CGMS soil suitability criteria
Introduction
The assessment of yield level at national and sub-national scale with CGMS requires information on locations and soils where the major crops are grown. This information is especially important for the spatial aggregation from simulated crop indicators from simulation units to administrative regions. Most logically, this information could be obtained by combining a European land use map and the European soil map. However, the main constraint for application of this procedure is formed by the lack of a harmonized land use map at the level of major crops. Besides, a geometric mismatch between the land use map and the soil map may contribute to inaccuracies as well. The solution found to overcome these constraints was to derive from the soil map a new map of plausible land use based on soil suitability rules. One should keep in mind that soil is not the only source of biophysical constraints for agriculture. Climate is certainly more important in some areas than soil. In CGMS, climate suitability is determined by the crop calendar table. So climate suitability is not part of the underlying study. Therefore within the analysis of soil suitability we focus on the areas where the climate is not the constraining factor. Within these areas, with suitable climates, soils could be a limiting factor to use the land. Although one should realize that crop area patterns are explained also by socio-economic and historic factors.
The aim of the present study is to define a set of soil suitability rules for each major crop group. A rule is defined by listing the unsuited classes of soil parameters, or by specifying a threshold value for a given soil parameter. The soil suitability assessment for a given crop group uses at least one but usually several soil parameters as indicators.
The present study describes the testing of a model for the assessment of soil suitability using data derived from SGDBE. We used the existing model ESCAPE, developed by INRA (Le Bas et al, 1999). ESCAPE is basically a tool offering a selection procedure for separating suited and unsuited soils (or rather soil typological units) on the basis of soil properties e.g. rooting depth, where the selection criteria can be modified by the model user. As a starting point, the selection criteria given by INRA for the following crop groups were used: grass, cereals and maize. These criteria have been regrouped in order to create new sets of systematically varying criteria and applied to the European soil data base. Each selection results in a suitability map, which was compared visually with a recent European Land Cover map (Mucher, 2004) as a plausibility check to distinguish the major agricultural areas.
