Effect Of Fertilizer Management Practices On N2O Emissions From Managed Loblolly Pine Ecosystems.

Forest fertilization is a common silvicultural practice. Over one million acres are fertilized annually in the southeastern US; however, the effects of N-fertilization on N₂O emissions in managed forest ecosystems are poorly understood. Therefore, studies were established in loblolly pine (Pinus taeda L.) ecosystems in the Lower Coastal Plain of North Carolina during the summer of 2011. Three landscape positions: terrace (poorly drained), flat (moderately drained), and upland (well drained) were selected.  The treatments in each landscape position included control (no fertilizer), urea and coated urea fertilizer (CUF) with volatility control applied in the spring, summer, and fall seasons. The treatments were laid out in a randomized complete block design with four replications. Within each plot, vented static chambers were installed in both bed and interbed locations. Nitrogen-fertilizers were applied at 168 kg N ha^-1. Greenhouse gas (CO₂, N₂O, and CH₄) sampling started immediately after fertilizer application and continued every six weeks for about 18 months. Gas samples were analyzed for N₂O. Soil moisture and temperature were collected at 10cm depth simultaneously with gas sampling. Poorly drained soil had about 200% higher annual N₂O flux (1.39 kg ha^-1 yr^-1) compared to moderately and well-drained soils. Spring and summer fertilizer applications significantly reduced annual N₂O flux than that of fall. Urea applications significantly increased annual N₂O flux (1.14 kg ha^-1 yr^-1) compared to no-fertilizer control (0.22 kg ha^-1 yr^-1) but were similar with CUF (0.87 kg ha^-1 yr^-1). Fertilizer applied to forest planted on bed or interbed did not have any effects on N₂O fluxes.