A CUVETTE DESIGN FOR FIELD AND LABORATORY MEASUREMENT OF WATER AND AMMONIA FLUX FROM SOILS IN A SHORT GRASS PRAIRIE

Development of micro-meteorological methods has made it possible to es timate ammonia (NH3) volatilization in the field. However, this method requires field size plots which are not possible to use under many ci rcumstances such as evaluation of volatile loss of NH3 from wine patch es. Cuvettes are the only alternative available for direct estimation of NH3 flux from small sites. This work describes the use of evaporati on of water from a freely evaporating surface as a method of developin g a cuvette which can provide realistic estimates of NH3 volatilizatio n in the field. Nitrogen-15 labeled urea solutions were used to evalua te the overall performance of the cuvette system. A number of design c onsiderations are discussed. Using evaporation rates was found to be a satisfactory method to determine operating parameters of a cuvette in the field. Nighttime and daytime conditions varied in such a way that it was necessary to use difference conditions for each. It was necess ary for daytime conditions to mix the air inside the cuvette. Recovery of labeled N averaged 70.7% in capped micro-plots and 71.8% in uncapp ed micro-plots. The cuvette system appeared to provide realistic estim ates of NH3 volatilization in the field.