1984;
Bonkowski et al. 2000; Neilson et al. 2000), fecal pellets of other invertebrates (Mariani et al.
2001), and clay minerals. Barois and Lavelle (1986) demonstrated that the tropical peregrine species
Pontoscolex corethrurus
able to select either large organic debris or small mineral particles,
depending on soil type. Selection was made on aggregates rather than primary particles. However,
some earthworms may selectively ingest coarser particles than the average in soils with very high
clay contents. There is evidence that some endogeic species of earthworms ingest only aggregates
that do not exceed the diameter of their mouths, whereas other species may feed on larger aggregates
was
