Nitrogen Source Effects on Ammonia Volatilization as Measured with Semi‐Static Chambers

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 15 N 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.