01860naa a2200289 a 450000100080000000500110000800800410001910000180006024501120007826000090019052010930019965000110129265000190130365000190132265000120134165000120135365000120136565000220137765000230139965300140142270000160143670000240145270000180147670000150149470000130150977300480152215550572000-02-16       1999    bl ---       0--  u    #d1 aWESTERHOF, R.  aAggregation studied by laser diffraction in relation to plowing and liming in the Cerrado region in Brazil.  c1999  aIn the Cerrado savanna region in Brazil, the effects of different land use on Oxisol aggregation were studied, using laser diffraction grain size analyses. The topsoil of plowed systems had significantly lower amount of  macroaggrehates (2000-194 um) and a significantly higher amount of soil in the microaggregate size and and primary particle fraction (&lt76 um) compared to pastures and the native Cerrado. In plowed systems low in soil organic carbon (SOC), lime had a negative effect on aggregate stability. Lime addition had no effect on topsoil aggregation in land use systems that were not plowed regularly  and generally had SOC content. For all the studied topsoils, pHKCl was positively correlated with the amount of clay dispersed after 3 h of shaking in water. SOC did not influence clay dispersion in the range of soils studied. In continuous cropping systems in the Cerrado region, with a combination of mechanical  stress and low SOC, liming will cause an increase in small aggregates and primary particles and hence contribuite to a destabilization of 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.  tGeoderma, Amsterdamgv.90, p.277-290, 1999.