02027naa a2200301 a 450000100080000000500110000800800410001910000180006024501260007826000090020430000130021352010730022665000110129965000190131065000190132965000120134865000120136065000120137265000220138465000230140665300140142970000160144370000240145970000180148370000150150170000130151677301960152915453991999-07-15       1999    bl uuuu     u00u1 u    #d1 aWESTERHOF, R.  aAggregation studied by laser diffraction in relation to plowing, soil organic matter, and lime in the Brazilian cerrados.  c1999  ap.64-76.  aIn the Cerrados, a large savanna region in Brazil, the effects of different land use on aggregation in Oxisols were studied, using laser diffraction grainsize analysis. The topsoil of plowed systems had significantly fewer macroaggrehates (194-2000 um) and a significantly larger fraction of microaggregates and primary particles (&lt76 um) than did pastures and native savanna. In plowed systems that were low in soil organic carbon (SOC), lime negatively affected aggregate stability. Lime addition had no effect on topsoil aggregation in land-use systems that were irregularly plowed and generally had a higher SOC content. For all the studied topsoils, pHKCl was positively correlated with the amount of clay dispersed after 3 h of shaking in water. Soil organic carbon did not influence clay dispersion in the range of soils studied. In continuous cropping systems in the Cerrados, a combination of mechanical stress, low SOC, and liming will increase the number of small aggregates and primary particles and hence contribuite to destabilizing the soil structure.  aliming  aorganic matter  asoil structure  aAradura  aCalagem  aCerrado  aEstrutura do Solo  aMatéria Orgânica  aPloughing1 aBUURMAN, P.1 aGRIETHUYSEN, C. van1 aAYARZA, M. A.1 aVILELA, L.1 aZECH, W.  tIn: THOMAS, R.; AYARZA, M.A., ed. Sustainable land management for the oxisols of the Latin American savannas: dynamics of soil organic matter and indicators of soil quality. Cali: CIAT, 1999.