Slow and controlled release fertilizers have often been used to prevent N loss through leaching. Recently, new slow release fertilizers have been developed and their potential use in corn production is an alternative to increase N efficiency. An incubation study was performed to measure and compare the release rates from two urea-formaldehyde (UF) liquid resins and conventional urea. Four different representative soils from corn production areas of Iowa were collected. The soils were classified as: Harps (Typic Calciaquoll), Nicollet (Aquic Hapludoll), Okoboji (Cumulic Hapluquoll) and Sac (Oxyaquic Hapludoll). Soil samples (10 g) were amended with solutions containing rates of N equivalent to 0, 50, 100, 150 and 200 kg N ha⁻¹ of urea and the UF materials and incubated at 20 ⁰C for 0, 7, 15, 30, 45 and 60 days. At the end of the respective incubation periods each sample was analyzed for nitrate-N (NO₃-N) and ammonium-N (NH₄-N). The results obtain showed that UF fertilizers might not meet the N requirements for corn production in Iowa due to the low percentage N recoveries (60 - 80% N) observed. The soils had different release rates mainly affected by pH and organic matter content. A two year trial was conducted to asses the effect of a polymer-coated urea (ESN) fertilizer upon corn biomass and grain N uptake and yield when applied in the fall or spring. Nitrogen fertilizer rates used for urea and ESN treatments were 0, 34, 67, 101, 135, 168 and 200 kg N/ha. The results obtained showed that corn biomass was not affected by the use of ESN or urea in particular. Biomass weight and N uptake tended to respond to N rates in some treatments. Grain yield always increased with N rate. However the effect of ESN and urea application varied from one year to the next and among locations.