Seventeen calcareous soils representing different organic matter,total N and NO - 3-N contents were sampled from Chengcheng
,Yongshou and Yangling area of Shannxi Province, and the soils with and without leaching of NO - 3-N were used for pot experiments using wheat as indicator to discuss the relationship between initial NO - 3-N and
mineralizable N determined by various methods with wheat uptake N. The results showed that when initial NO - 3-N were not leached, soil initial NO - 3-N
extracted by KCl directly and KCl boiling method, and leached by CaCl 2 before aerobic incubation were closely related with wheat N uptake, the correlation coefficients were 0.934, 0.856, 0.862, respectively, all reached at 1% significant level. On the contrary, it was no good relationship between mineralizable N extracted by aerobic incubation, water logging method, boiling water method, alkaline permanganate extraction, acid permanganate extraction and NaOH hydrolyzation diffusion method with wheat uptake N. When initial NO - 3-N were leached, the correlation coefficient between initial NO - 3-N extracted by KCl directly and KCl boiling method, and leached by CaCl 2 before aerobic incubation with wheat uptake N were decreased greatly, and could not reach 5% significant level. However, the correlation coefficients between mineralizable N extracted by aerobic incubation, water logging method, boiling water method, alkaline permanganate extraction, acid permanganate extraction and NaOH hydrolyzation diffusion method with wheat uptake N were raised obviously, and all reached 5% or 1% significant level. Of which, the NH + 4-N mineralized by one week waterlogging and NO - 3-N leached by two weeks formal aerobic incubation, as well as NH + 4-N extracted by Conway method varied greatly. The correlation coefficients between mineralizable N and uptake N of wheat above ground raised from 0.443, 0.119, 0.259 to 0.866, 0.767, 0.763, respectively. It showed that the poor effects of mineralizable N on reflecting soil N capacity were influenced and disturbed by initial NO - 3-N, warning researcher to pay more attention to correctly evaluate the function of mineralizable N when soil initial NO - 3-N is higher .