This research work began in 1977 and has been continued for ten years.Field experiments were conducted in the region of yellow fluvoaquic soil in north China.Data obtained showed that the increase in total carbon of soil through application of different organic manures appeared much more significant than that applied with chemical fertilizers.At the same time,the contents of various humus fractions and the amount of waterstable soil aggregates were also increased greatly by application of organic manures.The above mentioned phenomena could be observed by micro morphological characteristics of the soil.Correlations between soil treatmenu and crop yields were quite significant in spite of changes of weather conditions during the past nine years.By assuming,that the contents of humus,water-stable soil aggregates,etc.be reliable index of soil fertility,the effect of wheat straw and organic manures on crop yield are much greater than that of chemical fertilizers.