EMISSIONS OF NO FROM SOIL AT A RURAL SITE IN CENTRAL TENNESSEE

Field measurements of soil emissions of NO from a Mountview silt loam soil with three land uses (forest, fertilized pasture, and fertilized corn) were made on a commercial farm during a summer and autumn sampli ng period. A new automated closed-chamber sampling system was develope d to allow simultaneous measurements on five chambers per 100 m2 plot. Individual chambers with hinged tops, covering 0.3 m2 of soil area we re pneumatically operated via data logger control to sample soil NO fl ux every third hour. Spatial variability in emission rates was high. F or each land use type the range from the lowest to the highest emittin g chamber was approximately threefold. Land use type significant affec ted soil NO emissions. The fertilized pasture had the highest mean emi ssion rate (44.1 ng N m-2 s-1), followed by the fertilized com (27.0 n g N m-2 s-1), and the forest (8.4 ng N m-2 s-1). NO emission rates and soil nitrate levels at the forest plot were considerably higher than at other forest sites in the region, possibly due to runoff from an ad jacent fertilized hayfield. The results of this study, when extrapolat ed to a regional estimate, suggest that emissions of NO from soils cou ld play a significant role in summertime tropospheric ozone photochemi stry in the southeastern United States.