Agriculture, Ecosystems and Environment 83 2001 83–94
The impacts of land use policy on the soil erosion risk: a case study in central Belgium
Anton J.J. Van Rompaey
a,∗,1
, Gerard Govers
a,2
, Etienne Van Hecke
b
, Kristine Jacobs
a
a
Laboratory for Experimental Geomorphology, Catholic University Leuven, Redingenstraat 16, B-3000 Leuven, Belgium
b
Institute for Social and Economic Geography, Catholic University Leuven, de Croylaon 42, B-3001 Leuven, Belgium Received 25 August 1999; received in revised form 31 January 2000; accepted 27 April 2000
Abstract
Set-aside programs of the European government have a double impact on the regional soil erosion risk in agricultural regions: 1 there is less area susceptible to soil erosion and 2 fields with a high erosion rate are preferably taken out of
production resulting in a decrease of the average erosion risk. In order to quantify this double effect an inquiry among farmers in central Belgium was set up to find out which fields are preferably taken out of production. A statistical analysis pointed
out that fields with a weak slope gradient, a loamy topsoil and good soil drainage have a low probability of being taken out of production. The results of the questionnaire were used to construct a transition probability map representing for each field
the probability that it will be taken out of production. These transition probabilities were used to simulate the decrease in regional erosion risk for different scenarios. The outcome of these simulations suggests that there is a negative power relation
between the set-aside percentage and the regional soil erosion risk. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Soil erosion; Land use changes; Set-aside; EU-CAP; Belgium
1. Introduction
The potential for surface runoff and soil erosion is very much affected by land use and cultivation. There-
fore, the modelling of land use changes is important with respect to the prediction or soil degradation and
its on-site and off-site consequences.
∗
Corresponding author. Tel.: +32-16-32-64-11; fax: +32-16-32-64-00.
E-mail address: anton.vanrompaeygeo.kuleuven.ac.be
A.J.J. Van Rompaey.
1
Research Assistant of the Fund of Scientific Research F.W.O., Flanders.
2
Research Director of the Fund of Scientific Research F.W.O., Flanders.
Many land use change studies have shown that almost all land use changes are clearly driven by hu-
man activities e.g. Turner et al., 1990; De Koning et al., 1998; Thornton and Jones, 1998. Potential
land use change drivers are, for example, population growth, urbanisation, industrialisation and the devel-
opment of a global economy. Regional, national or supra-national policy-makers translate these driving
forces into land use regulations. Therefore, land use changes are often policy driven. However, the bio-
physical conditions of the land, such as soil character- istics, climate, topography and vegetation determine
to a large extent the spatial pattern of land use and land use changes. The interaction of land use change
drivers with the biophysical environment takes places at the level of the land users. The importance of their
0167-880901 – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 0 0 0 0 1 7 3 - 0
84 A.J.J. Van Rompaey et al. Agriculture, Ecosystems and Environment 83 2001 83–94
behaviour and decision rules in response to land use change drivers has only recently been recognised
Veldkamp and Fresco, 1996. A good example of this principle is the Common
Agriculture Policy of the European Union EU-CAP. Since the reform of the EU-CAP in 1992, the support
system for European farmers has thoroughly changed. The new CAP includes regulations on set-aside in
order to control the level of agricultural production and to secure the income of farmers. Therefore, these
EU-CAP rules can be seen as a land use change driver. The farmers are financially supported by EU
relative to the area of set-aside land on their farm. Set-aside land is land that is either fallowed or used for
non-food crops, e.g. energy crops. In the new support arrangements the farmer has to set aside a minimum
percentage of his land, based on his area of arable land in 1991. EU changes the minimum set-aside per-
centage from year to year depending on the market situation. Since 1992 the minimum set-aside percent-
age has varied between 5 and 15 see Table 1. The take-out period, during which production for agri-
cultural purposes is forbidden, runs from 15 January until 31 August for a given year. Protection by vege-
tation of the fallow fields with selected fallow-species is obligatory: however, the fallow species are specific
for each EU-member state Sibbesen, 1997.
As the potential for surface runoff and soil ero- sion is very much affected by land cover, these CAP-
regulations potentially have a very strong impact on the average soil erosion rates in agricultural regions.
A permanent vegetation cover protects the soil from direct raindrop impact, crusting and sealing which
reduces the amount of surface runoff till almost zero.
Table 1 Minimum set-aside percentages since the reform of the Common
Agriculture Policy of the European Union Year
Minimum set-aside percentage
1992 15
1993 15
1994 15
1995 12
1996 10
1997 5
1998 5
1999 10
De Ploey 1989 estimated that soil erosion rates on unprotected fields may be 100–1000 times higher than
on fields with permanent vegetation cover. Therefore, it may be expected that a fallow percentage of, for
example, 10 will reduce the total amount of soil erosion by 10 since soil erosion on the protected
fields may be reduced to 0 Mg ha
− 1
per year. This is indeed true if farmers select at random fields for
set-aside. However, if farmers prefer to take steep and erodible fields out of production the reduction
of the total erosion rate will be much higher since the average soil erosion risk of the remaining fields
will be lower. Thus, insight in the decision rules that farmers use in response to the CAP-regulations is
necessary to estimate the magnitude of the effects of the new policy on soil erosion in agricultural
regions.
The objectives of this study are: 1 to determine what field properties do farmers take into account
when selecting parcels for set-aside; 2 to model and simulate the spatial pattern of set-aside fields under
different scenarios of the EU-CAP, and 3 to quan- tify the impact of different set-aside scenarios on the
regional soil erosion risk.
2. Materials and methods
