Soil ammonia (NH₃) emissions are often overlooked pathways for ecosystem N loss; however, they may help sustain ecosystem nitrogen (N) limitation, especially in arid regions where hydrologic N losses are relatively small. To characterize controls over NH₃ emissions, we measured NH3 losses from six dryland sites along a gradient in soil pH, atmospheric N deposition, and rainfall. We also added ammonium (NH₄⁺) to determine whether emissions were limited by N. Soil NH3 emissions were positively correlated with pH (R² = 0.90, p = 0.002), reaching 24.2 ± 16.0 µg N-NH₃ m^-2 hr^-1 at the most alkaline site. Wetting soils with NH₄⁺ solutions increased NH3 emissions from alkaline and moderately acidic soils (F_1,35 = 14.7, p < 0.001), suggesting that N can stimulate NH₃ volatilization regardless of pH. These results suggest that both pH and N act as proximate controls over NH₃ losses and that these losses can reduce soil N accumulation.

Please see methods in the associated manuscript.

These data represent soil ammoina emission from six dryland sites in Southern California. Empty cells indicate that data are missing for a given observation.