Dense and Cemented Horizons: Fragipan and Duripan
Pans are dense or cemented pedogenic soil horizons that obstruct root penetration and movement of air and water. Hard or dense layers of geological origin are not considered pans. Examples of non-cemented, dense pans are plowpans, found at the bottom of the Ap horizon and fragipans. Examples of cemented pans are humus pans (Chapter 11), petroferric horizons (Chapter 13), thin ironpans (placic horizons) at the contact between hydromorphic surface horizons and aerated subsoils (Chapter 7), iron concretion horizons at the basis of a puddled layer in wet rice cultivation, (petro)calcic and (petro)gypsic horizons (Chapter 9), B horizons of hydromorphic podzols, and duripans. Dense pans slake in water, while cemented pans do not. In the following, only the fragipan and the duripan will be discussed. Both fragipans and duripans are diagnostic horizons in the USDA soil classification, and appear as phases in the FAO Legend.
KeywordsSaturated Hydraulic Conductivity Soil Survey Staff High Bulk Density Drey Climate Arid Soil
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