Nitrogen transformations in the vadose zone of a small, zero-order Piedmont watershed in Watkinsville, Georgia
Muckler, James Frank
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Soil water samples were collected in a small, Piedmont watershed in nine suction-lysimeters at four depths in the vadose zone: 0.35, 0.5, 1.25, and 1.75 m, and analyzed for nitrate-N, ammonium, urea, total nitrogen, dissolved organic carbon (DOC), and ferrous and ferric iron concentrations. Soil water potential was inferred from pressure heads measured in tensiometers at 0.5, 1.0, and 1.5 m depths. Although nitrate-N concentrations were spatially variable and periodically high (20 – 64 mg/L) at 0.35 and 0.5 m depths, nitrate-N consistently decreased with depth to the deepest lysimeter at 1.75 m (0 – 6 mg/L), which was likely due to denitrification. Also, DOC decreased with depth. Other geochemical trends were not so clear in the limited data. Stable nitrogen isotope ratios in soils were compared to possible nitrogen sources that found manure-source signatures in shallow soils and chemical fertilizer-source signatures in deeper soils.