Abstract: High fertility of black soils (Mollisol) is the foundation for supporting high and stable grain production in Northeast China.However,the degradation of soil quality and decline in soil fertility seriously threaten the sustainable grain production in recent years.The characteristics of changes in soil organic carbon (SOC) and nutrient content play a key role in evaluating changes in soil fertility.To access the changes in SOC and nutrients and their interactions in surface soil layer following agricultural production during the past 30 years,soil samples were collected in croplands of Hailun county,which is located in the center of typical black soil region.The data and sampling locations referred to the Second National Soil Surveys of Heilongjiang Province conducted in the 1980s.The results showed that SOC content decreased by 12% compared to that in 1981,with more carbon loss in thick layer black soil (by 22%) than in medium layer and thin layer black soils.Over the past 30 years,soil alkali-hydrolyzable nitrogen and available potassium decreased by 33% and 43%,respectively,while available phosphorus increased by 48%.Moreover,soil alkali-hydrolyzable nitrogen decreased by 3.25,2.24 and 1.64 mg·kg^-1·a^-1 in thick layer,medium layer and thin layer black soils,respectively; and soil available potassium decreased by 4.11,3.53 and 4.68 mg·kg^-1·a^-1,respectively.While soil available phosphorus content increased slightly,with an increasing rate of 0.14,0.53 and 0.22 mg·kg^-1·a^-1,respectively.The SOC was positively correlated with alkali-hydrolyzable nitrogen and available potassium,but was not significantly correlated with available phosphorus.In terms of the status of soil carbon and nutrients of black soils,agricultural management practices should be adopted,focusing on carbon sequestration,phosphorus use reduction,potassium supplementation,and nitrogen use efficiency improvement.