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United States Department of Agriculture

Agricultural Research Service

Title: Field-Scale Mapping of Ground Water Nitrate-N Distributions and Denitrification Potential Estimates for An Agroforestry Site in the Ozark Highlands, Usa

item DE Fauw, Sherri - UNIV OF ARKANSAS
item Sauer, Thomas
item Brye, Kristofer - UNIV OF ARKANSAS
item Savin, Mary - UNIV OF ARKANSAS
item Hays, Phillip - USGS
item Brahana, John - UNIV OF ARKANSAS

Submitted to: North American Agroforestry Conference
Publication Type: Abstract Only
Publication Acceptance Date: June 15, 2005
Publication Date: July 15, 2005
Citation: Defauw, S.L., Sauer, T.J., Brye, K.R., Savin, M.K., Hays, P.D., Brahana, J.V. 2005. Field-scale mapping of ground water Nitrate-N distributions and denitrification potential estimates for an agroforestry site in the Ozark Highlands [abstract]. North American Agroforestry. p. 25-26.

Technical Abstract: Nutrient assimilation, which occurs by some combination of plant up-take and a site's inherently patchy biogeochemistries, is ultimately controlled by catchment hydrodynamics. Biogeochemical processing of nitrate-N (nitrogen) in upland watersheds is very poorly known, and denitrification potential estimates for the thin soil veneers of the Ozark Highlands have yet to be documented. Since March 2001, nitrate-N distributions have been monitored from an array of 53 piezometers (0.5-5.6m deep) emplaced in a 4.3ha experimental agroforestry field (receiving split-field treatment of poultry litter to the eastern half in Spring, and a comparable annual N-load from commercial fertilizer applied on the western half in Spring and Fall). GIS-integrated mapping provides pivotal insights on seasonal variations in nitrate-N residing proximate to the subsoil-epikarst interface. In March 2001, the field contained several 'hot spots' with nitrate-N varying from 25.0-64.5mg/L. These patches most likely represented old loafing or feeding areas shedding nitrate-N in response to changes in subsoil pH, the delayed result of liming. Late winter peaks in ground water nitrate-N from this 5-year-old agroecosystem have steadied over the last two years (13.2mg/L for Mar2003; 12.0mg/L for Feb2004). Saturated hydraulic conductivities for three down-gradient wells (2.0-3.6m) in Johnsburg series soils range from 0.4-1.2mm/day. These baseflow values coupled with waxing and waning nitrate-N concentrations detected over the last three years suggest that denitrification (rather than leaching) prevails in one of the most hydrologically active portions of this field. Mean denitrification potentials vary from 7.11-20.80kg/ha/y; cross-validation is in progress using fluctuations in DOC and nitrate-N from the well array.

Last Modified: 4/18/2015
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