Characterization of biogenic nitric oxide source strength in the southeast United States

Emissions of nitric oxide (NO) were measured during the summer of 1995 from 4 crops, located at three different sites throughout North Carolina. These sites were chosen to represent major physiographic regions of the Southeast US, in an effort to compare fluxes from different agriculturally managed soils. Emission rates were determined using a dynamic flow-through chamber system. In order to understand the NO flux from the different soil and crop types, measurements were made on corn and soybean crops in the coastal region, tobacco in the Piedmont region, and corn in the upper Piedmont region of North Carolina. Average NO fluxes were 5.5 f 2.2 ng N me2 s-‘, 20.7 + 19.2 ng N me2 s-‘, 4.1 + 1.4 ng N m-2s-1, and 8.5 2 4.9 ng N me2 s-l respectively for corn and soybean in the coastal region, tobacco in the Piedmont region, and corn in the upper Piedmont region. We were only able to detect an exponential dependence of NO flux on soil temperature at two of the locations. Tbe composite data of all the research sites revealed a general trend of increasing NO flux with soil water content or increasing extractable nitrogen in the soil, however, the day to day variations within each site did not reveal the same trends. We feel that acquisition of a soil NO flux data set in this fashion, which consists of observations collected over different points in both space and time, makes attempts to model soil NO flux in terms of different soil parameters difficult.