Ammonia (NH 3) volatilization is one of the main pathways of N loss from agricultural cropping systems. This study evaluated the NH 3-N loss from four urea-based N sources (urea, urea-ammonium nitrate [UAN], SuperU, and ESN [polymer-coated urea]) surface band applied at a rate of 200 kg N ha -1 to irrigated, strip-till corn production systems for 2 yr using semi-static chambers (semi-open and open) to measure NH 3-N loss. The efficiency of the semi-static chambers in estimating NH 3-N loss under field conditions was determined using 15N labeled urea applied at rates of 50, 100, and 200 kg N ha -1. Both chamber types had similar NH 3-N recoveries and calibration factors. Immediate irrigation with 16 to 19 mm of water 1 d after N fertilization probably limited NH 3-N volatilization from surface-applied N fertilizers to a range of 0.1 to 4.0% of total N applied. SuperU, which contains a urease inhibitor, had the lowest level of NH 3-N loss when compared to the other N sources. Analyzed across years, estimated NH 3-N losses for the N sources were in the order: ESN=UAN > urea > SuperU. Both years the results showed that measurement time may need to be increased to evaluate NH 3-N volatilization from polymer-coated urea N sources such as ESN. The open-chamber method was a viable, low cost method for estimating NH 3-N loss from small field plot N studies.
