Ammonia Exchange from Soils-Laboratory Study.

The exchange of ammonia between terrestrial ecosystems (soil, litter, plant surfaces, and through plant stomata) and the atmosphere is bidirectional. Quantifying ammonia exchange over agricultural ecosystems is necessary to improve our understanding of the fate and transport of ammonia in the environment. The bidirectional exchange of ammonia with environmental surfaces is controlled by the compensation point. This is especially true for bi-directional ammonia exchange over crops following N fertilizer application. This work focuses on the exchange of ammonia with soil surfaces. In particular, one objective is to assess/develop a soil extraction procedure that will better predict whether a soil will absorb or emit ammonia from the atmosphere. Past experience using traditional extraction protocols (e.g. 2M KCl) suggests that the amount of extractable ammonium removed from soils overestimates the fraction of soil ammonium that is available for soil-atmosphere exchange of ammonia. It has been proposed that part of the reason for this apparent over-estimate might be liberation of ammonium from microbial cells that are destroyed during the concentrated salt extraction, and/or displacement of ammonium from the soil complex that would kinetically not be involved with the ammonia equilibrium. Critical soil parameters that need to be considered include soil pH, soil texture, cation exchange capacity, soil moisture, and soil organic matter content. Time integrated measurements of ammonia emissions from treated soils are made under controlled conditions using annular denuder technology. “Success” is defined as being able to characterize the air/soil interface sufficiently well in order to accurately predict the soil ammonia compensation point and better model emissions or deposition of ammonia from soils.