This paper reports the surplus-deficit distribution of organic carbon (0.C.) in soil obtained through a 4-year field experiment with different treatments of fertilization.Results show that there was severe deficit in the balance of soil organic carbon without fertilization,which caused the produce of loosely combined organicmineral complexes and lowly condensed humus.Application of chemical fertilizer alone temporarily kept higher productivity of soil and lost not much of organic carbon in soil.The loss of O.C.under this condition mainly came from the appearance of the stably and tightly combined organic-mineral complexes and highly condensed humus.Even though there was a decrease of total soil O.C.,because of the compensation of crop residues naturally returned to field,there still was surplus of loosely combined O.C.little loss of fulvic acid and a great loss of humic acid and humin were observed in this case.It seems that fertilizer actually promoted the renewal of soil humus and resulted in less undesirable influence on soil complex and nutrient-supplying ability in a short time.There was surplus balance of soil O.C.in field when organic materials were combined with chemical fertilizers.Large amount of manure applied in field made the surplus O.C.almost averagely distributed among loosely,stably,and tightly combined complexes.However,the increase of soil O.C.still could not markedly improve the activity of humus.The accumulation of O.C.was mainly in the form of fuvic acid distributed among loosely combined organicmineral complexes when straw was added.This promoted the activity and cycle of soil humus,and enhanced the property of nutrient supply capacity.