Geoscience Reference
In-Depth Information
But at this stage of observation, a third hypothesis is compatible
with the facts. We can think that the layer of sand is the residue
from chemical decomposition, or mechanical removal, of the
clay. The little sand that the clay contains is concentrated in
place until it alone survives. In support of this new hypothesis,
it is 'observed' that clay has already disappeared in the upper
slope from some pockets. In the
sandy front
it has been almost
completely eliminated. Here it only survives in some volumes
on the way to reduction.
One may, therefore, hesitate to choose between uphill invasion by
the sand and downhill invasion by clay. In practice, a lot of other
information is collected in order to decide between various hypotheses.
For example, does the clay contain sufficient sand to explain the possible
concentration of the latter? Is it the same sand on both sides of the
boundary, and so on? It is clear that morphological observation, essential
for posing such problems, is not sufficient for solving them.
Be that as it may, the above example shows that there are
transformation
fronts
in many soils. Pedological volumes are formed at the expense of
some others. This is observed time and again in the tropical environment
where the weathering phenomena are pronounced and last long, which
makes them at least visible, if not evident. In temperate or cold climate,
as we will demonstrate later, things happen in the same way, but are
less evident.
As emphasized above, uncertainties are part of observations
in situ
.
Some scientists are detached from reality and only consider laboratory
experiments conducted on 'soil extracts' as supreme. The environment,
though, indisputably carries important information, particularly on soil-
environment relations. For example, to see a thousand times Podzols
under rhododendrons (Chap. 11) demonstrates better than all research
station experiments that this vegetation is favourable for podzolization.
The field naturalist does not have to be ashamed for his empiricism.
There are instances when observation is by far the best method… It
is still necessary to know how to do it. Soil mapping, which requires
understanding of the distribution of soils in order to describe it by
accounting for it through a pattern, is a good method for learning to
see (Legros 2006).
Sometimes, in nature, we find situations in which all the pedogenetic
factors are constant but for one that varies. For example, under constant
Soil-environment relations
