PARENT SESSION
Oral Session #21: Nutrient cycling: Nitrogen.
Presiding: S. Hart
Monday, August 5. 1:00 PM to 3:45 PM. Grand Ballroom Central, Radisson.
Spatial variability in nitrogen-saturated soils: interactions of cation mobility and substrate quality with N dynamics.
GILLIAM, FRANK*,1, LYTTLE, NIKKI1, THOMAS, ASHLEY1, ADAMS, MARY BETH2, 1 MARSHALL UNIVERSITY, HUNTINGTON, WV2 USDA FOREST SERVICE, PARSONS, WV
ABSTRACT- Several watersheds of the Fernow Experimental Forest (FEF), West Virginia, exhibit evidence of nitrogen (N) saturation, with a high degree of spatial variability in soil N processing. We addressed three questions regarding spatial variability: (1) What is the effect of soil nitrate production on soil cation mobility? (2) How does this effect vary spatially? (3) How does substrate quality affect net N mineralization and nitrification? To address the first two questions we collected soils with extreme high versus low rates of N processing within each of two watersheds, WS3 (treated with ammonium sulfate) and WS4 (untreated control). Samples of mineral soil were analyzed for extractable (available) ammonium, nitrate, calcium, and aluminum before and after 28-d incubations at 10, 20, and 30 C. To address the third question, we decreased C/N ratios in the untreated/low N soil (exhibiting low net N mineralization and no net nitrification) by adding glycine, and increased C/N ratios in the untreated/high N soil (exhibiting high net N mineralization, essentially 100% as nitrification) by adding sucrose. Mobility of calcium and aluminum generally increased with mobility of nitrate in all soils except the untreated/low N soil. Additions of glycine greatly stimulated net N mineralization in this soil, but failed to initiate net nitrification. Additions of sucrose resulted in net immobilization of ammonium and nitrate in untreated/high N soil. Results suggest that increased nitrification enhances calcium leaching and aluminum toxicity in N-saturated soils, and that substrate quality is not necessarily a good predictor of soil N processing.
KEY WORDS: nitrogen saturation, cation leaching, aluminum toxicity, C/N ratio