Precision Fall Urea Fertilizer Applications: Timing Impact on Carbon Dioxide, Ammonia Volatilization and Nitrous Oxide Emissions
To minimize ammonia (NH3) volatilization and nitrous oxide (N2O) emissions from fall applied fertilizer, it is generally recommended to not apply the fertilizer until the soil temperature decreases below 10 C. However, this recommendation is not based on detailed measurements of NH3and N2O emissions. The objective of this study was to determine the influence of fertilizer application timing on nitrous oxide, carbon dioxide, and ammonia volatilization emissions. Nitrogen fertilizer was applied at two rates (0 and 224 kg urea-N ha-1) to two soil moisture treatments (natural rainfall and natural + supplemental water) in mid-September, mid-October, and the beginning of November. Soil temperatures at fertilizer application were approximately 27 C, 16 C, and 5 C, in September, October, and November, respectively. Gas flux rates of N2O, CO2, and NH3were monitored every 4 hours for 3 weeks following application. As the season progressed from September to November, CO2and N2O emissions decreased. However, for ammonia, different results were observed and rates increased from September to October, however, emissions decreased thereafter. At the end of the November application, CO2, N2O, and NH3emissions were very low. These findings suggest that minimizing NH3and N2O losses requires a better understanding of the loss mechanisms.