01951naa a2200241 a 450000100080000000500110000800800410001902400560006010000170011624500990013326000090023252012920024165000090153365300110154265300120155365300260156565300080159170000160159970000160161570000190163170000180165077300410166820257202016-02-01       2015    bl uuuu     u00u1 u    #d7 ahttp://dx.doi.org/10.1016/j.catena.2015.06.0162DOI1 aRAMOS, M. R.  aClay mineralogy and genesis of fragipan in soils from Southeast Brazil.h[electronic resource]  c2015  aFragipan horizon has a hard consistencywhen dry but is brittle when moist. Such a horizon restricts root growth and water infiltration due to the low volume of macropores and discontinuous voids. In Rio de Janeiro state in Brazil, neighboring soils were developed from different materials (sediments and granite/gneiss) and were subject to the same environmental conditions; one manifested fragipan characteristics in the subsurface and the other did not. The main objective of this study was to characterize and quantify clay minerals and relate their properties to the genesis of fragipan horizons. The fragipan in the studied soils show high bulk density (1.67 g cm?3) and low average macroporosity (0.03 cm cm?3), total porosity (0.42 cm cm?3) and hydraulic conductivity (1.43 cm h?1). Sequential and interrelated causes favored the formation of fragipan horizons: 1) face to face adjustment of kaolinite (Ka) filling of larger spaces occurring between sand grains, favored by low goethite contents and the absence of hematite and gibbsite; and 2) mineral binding and cementation of sand, silt and clay fractions by amorphous materials. Higher amounts of goethite and lower amounts of amorphous materials in the clay fraction were associated with horizons with higher total porosity.  aSolo  aBrasil  aGênese  aMineralogia de argila  aSul1 aMELO, V. F.1 aUHLMANN, A.1 aDEDECEK, R. A.1 aCURCIO, G. R.  tCatenagv. 135, p. 22-28, Dec. 2015.