02413naa a2200349 a 450000100080000000500110000800800410001910000190006024501160007926000090019552014820020465000150168665000180170165000150171965000130173465000130174765000120176065000170177265000220178965000150181165000130182665000150183965000180185465300180187265300200189070000150191070000170192570000170194270000150195970000210197477300680199515651132002-08-29       2002    bl ---       0--  u    #d1 aBALBINO, L. C.  aChanges in porosity and microaggregation in clayey Ferralsols of the Brazilian Cerrado on clearing for pasture.  c2002  aFerrasols have a macrostructure that is weak to moderate and a strong microstructure consisting of near spherical microaggregates. We have studied the evolution of the structure under changing land use in two Ferralsols under a native Cerrado and under pasture after recent clearing by measuring bulk density. We studied the microaggregates characteristics and resulting porosity using scanning electron microscopy and mercury porosimetry, respectively. Microaggregates 50-300 um in diameter are attributed to termites. They were in a much closer arrangement from the surface to 1 m depth under pasture than under Cerrado. Larger microaggregates, 500-1000 um in diameter, that are closely packed, resulted from earthworm activity. They were more numerous under pasture than under Cerrado. Thus within a few years, clearing and grazing have caused a dramatic decrease in microstructure that is one of the rare favourable characteristics of Ferralsols of agriculture. This evolution that affects the subsoil to 80-90 cm cannot be attributed to compaction by mechanical deforestation alone but seems to result from a change in the faunal activity in the faunal activity in the soil. Finally, the packing of the clay particles within the microaggregates was similar whatever the type microaggregate and land use. Our results accord with ealier studies showing that the porosity resulting from clay packing varies little in Ferralsols in which the fine material is mainly kaolinite.  aclay soils  adeforestation  aFerralsols  apastures  aporosity  aCerrado  aDesmatamento  aEstrutura do Solo  aFerralsolo  aPastagem  aPorosidade  aSolo Argiloso  aLand clearing  aSoil structures1 aBRUAND, A.1 aBROSSARD, M.1 aGRIMALDI, M.1 aHAJNOS, M.1 aGUIMARAES, M. F.  tEuropean Journal of Soil Sciencegv. 53, p. 219-230, Jun. 2002.