An important improvement in estimating economic N applications for com production would be to predict the soil N supply capacity each year. The objective of this research is to evaluate the adaptability and potential calibration of the amino sugar-N based Illinois N Soil Test in corn production fields across diverse Iowa soils. Nitrogen rate trials were conducted at multiple sites over several years. many on producer fields. Soil samples were collected at 0-6 and 0-12 inch depths in the fall and spring preplant where no N was applied. Samples were analyzed for hydrolyzable amino sugar-N (limited nwnber of sites). the Illinois N Soil Test, soil organic matter, and total soil N. Com response to fertilizer N was determined through change in grain yield. The hydrolyzable amino sugar-N values correctly identified six of eight site-years as being N responsive or non-responsive. Two sites had high test values, but were responsive to applied N. The Illinois N Soil Test values for each sample depth and sample timing were not related to com yield response to applied N, and could not be calibrated on the soils studied. Also. the test did not differentiate between responsive and non-responsive sites. It is possible that .the amino sugar-N fraction measured by soil hydrolysis is a better predictor of N responsiveness than the Illinois N Soil Test but that needs to be confirmed by analysis of soil from additional sites. The Illinois N Soil Test values were similar for each sampling time. The Illinois N Soil Test did show a strong relationship with soil organic matter and total soil N. This indicates the test is reflecting multiple organic N pools or overall soil N rather than the specific amino sugar organic N fraction. Based on these results. the Illinois N Soil Test is not recommended for adjusting N applications to com on Iowa soils.