Slow release N fertilizers have potential to improve yield and nitrogen use efficiency (NUE) in winter wheat (Triticum aestivum L.) and maize (Zea mays L.). A slow release urea formaldehyde polymer (UFP) was compared with aqueous urea ammonium nitrate (UAN) [(NH2)2CO, NH4NO3] during a 2-yr field experiment in North Carolina. Crops were grown on Candor (sandy, siliceous, thermic Grossarenic Kandiudults), Portsmouth (fine-loamy over sandy or sandy-skeletal, mixed, semiactive, thermic Typic Umbraquults), and Cape Fear (fine, mixed, semiactive, thermic Typic Umbraquults) soils. Treatments were N source (UFP and UAN) and N rate (0, 50, 78, 106, 134, 162, and 190 kg N ha−1 for wheat and 0, 39, 78, 118, 157, 196, and 235 kg N ha−1 for maize). Both sources were band applied as a split application for wheat, whereas maize received UFP at planting and split application of UAN, which is the current standard practice. Based on years of research, NC producers' apply less than one-third of UAN at planting, with the remainder applied before the end of tillering (wheat) or at V4–6 (corn). For both crops and both sites, grain yield and NUE with UAN were statistically similar to or better than UFP. Laboratory incubations suggested UFP release of urea and urea hydrolysis were complete in less than 2 wk. Hence, UFP release was limited to a time scale of days, considered insignificant for summer crop (corn) growth conditions. Since the UFP did not significantly improve yield, UFP may only be economical if priced similar to UAN.