Saturday, 15 July 2006

Soil Functional Capability Classification Map of the World.

Sonya Ahamed1, Deborah Balk1, Rafael Flor1, Marc Levy1, Cheryl Palm1, Pedro Sanchez1, Adam Storeygard1, and Stanley Wood2. (1) Columbia University, 61 Route 9W, P. O. Box 1000, Palisades, NY 10964, (2) IFPRI, 2033 K Street NW, Washington, DC 20006

The soil fertility capability classification system (FCC), first introduced by Stanley Buol and coworkers in 1975 is a technical system to interpret soil taxonomy and additional soil attributes in ways directly relevant to plant growth. The most recent update (version FCC4, Sanchez et al,Geoderma 2003)identifies four topsoil and four subsoil texture types as well as 17 condition modifiers defined to quantitatively delimit the soil's capacity to provide ecosystem functions and services. Since the system is now interpreted beyond soil fertlity, we now call it Soil Functional Capacity Classification, while retaining the original acronym FCC.

Drawing on earlier efforts, a computer program was written to create raster files depicting the global distribution of soils assigned the condition modifiers and soil types outlined in FCC4. The FAO Digital Soil Map of the World and the USDA Soil Moisture Regimes (SMR) and Soil Temperature Regimes (STR) were used as input data, and the resulting maps are at .08333 degree resolution. In the maps depicting soil moisture stress and low soil temperatures points on the globe were assigned a value of 0 or 100 based on the categories used in the SMR and STR datasets. The other maps are based on data from the Soil Map of the World and show the percentage of each FAO mapping unit that has one or more FCC attributes. These percentages were determined by the constituent soil units based on the 1974 legend of the Soil Map of the World, as well as by the slope classes, texture types, and phase of each mapping unit. The soil attribute dataset “Soil Parameter Estimates for the Soil Types of the World for Use in Global and Regional Modeling” (ISRIC/IFPRI 2003), also referred to as WISE-2, was used to make a preliminary determination of which soil units met the physical/chemical definition for the modifiers for which attribute data was available. The results were then supplemented byseveral iterations of expert opinion.If there was no attribute data available for a particular modifier, the soil units were solely determined using expert judgment. Using such taxotransfer functions we were also able to identify soil units assigned more than one modifier and to map these combinations as percentages of each mapping unit.

We present maps of eight FCC classes and 16 modifiers as well as maps displaying areas with particularly adverse combinations of two or more modifiers. Mapping the extent of these soil functional attributes on a global scale using the best available data offers soil scientists and policymakers an important tool in understanding and managing soil resources.

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