IDENTIFICATION AND PROPERTIES OF FRAGIPAN SOILS IN THE PIEMONTE REGION OF ITALY

The presence of a fragipan horizon in the soil profile restricts plant growth and limits nonagricultural uses. This is of special concern in the Piemonte region, in northwestern Italy, where the soil of numerous areas is reported to have a fragipan. Four sites were selected for this study with the aim of ascertaining the presence in the profile of a horizon that meets the criteria for a fragipan. In addition to standard morphological observations and physical analyses, Hg intrusion porosimetry and image analysis of thin sections were used to help in fragipan characterization. The pan of all four sites showed a suite of characteristics such as coarse prismatic primary structure, prominent vertical mottling, extremely hard dry consistence, brittleness, and absence of roots that indicated the presence of a fragipan. Other pedogenic features, e.g. clay films, mangans, ferrans, and concretions, were observed in the field. Although some of the Bx horizons had a clay content slightly higher than prescribed, in general textures were within the range prescribed for fragipans, as were bulk densities. Mercury intrusion showed a decrease in total porosity with depth, residual pores becoming dominant over storage and transmission pores in the fragipans. Image analysis of thin sections revealed a decrease of elongated pores and the presence of vesicles and compound packing voids. Also, oriented clay coatings within the pores and mangans and ferrans were observed in the fragipan. Pore-size distribution and pore shape appeared to be useful in characterizing the fragipan.