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SEASONAL VARIATIONS OF NITRIC OXIDE FLUX FROM AGRICULTURAL SOILS IN THE SOUTHEAST UNITED STATES
Citation:
Aneja, V., W. P. Robarge, L. Sullivan, T. Moore, T Pierce*, C D. Geron*, AND B. Gay*. SEASONAL VARIATIONS OF NITRIC OXIDE FLUX FROM AGRICULTURAL SOILS IN THE SOUTHEAST UNITED STATES. TELLUS 48B:626-640, (1996).
Description:
Fluxes of nitric oxide (NO) were measured from the summer of 1994 to the spring of 1995 from an intensively managed agricultural soil using a dynamic flow through chamber technique in order to study the seasonal variability in the emissions of NO. The measurements were made on a Norfolk sandy loam (Fine-Loamy, Siliceous, Thermic Typic Paleudult) soil located at an agricultural research station in the Upper Coastal Plain region of North Carolina. Soil nitric oxide fluxes from 3 crops, representing 3 levels of fertilizer application (corn, 158 kg N ha-1; cotton, 68 kg N ha-1; and soybean, 0 kg N ha-1), were measured in each season (summer, fall, winter, and spring). Additional measured soil parameters included soil temperature, soil water content (expressed as percent water filled pore space, % WFPS), and extractable nitrogen. The greatest NO flux observed in each crop occurred during the summer (June to August) measurement period (corn, 21.9 +/- 18.6 ng N m-2 s-1; cotton, 4.3 +/- 3.7 ng N m-2 s-1; and soybean, 2.1 +/- 0.9 ng N m-2 s-1). NO flux decreased in each crop through the fall months to a minimum flux in the winter. Application of fertilizer during the spring months again produced substantial NO flux, but not as high as during the summer months. Over 80% of NO flux from the three crops measured occurred in the summer months with an estimated 5% of the nitrogen applied as fertilizer emitted as NO in a year's time. The corn crop, which had the highest amount of applied fertilizer, had the highest average yearly NO flux (7.0 +/- 4.8 ng N m-2 s-1) followed by cotton and soybean in order (1.7 +/- 1.2 ng N m-2 s-1 and 1.0 +/- 0.3 ng N m-2 s-1, respectively). NO flux from soil tracked soil temperature very closely throughout the year, especially through the summer and spring months. However, NO flux measured under a cotton canopy decreased when soil temperature was >25 degrees C and soil moisture content was <20% WFPS. Overall, the data support the assumption that in the United States, which has naturally emitted VOC's and large acreages of fertilized soils, NO emissions from agricultural soils may result in the formation of Tropospheric ozone, especially during the summer months when NO emissions are highest.