Ammonia volatilization from urea in alfalfa field with different nitrogen application rates, methods and timing

Ammonia (NH3) volatilization from agricultural activities contributes to climate change and nitrogen (N) loss. Nitrogen management method has an important effect on NH3 volatilization. The purpose of this study was to evaluate the influence of N application rate, method and timing on NH3 loss from alfalfa field. In 2017 and 2018, NH3 volatilization was measured by the calibrated Drager-Tube method under banding, surface broadcasting and center-pivot fertigation methods with three N application rates (27.6, 48.3, 69.0 kg N ha(-1) for each alfalfa cutting). Different application timing (7:00, 12:00, 17:00) was applied for sprinkler fertigation in 2017. The results showed that with irrigation method of center pivot, the two-year averaged cumulative NH3 loss under sprinkler fertigation was 6.80 kg N ha(-1), was similar to that under broadcasting and 32.55 % higher than that under banding. With the increase of N application rates, the cumulative NH3 loss increased but NH3 loss rate decreased. For different treatments, NH3 loss rate ranged from 1.76 % to 3.88 %. Cumulative NH3 loss for a growing season was only 5.00 kg N ha(-1) for sprinkler fertigation at dusk, which could be significantly reduced by 20.38 % and 23.31 % compared with those in the morning and at noon, and even lower than that under banding. Meanwhile, instantaneous NH3 loss flux had a significantly positive correlation with temperature in the two years. Based on our results, in order to minimize NH3 loss, sprinkler fertigation at dusk was more recommendable to the urea application for alfalfa in the North China.