ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

D. OOSTWOUD WIIDENES, J. POESEN,
L. VANDEKERCKHOVE & E. DE LUNA
The effect of tillage on the stoniness of top soils
Laboratory for Experimental Geomorphology, KU Leuven,
Redingenstraat 16, B-3000 Leuven, Belgium
Many agricultural fields in the Mediterranean and elsewhere
are characterised by a high amount of rock fragments at
the surface. While this traditionally has been viewed as a
problem with respect to tillage and plant growth, recent
research showed many positive effects such as reduction of
runoff and soil erosion and enhancement of infiltration.
According to the concept of kinetic sieving the disturbance
of a mixture of particles with different diameters will result
in the largest particles moving upwards and the finest particles
moving downwards. Following this principle the
objectives of this paper were:
- to determine whether the large amount of rock fragments
of the top soils of cultivated fields in Southeast
Spain could be explained by the disturbance by tillage
and,
- to determine the number of tillage passes necessary to
reach a steady state (no more change).
Soil pits were filled with four layers (each 4 em thick) of
air-dry rock fragments, each layer containing a known distribution
of rock-fragment sizes. The pits were subjected
to different tillage frequencies by a caterpillar tractor pulling
a chisel with a duckfoot. The experiments demonstrated
that the tillage operations had a significant influence
on the vertical movement of rock fragments in the soil
profile. One series of experiments contained the coarsest
fraction at the bottom and the finest at the top of the profile
and another series showed a homogeneous distribution
with depth. For the first series the results showed that after
only two tillage passes the coarsest fraction dominated
the top layer (34 % by weight) and the finest fraction dominated
the bottom of the tilled layer (51% by weight).
Subsequent tillage increased the sorting of particles in the
plough layer but at a much slower rate. The second series
showed an even quicker rate at which large rock fragments
moved to the surface. This inverse grading may explain
the high percentage of rock fragments of top soils of cultivated
fields, especially in many parts of the Mediterranean
area where soil profiles are often shallow and stony. The
implication of this is that farmers can reduce the risk of
erosion and conserve moisture by ploughing stony soils
only one to two times under dry conditions. This practice
is relatively cheap and simple and can be easily applied in
many areas. The experiments showed that excessive ploughing
is not necessary, which is fortunate since frequent
ploughing, particularly at steep slopes, can cause serious
tillage erosion.
NATALIA 1. ORLOVA
Relief, crusts of weathering (CW)
and placers - co-evolution
All-Russian Scientific-Research Institute of Mineral Resources (Vims) 31,
Starcmonetny per., 109017 Moscou, Russia
For USSR several epochs of relief planation and CW formation
were distinguished as synchronous. But lately at last
years it was established that the ages of these both epochs
are markedly displaced as determining by different factors.
So the general surfaces of planation cannot be simply
identified with definite CW eighther for vast regions or for
large morphostructures. The profound weathering was
going «continously-intermittently» migrating at time and
place. On morphostructures with favourable climatic, tectonic
and palaeogeomorphological conditions took place
the superimposing of weathering of successive epochs and
on a whole at the same time - erosion and re-deposition of
the waste of CWo The age «sliding» of stratigraphic boundaries
is especially well expressed in comlicated transition
zones between oscillating tectonic blocks.
CW can be exploited in situ as useful deposits or can form
the parts of polygenetic placers. It can be clearly traced for
the ancient complicated placers of long formation. In several
regions there are revealed the «clusters» with CW of
profound weathering, of various types, thickness and ages.
There are various placers from exposed eluvial up to deeply
buried fluvial ones (valley and gully types). On morghostructures
where areals CW were not formed or eroded
only linear roots of CW along fractures and relatively poor
and shallow fluvial Q3-Q4 placers can usually be found.
Thus the favourable palaeoclimatic and geomorphological
conditions give the general orientation for researches of
CW and related placers; the presence of remnants of the
ancient poly-aged CW of profound weathering or shows of
their former development directly indicate on positive perspectives.
The geomorphological mapping and analyse are
important for all the scales and stages of researches. The
examples will be demonstrated.
NATALIA 1. ORLOVA 1 & MIKHAIL V. PIOTROVSKy 2
Problems of megaregional and global geomorphological
mapping
1All-Russian Scientific-Research Institute of Mineral Resources
(VIMS) 31, Staromonetny per., 109017 Moscou, Russia
2 Geological Department, Moscou State University,
119899 Moscou, Russia
Geomophological mapping remains the irreplaceable
means of information and investigation. The most effective
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