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

Ammonia (NH3) volatilization is one of the main pathways of N loss from agricultural cropping systems. This study evaluated the NH3–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−1to irrigated, strip‐till corn production systems for 2 yr using semi‐static chambers (semi‐open and open) to measure NH3–N loss. The efficiency of the semi‐static chambers in estimating NH3–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 NH3–N recoveries and calibration factors. Immediate irrigation with 16 to 19 mm of water 1 d after N fertilization probably limited NH3–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 NH3–N loss when compared to the other N sources. Analyzed across years, estimated NH3–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 NH3–N volatilization from polymer‐coated urea N sources such as ESN. The open‐chamber method was a viable, low cost method for estimating NH3–N loss from small field plot N studies.