Fragipan Horizon - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 150

Fig. 15.1 A fragipan
(30-50 cm depth) in an
Alfic Fragiorthods, Upper
Peninsula, Michigan
(Photo by J. Bockheim)
Grossman and Carlisle ( 1969 ) reported depths to the surface of the fragipan as
ranging between 25 and 100 cm and the thickness from 15 to 125 cm. The surface of
the fragipan in northern MI ranged from 20 to 50 cm and thickness ranged from
15 to 60 cm (Yassaglou and Whiteside 1960 ).
In the majority of pedons, the fragipan contains a weak to strong coarse or very
coarse prismatic structure, sometimes breaking down to a platy structure or to
blocks. The interiors of the prisms often are massive. When viewed horizontally
and vertically, the inter-prism areas often are bleached, lighter in color, and display
redoximorphic features. The fragipan horizon generally has a firm or very firm
moist consistence. The reversibility of the cementing of the fragipan can be readily
observed in the field. When the soil is moist, the fragipan is easily excavated,
but digging becomes very difficult after sustained dry periods in late summer.
The brittleness that is commonly mentioned in soil descriptions reflects sampling
during drier periods, at which time the fragipan breaks with a characteristic snap.
Many fragipans are also argillic horizons and show evidence of clay movement,
including argillans, pore infillings, and in coarse-textured soils, bridging of sand
and silt grains.
Limited soil physical data are available for soils with fragipans in the NRCS
databases. One of the key physical properties of the fragipan is a high bulk density,
which commonly ranges from 1.7 to 2.0 g cm 3 (Table 15.1 ) and severely reduces