Development and use of a database of hydraulic properties of European soils

Many environmental studies on the protection of European soil and water res ources make use of soil water simulation models. A major obstacle to the wi der application of these models is the lack of easily accessible and repres entative soil hydraulic properties. In order to overcome this apparent lack of data, a project was initiated to bring together the available hydraulic data which resided within different institutions in Europe into one centra l database. This information was then used to derive a set of pedotransfer functions applicable to studies at a European scale. These pedotransfer fun ctions predict the hydraulic properties from parameters collected during so il surveys and can be a good alternative for costly and time-consuming dire ct measurement of these properties. A total of 20 institutions from 12 Euro pean countries collaborated in establishing the database of HYdraulic PRope rties of European Soils (HYPRES). This database has a flexible relational s tructure capable of holding a wide diversity of both soil pedological and h ydraulic data. As these data were contributed by 20 different institutions it was necessary to standardise both the particle-size and the hydraulic da ta. A novel similarity interpolation procedure was successfully used to ach ieve standardization of particle-sizes according to the FAO clay, silt and sand particle-size ranges. Standardization of hydraulic data was achieved b y fitting the Mualem-van Genuchten model parameters to the individual theta (h) and K(h) hydraulic properties stored in HYPRES. The HYPRES database con tains information on a total of 5521 soil horizons (including replicates). Of these, 4030 horizons had sufficient data to be used in the derivation of pedotransfer functions. Information on both water retention and hydraulic conductivity was available for 1136 horizons whereas 2894 horizons had only information on water retention. Each soil horizon was allocated to one of II possible soil textural/pedological classes derived from the six FAO text ure classes (five mineral and one organic) and the two pedological classes (topsoil and subsoil) recognised within the 1:1 000 000 scale Soil Geograph ical Data Base of Europe. Next,: both class and continuous pedotransfer fun ctions were developed. By using the class pedotransfer functions in combina tion with the 1:1 000 000 scale Soil Map of Europe, the spatial distributio n of soil water availability within Europe was derived. (C) 1999 Elsevier S cience B.V. All rights reserved.