World Soil Reference Collection

The soil reference collection of ISRIC is unique in the world and was built up to show representative examples of the units distinguished in the legend of the soil map of the world. These reference profiles – or soil monoliths - would be well documented and analysed and therewith be an example and a resource for education, correlation and research.

Soil monoliths are undisturbed, vertical soil samples of about 1.5 m depth. They present the soil very close as to how they are seen in a profile pit in the field, with the layering, colours and structure of the soil. The collection has over 1100 soil monoliths from around 82 countries in the world. The collection represents a wide range of geographic areas and environments, soil types, soil processes and human impact on soils. A reference profile is fully documented (description and images from the field), fully analysed and additional sampling materials are available for each of the soil horizons for relevant future research. The collection is considered a cultural world heritage collection.

The reference collection of soil samples from the reference profiles described in the ISRIC Soil Information System (ISIS) database, which is part (a schema) of the World Soil Information Service (WoSIS) since 2016, have been fully analyzed by standard methods.

Maintenance of the data, completion of analytical data, and gradual expansion of the collection remains an important task but emphasis will shift to use of the data, verification for applications, and data generation by pedotransfer functions. Samples from ISRIC's World Soil Reference Collection have been provided to various research groups for specialized studies, such as:

• Evaluation of the ability of mid-infrared diffuse reflectance spectroscopy (4000–602 cm-1) to predict chemical and textural properties for a globally distributed soil spectral library by ICRAF, Kenya

• Spectral reflectance based indices for soil organic carbon quantification by Wageningen University and Universite Catholique de Louvain, and

• Model development for estimating clay content from the water content of soils of different clay mineralogy by Aarhus University, Denmark

The ISRIC soil reference collection has full field description of soil and site conditions and samples of soil horizons have been analyzed for chemical and physical characteristics. A current project analyses the reference samples for soil biological parameters. A total number of 4658 samples for soil DNA from about 63 countries and sampled in different moments in time between 1952 and 2016. Read more about the assessment of soil DNA of the ISRIC World Soil Reference Collection here.