Agriculture Reference
In-Depth Information
Gaseous
Loss
Crop
Fertilizer
Litter
Runoff
Root
Microbial
Biomass
Soil Organic
C and N
Available
C and N
Burrow
Earthworm
Plant Uptake
Stable
Aggregates
Matrix and Bypass
FIGURE 9.3
Ecosystem budget model to examine pools and Þuxes of C and N in the presence of earthworms.
Note: Bold boxes indicate pools and Þuxes in which earthworms are predicted to have a particularly signiÝcant
impact.
(Stinner et al. 1997). (Mechanisms by which earthworms inÞuence plant uptake of nutrients are
addressed further by Brown and Edwards in Chapter 2 of this volume.)
There is also a potential for N to be lost from the system through leaching. We observed
increased nitrate levels deeper in the soil (Blair et al. 1997) and increased leachate volume and
total N leaching below 45 cm in plots with increased earthworm populations relative to plots with
decreased populations (Domnguez et al. 2004). In a similar study, DON concentrations were greater
in soil leachates in plots with added earthworms than in control plots with ambient populations
(Subler et al. 1997).
The increased movement of N through the soil proÝle may be because of greater numbers of
earthworm burrows (Lachnicht et al. 1997) and greater bypass or preferential Þow. A 15-year tillage
study in Finland showed that the saturated hydraulic conductivity of soil was correlated positively
with earthworm burrows, and that deeper burrows not continuous to the surface could act as
preferential Þow paths at the topsoil-subsoil interface (Pitknen and Nuutinen 1998). It is clear that
earthworm burrows can have persistent effects on soil drainage, but a better understanding is needed
of the long-term effect of burrows on the potential loss of nutrients through leaching.
Earthworm cast production may also play an important role in system-level Þuxes of C and
N. Earthworm casts are rich in available C and N and may include anaerobic microsites; these
are conditions that favor denitriÝcation (Svensson et al. 1986). DenitriÝcation rates are typically
greater in earthworm casts than in surrounding soil (Elliott et al. 1990, 1991). Earthworm casts
deposited on the surface of English pastures were estimated to contribute from 12 to 26% of
total denitriÝcation in those pastures (Knight et al. 1992). We found that denitriÝcation rates in
middens of
, which include a mixture of surface litter and earthworm casts, were
four to ten times greater than in surrounding bare soil and could contribute up to 20% of total
denitriÝcation in a corn agroecosystem (P. Bohlen, unpublished data). Although denitriÝcation
L. terrestris
 
 
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