Update 2012: N-Source Comparison

Objectives

Daniel Schellengerg, Ph.D. student, at the orchard sampling site in Kern County.

To compare N2O emissions from two different forms of nitrogen (N) fertilizer: urea ammonium nitrate and calcium ammonium nitrate.
To evaluate temporal variability of N2O emissions with respect to environmental factors such as water-filled pore space and temperature.
To determine temporal dynamics of N2O emissions with respect to soil inorganic N pools during a soil drying period.

Summary of the Experiment

Nitrous oxide emissions after three fertigation events in 2009 showed distinct differences which have been consistent throughout the entire period of emissions monitoring:

In April of 2009, N2O-N emissions increased and peaked at about 2.5 umol m-2 hr-1 following application of a CAN solution at 17% N (CAN17); it was slightly higher at 3.4 umol m-2 hr-1 following application of a UAN solution at 32% (UAN32).
In June 2009, N2O emissions increased to 5.4 umol m-2 hr-1 following fertigation with CAN17 while it was significantly higher at 14.3 umol m-2 hr-1 for UAN32.
Finally, in October 2009 peak N2O emissions were 2.2 umol m-2 hr-1 for CAN17 while it was 4.8 umol m-2 hr-1 for UAN32. These differences were generally statistically significant. In June, 2011, N2O emissions measurements were taken at predawn (5:00 a.m.) and in late afternoon (2:00 to 4:00 p.m.) to capture fluxes at the observed period of lowest and highest emissions, respectively, to capture the amplitude of diurnal variation.

Results

Our results indicated significant diurnal variation and this is being incorporated into the annual budget calculations. Frequent N2O emissions monitoring following the N fertilizer applications revealed durations of from 36 up to 100 hours (Fig. 1). At the present time, we don’t have a good explanation for the observed variation, but it is apparent that it is not soil temperature and moisture content alone and will complicate DNDC modeling efforts. (Daniel Schellenberg et al. 2012).

Fig. 1 (right). Nitrous oxide emissions after application of 60 lb per acre in April and June and 40 lb per acre in October UAN and CAN. Arrows indicate timing of N fertilizer application in Lost Hills, CA 2009 and 2010.

For more information see the presentations and publications under Outreach