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SOIL DEGRADATION WITHIN THE SOILCRITZONE CONCEPT

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Title: SOIL DEGRADATION WITHIN THE SOILCRITZONE CONCEPT


1
SOIL DEGRADATION WITHIN THE SOILCRITZONE
CONCEPT
by
Winfried E.H. Blum and Svetla Rousseva
2
SOIL DEGRADATION SOIL LOSS - as solid material
erosion by water and wind (on erosion, there
exists an enormous amount of literature) - as
soluble matter leaching

3

4
EROSION THROUGH WATER AND WIND ARE DIFFERENT
PROCESSES
IN PRINCIPLE, THREE STEPS CAN BE DISTINGUISHED -
MOBILISATION - TRANSPORT - DEPOSITION

5
LEACHING OCCURS THROUGH DIFFERENT
PHYSICO-CHEMICAL AND BIOLOGICAL PROCESSES
- HYDRATATION - HYDROLYSIS PROTOLYSIS -
OXIDATION - COMPLEXATION IN THREE STEPS -
SOLUBILISATION -TRANSPORT - PRECIPITATION AND
FIXATION

6
WATER EROSION
USLE Universal Soil Loss Equation A R . K . L
. S . C . P A soil loss ( g.m-2 t.ha-1) R
rainfall erosivity (kinetic energy of rain) K
soil erodibility (texture, structure etc.) L
length of the slope S slope degree
(inclination) C influence of land use (type of
agriculture, forestry etc. P measures
against erosion (e.g. terracing, countour
stripping etc.

7
FORMS OF EROSION - sheet erosion - rill
erosion - gully erosion - tunnel erosion -
harvest erosion (see pictures)

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MEASUREMENT OF SOIL DEGRADATION - Recent
(actual) erosion ? Measurement on erosion plots
(on site) ? Hydrological measurements in small
watersheds by gauges
Problems - not all eroded soil material
reaches the waterways, but is deposited close
to the erosion site - extrapolation of results
from some m² to large areas is difficult or
impossible - because soil formation is a process
of thousands of years, as well as soil
degradation, actual measurements are not very
indicative for long time periods

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- HISTORICAL (PAST) EROSION
might have been quite different to the actual
one, because of different climate conditions
(climate variations in historical times)
- topomorphic approaches measurement of lake
sediments or sediments deposited downhill in
lower slope positions or in alluvial plains -
measurement of isotopes - luminescence
measurements - time markers, such as volcanic
depositions of known age in sediment
layers Exact results are in general difficult to
obtain.
- RESULTS OF LEACHING PROCESSES

mass balances based on known processes, e.g.
limestone weathering and deposition of calcrete
19

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Estimations (assessment) of soil degradation by
erosion and leaching are based on models,
extrapolating local results of measurements onto
larger areas, taking into consideration factors
such as climatic influence, landscape, soil type,
vegetation cover, land use and others (see
USLE). There are some dozen models available for
different physio-geographic regions of the world.

21
CONCLUSIONS
  1. Soil degradation is causing loss of soil
    material, counterbalancing soil formation through
    weathering of rock parent material
  2. Soil losses occur in solid (erosion) and liquid
    (leaching) form
  3. Soil losses on one site mean at the same time
    deposition of the lost material on other sites -
    through aquatic/hydraulic transport and
    deposition - through wind transport and
    deposition - through precipitation after
    mobilisation and leaching
  4. Land and soil surfaces without protective
    vegetation cover like deserts were always sources
    of soil material, whereas others were sinks,
    gaining soil material, see e.g. Sahara dust in
    South and North America

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