Nitrous Oxide and Ammonia Fluxes in a Soybean Field Irrigated with Swine Effluent

In the United States, swine ( Sus scrofa ) operations produce more than 14 Tg of manure each year. About 30% of this manure is stored in anaerobic lagoons before application to land. While land application of manure supplies nutrients for crop production, it may lead to gaseous emissions of ammonia (NH 3 ) and nitrous oxide (N 2 O). Our objectives were to quantify gaseous fluxes of NH 3 and N 2 O from effluent applications under field conditions. Three applications of swine effluent were applied to soybean [ Glycine max (L.) Merr. ‘Brim’] and gaseous fluxes were determined from gas concentration profiles and the flux‐gradient gas transport technique. About 12% of ammonium (NH 4 –N) in the effluent was lost through drift or secondary volatilization of NH 3 during irrigation. An additional 23% was volatilized within 48 h of application. Under conditions of low windspeed and with the wind blowing from the lagoon to the field, atmospheric concentrations of NH 3 increased and the crop absorbed NH 3 at the rate of 1.2 kg NH 3 ha −1 d −1 , which was 22 to 33% of the NH 3 emitted from the lagoon during these periods. Nitrous oxide emissions were low before effluent applications (0.016 g N 2 O–N ha −1 d −1 ) and increased to 25 to 38 g N 2 O–N ha −1 d −1 after irrigation. Total N 2 O emissions during the measurement period were 4.1 kg N 2 O–N ha −1 , which was about 1.5% of total N applied. The large losses of NH 3 and N 2 O illustrate the difficulty of basing effluent irrigation schedules on N concentrations and that NH 3 emissions can significantly contribute to N enrichment of the environment.