Corn does not respond to N fertilizer on fields that have a high concentration of amino sugar-N. The Amino Sugar-N test can classify fields into two categories, that sites have a high probability of needing N fertilizes and those that are not likely to need fertilizer. Application of N fertilizer to maize fields during the growing season should reduce the amount of N lost to the environment and improve the efficiency of N use in maize production. the objective of this study was to calculate a critical concentration of amino sugar N for silage corn under Connecticut conditions. Twenty-four experiments were conducted , ten of the experiments were part of the trials established for measuring the effect of delaying N on the yield of silage corn, and 14 (trials) were on farmers’ fields throughout Connecticut from 2001 to 2004. The trials on farmers' fields consisted two treatments, a zero N rate and a high N rate, and either three or four replications. soil samples were collected, using 2 depths 0-15 and 0-30 cm, from each replication in early spring, and from the zero N plots at PSNT time. The Relative Yield (RY) of corn was calculated by divide the yield for the no N  treatments by the yield for the high N treatment or treatments or the average yield for the site if there is no response to N at site.