Agriculture Reference
In-Depth Information
P
ROBLEMS
OF
S
CALE
Because biological organisms interact not only with each other, but also with soil physical properties
(mainly the soil pore systems), it is necessary to describe the spatial distribution of each and to
establish if their specific distributions can be considered independently. Functional links between
living organisms and soil pore systems can occur at any scale, to such an extent that it is not
possible to consider, at any place in the soil profile, the whole range of scales at which these
interactions take place (i.e., ranging from microns to centimeters). Observation techniques are
unable to deal with such a wide range; it is then necessary to develop a technical series in which,
in the same sample, soil organization can be observed in such a way that the different levels of
scale can be related to each other. It is possible to take large undisturbed soil cores (150- to 200-
mm diameter) and describe them with a CAT scanner at a resolution of 1 mm (Joschko et al. 1991;
Daniel and Kretzschmar 1997). The same core could be impregnated and cut into 2-mm slices from
which x-ray images can be taken at a resolution of 500 to 300 Hm. Finally, the faces of these slices,
once polished, could be observed under a microscope at a resolution of 50 to 30 Hm (Vogel and
Kretzschmar 1996). At any scale, specific models can be designed for an analysis of the pore system
properties and their interactions with distributions of living organisms and activities (Monestiez et
al. 1993; Krebs et al. 1994; Vogel and Kretzschmar 1996).
CONCLUSIONS
I
NTERACTIONS
BETWEEN
E
ARTHWORMS
AND
S
OIL
F
ORMATION
As biological functions and physical properties interact, with the distribution and the seasonal
variations in earthworm burrow distributions, earthworm burrows are seen as part of the develop-
ment of soil organization, which is a characteristic of soils under given climatic, relief, and parent-
rock conditions (Dokuchaev 1883). DokuchaevÔs definition of soil genesis fixed the context of soil
typology. The scientific literature has been generous in topics and articles on soil-forming factors
without any definite improvements of DokuchaevÔs statement. From the interactions between
factors, soil organization is derived as a concept for the soil geometrical, functional, and topological
properties.
Babel et al. (1995) proposed an interesting definition of soil fabrics that is based on soil
morphological features. They described soils based on three characteristics: place, pathways, and
boundaries. These characteristics are attached to each object or function and are valid at any scale.
It is probable that these characteristics would perfectly fit the description of the interactions
addressed here. Soil-forming factors would be replaced by soil-forming interactions, for which
places, pathways, and boundaries would be attached to geometrical, functional, and topological
properties of these interactions, respectively.
M
ONITORING
I
NTRODUCTIONS
OF
E
ARTHWORMS
TO
N
EW
S
ITES
The rationale of the intentional introduction of earthworms is based on an assumption of a
beneficial effect of earthworms on soil fertility. However, transplanted species cannot always be
expected to behave as they did in their original habitat. Earthworm activities should be regarded as
dependent on soil organization in the same way that the density dependence of predatorÏprey rela-
tionships is described. In other words, these activities could not be understood without the ability to
identify the specific interactions that take place in a given location (native habitat or introduction
area). The question of reactions of soil organization to earthworm introductions should be regarded
in terms of soil dynamics equilibrium: Will the introduced earthworms be able to change the charac-
teristics of the actual organization of soils where they are introduced to such an extent that they bring
about a new equilibrium, that is, a new state of organization involving and relying on a new set of
