FIELD COMPARISON OF STATIC AND FLOW-THROUGH CHAMBER TECHNIQUES FOR MEASUREMENT OF SOIL NO EMISSION

A field comparison of flow-through and static chamber techniques for m easuring soil emissions of NO was performed on fertilized soil at a co mmercial cotton (Gossypium hirsutum L.) farm near Muscle Shoals, Alaba ma, during July 1992. The purpose of the study was to compare soil NOx emissions data taken using two different techniques at a common field site. Emission rates with collocated chambers using the two technique s were compared, and spatial means were also compared for 17 National Oceanic and Atmospheric Administration (NOAA) plots and 10 Tennessee V alley Authority (TVA) plots. Emission rates of NO at the site covered a broad spectrum, ranging from less than 1 to greater than 100 ng N m( -2) s(-1). Data from collocated TVA static and NOAA flow-through chamb ers showed a correlation coefficient of 0.98 with a linear regression slope of 0.97. A t test indicated that the mean difference was not sta tistically different than zero. The plot mean emission rates were 17.7 and 18.0 ng N m(-2) s(-1) for the TVA and NOAA chambers, respectively , for an 8-day comparison period. These findings indicate that data se ts collected with these methods are comparable and may be combined wit hout concern for differences in technique. These results also reveal t hat the techniques used by each group in attempting to characterize ov erall site mean emissions are remarkably similar, despite differences in chamber size, plot location, extent of areal coverage, and random e rror associated with the measurements. This finding is significant in that it means that field data used to characterize emissions estimates by both protocols can be pooled to better estimate regional soil NO e mission inventories.