The Illinois Soil Nitrogen Test (ISNT) has showed promise as a tool to predict if N fertilizer is necessary for corn production by estimating potentially available soil N. However, the reported method for measuring ISNT values can be affected by temperature gradients across the bench griddle. Furthermore, this method requires a relatively large amount of bench space, and rotation of the jars on the griddle is time consuming. The Conway Diffusion Unit (CDU) is commonly used in some Asian countries for estimating soil available N. The CDU and the recommended method for the ISNT were compared using soils varying in OM contents and management history. Our results indicate that the two methods measure the same forms of soil N and are not significantly different from one another. Use of the CDU would allow more accurate and uniform temperature control and save space and labor.