The purpose of this study was to investigate the results of two long-term fertilization experiments on soil organic C, total N, and mineralizable N in the Jiangsu Province of People's Republic of China. The soil samples that received manure over the years contained more soil organic C, and total N than the inorganic fertilized samples. Soil organic C was closely correlated with total N and there were correlations between crop yields and soil organic C contents and between crop yields and soil total N contents. Plant-available N was estimated using biological and chemical tests. Mineralized N formed under anaerobic incubation was low except for those soil samples that received manure. Microbial biomass C and N were estimated using the chloroform fumigation-incubation method (CFIM) and fumigation-extraction procedures. Biomass measurements by CFIM were more precise and reliable than values obtained by fumigation-extraction. Treatment differences in biomass were not significant. Estimates of biomass C and N were influenced by the choice of the control soil and the period of incubation used by the CFIM. Unfumigated (10-20 d) control soils were found to be the best control for samples. Extraction of mineralized N using O.5M NaHCO$ sb3$ after incubation overestimated biomass N since this extraction was found to extract non-biomass N.

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