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| Titel |
Mapping erosion at field scale in Wallonia |
| VerfasserIn |
Nicolas Feltz, Alexandre Maugnard, Hélène Cordonnier, Charles Bielders, Abdel Ilah Mokadem |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051103
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| Zusammenfassung |
| According to the European legislation, each country must identify fields at high risk of
soil erosion in order to fight against this land degradation process. The aim of this
study was to assess the actual erosion rate for every agricultural field in Wallonia
(Belgium). For this purpose, the Revised Universal Soil Loss Equation (RUSLE) was
selected given its ability to be integrated in a geographical information system (GIS)
and its simplicity, which makes the results easy to understand by non-scientific
end-users.
In RUSLE, the mean long term annual soil loss E [t.ha-1.y-1] is
estimated as the product of 5 factors (Eq. 1, Wischmeier and Smith,
1978)1:
E = R -
K -
LS -
C -
P [Eq. 1]
Three of these factors (rainfall erosivity R [MJ.mm.ha-1.h-1.y-1], soil erodibility K
[t.h.mm-1.MJ-1], topography LS [-]) are available as GIS data or easily derived from
existing data. Cover management factor C [-] was determined from field measurements for
the most common rotations in Wallonia. In this study, specific practices that aim at limiting
erosion aren’t considered and the P factor (support practice factor [-]) is assumed to be equal
to 1.
Experimental determination of the C factor (Eq. 2, Yoder et al.,
1997)2
requires measuring many field characteristics.
C = --(SLR-
EIn)
EItot with SLR = PLU -
CC -
SC -
SR -
SM [Eq. 2]
where EIn is rain erosivity for the period of interest.
In this study, only parameters affecting the canopy cover (CC [-]), surface cover (SC [-])
and soil roughness (SR [-]) sub-factors were determined, since prior land use (PLU [-]) and
soil moisture (SM [-]) sub-factors include too many parameters that are virtually impossible
to determine at a regional scale. Plant height, leaf cover, residue cover and soil roughness
were measured once every two weeks for Wallonia’s main crops (sugar beet, potatoe, maize,
flax, wheat, barley, spelt and rapeseed) during an entire crop cycle. On average, five fields of
each crop were monitored in each of 4 agro-pedological regions of Wallonia. These data
were then aggregated to compute average soil losses on every agricultural plot of
Wallonia.
Without considering land use (C = 1), the north of our study area shows lower erosion
rates than the south. This can be explained by both rainfall erosivity, that can be more than 4
times higher in the south, and topography, which is quite flat in the north but hilly in the
south. LS factor is thus higher in the south, even though average plot size is lower, because
the slope has an important weight in its calculation.
Experimental determination of the C factor reveals major differences between crop
rotations but very few differences between agro-pedological regions. Values range from 0.33
(barley – sugar beet – wheat rotation) to 0.55 (continuous maize). These differences
highlight the important impact of crop rotations, and hence of agricultural practices, on
actual erosion rate. Grassland C factor was assumed to be equal to 0.01 (Morgan,
1995)3.
Taking into account the actual land use leads to make more homogenous soil
loss rates between north and south. Indeed, northern agriculture is intensive and
based on crop production on very large plots while, in the south, it is based on meat
production and thus mainly uses smaller grassland plots, which offsets the topographical
effect.
At present, RUSLE soil loss estimates only consider rill and interrill erosion.
On cropland, gully erosion may, however, also be a major form of erosion. Next
steps would be to integrate gully erosion and practices that aim at limiting erosion. |
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