The typical black soil (Mollisol)

the most fertile and productive soils distributed in Northeast Chi- na

was subjected to conversion from prairie-grass vegetation to cropland

resulting in deteriorative changes of soil properties after reclamation a century ago.To examine the impact of land management practices on soil organic carbon (SOC) pools and aggregate stability of rhizospere soils

we determined SOC in whole soil and various size aggregates from two long-term experiments (16

20 a).The soil management systems were grassland (GL) and croplands which had four treatments:continuous maize (CM)

continuous soybean (CS)

continuous wheat (CW)

and rotation system (RS).SOC content in rhizosphere soil decreased in the order of GL>CS>CM>RS>CW

while the total soil nitrogen showed an order:GL>CS>CM>CW>RS.SOC content of GL increased by 7.8% as compared to the average of croplands after 20 years of natural vegetation restoration.The percentages of water-stable aggregate (>0.25 mm) (WSA_(>0.25mm)) de- creased in the order:GL>CM>RS>CS>CW in the rhizosphere soil.WSA_(>2mm)

the most important fraction for C storage in GL

accounted for 39.0% of the whole soil.A significant positive correlation was found between C stored in WSA_(>0.25mm) and total SOC (r=0.89

p<0.05)

and between the mean weight diameters (MWD) of aggregates and C stored in WSA_(>2mm)(r=0.99

p<0.01).Root density was found to significantly correlate with WSA_(>0.25mm)

WSA_(>2mm) and MWD at p<0.05 or p<0.01

respectively.In con- clusion

root system played a vital role in formation and stability of soil macroaggregates.