On the northern winter range of Yellowstone National Park, Frank and Zhang measured ammonia volatilization at three times in 1995, at three topographic positions: hilltop, midslope, and slope-bottom. The amount of ammonia-N volatilized among the sites varied considerably, ranging from 0.6 g-N/m2 at Stevens Ck hilltop during April to 12.2 g-N/m2 at Blacktail hilltop during July. These values represent 1% and 24% of the urea-N added, respectively. ANOVA results indicated that ammonia loss was affected by landscape, topographic position, and season. Overall, the Blacktail sites averaged the highest rates of ammonia loss among the sites during the study, July rates tended to be highest, ammonia loss declined from hilltop to slope-bottom, except at Stevens Ck, and there was a particularly large efflux of ammonia from the Blacktail sites in July relative to earlier measurements. Ammonia loss was negatively correlated with CEC. CEC was a function of a combination of soil clay and carbon content. Plant biomass positively influenced CEC through its effect on soil C content. This study did not find soil pH to be associated with ammonia volatilization. These results indicate large spatial and temporal variation in ammonia loss from urine patches in Yellowstone Park grassland. Ammonia volatilization varied 24-fold among sites during the three sampling periods, indicating seasonal and topographic effects are important when considering landscape level rates of gaseous N loss.
Citations and enhanced abstracts for journals articles and documents focused on rangeland ecology and management. RSIS is a collaboration between Montana State University, University of Idaho, and University of Wyoming.