Three treatments were tested on a warm (July) and a cold (March) sampling dates for the determination of in situ inorganic nitrogen of surface soil in the Fushan hardwood forest. The commonly used KCI solution was applied as the extraction solution on 3 separate occasions before the determination. According to the results, immediate extraction of soil samples gives the best estimation of NO3(superscript -)-N, NH4(superscript +)-N, and total inorganic N concentrations in soil. Keeping soil samples in the extraction solution and quickly sending them back to the laboratory can produce values close to those of field extraction. This is better than those staying overnight, then being transported, and extracted in the laboratory. Deviations from the estimation by in situ extraction are more serious in the warm than in the cold season. Therefore, immediate field extraction is recommended for determination of in situ inorganic nitrogen.