Biogenic nitric oxide emissions from cropland soils

Emissions of nitric oxide (NO) were determined during late spring and summer 1995 and the spring of 1996 from four agricultural soils on which four different crops were grown. These agricultural soils were located at four different sites throughout North Carolina. Emission rates were calculated using a dynamic flow-through chamber system coupled to a mobile laboratory for in-situ analysis. Average NO fluxes during late spring 1995 were: 50.9±47.7 ng N m−2 s−1 from soil planted with corn in the lower coastal plain. Average NO fluxes during summer 1995 were: 6.4±4.6 and 20.2±19.0 ng N m−2 s−1, respectively, from soils planted with corn and soybean in the coastal region; 4.2±1.7 ng N m−2 s−1 from soils planted with tobacco in the piedmont region; and 8.5±4.9 ng N m−2 s−1 from soils planted with corn in the upper piedmont region. Average NO fluxes for spring 1996 were: 66.7±60.7 ng N m−2 s−1 from soils planted with wheat in the lower coastal plain; 9.5±2.9 ng N m−2 s−1 from soils planted with wheat in the coastal plain; 2.7±3.4 ng N m−2 s−1 from soils planted with wheat in the piedmont region; and 56.1±53.7 ng N m−2 s−1 from soils planted with corn in the upper piedmont region. An apparent increase in NO flux with soil temperature was present at all of the locations. The composite data from all the research sites revealed a general positive trend of increasing NO flux with soil water content. In general, increases in total extractable nitrogen (TEN) appeared to be related to increased NO emissions within each site, however a consistent trend was not evident across all sites.