Efficient use of nitrogen (N) fertilizer is important to achieve optimum crop yields while avoiding potential contamination of surface and ground water. A major obstacle in achieving optimum N fertilization is the difficulty of predicting soil organic N mineralization under field conditions. Since soils differ in their N‐supplying capacity, there is need for a testing procedure that will enable producers to make an accurate assessment of soil N availability. The purpose of this study was to evaluate electro‐ultrafiltration (EUF) and autoclave techniques to estimate soil N mineralization relative to N uptake by corn from unfertilized plots. Five different geographical locations in Nebraska were selected to encompass climatic conditions and soil types typically encountered throughout the state. Soil organic N mineralized determined by plant N uptake varied between geographical locations and ranged from 13 to 131 kg ha‐1. Data from both laboratory procedures were poorly correlated with crop N uptake across geographic locations. However, multiple regression including potentially mineralizable N (PMN), residual soil N, and growing degree days as independent variables resulted in a high correlation (R2≥ 0.93) with total N uptake. The results indicated that mineralization of organic matter (OM) can represent an important source of N and that it may be feasible to quantify soil organic matter mineralization by laboratory testing procedures for a broad range of climatic conditions.