Impacts Of Fertilizer Management Practices On Soil Greenhouse Gas Fluxes From Managed Forest Ecosystems Of The Pacific Northwest US.

Nitrogen fertilizer is applied over a range of soil and stand types throughout the Pacific Northwest. However, the impacts of N-fertilizer management practices on greenhouse gas (GHG) emissions have not been well studied. Understanding the impacts of N-fertilization on GHG fluxes is an essential first step to mitigating climate change effects. Therefore, studies were established in managed forest ecosystems in the spring of 2012 on soils derived from sedimentary and volcanic parent materials.  Additionally, two stand ages, young (20 years) and old (35 years), were selected within each soil group.  The treatments in each stand age included control (no fertilizer), urea [at two application rates; normal (224 kg N ha^-1) and high rate (448 kg N ha^-1)], and coated urea fertilizer (CUF) with volatility control (224 kg N ha^-1). Fertilizers were applied in the spring and fall. Vented static chambers were installed and used for gas sampling. The treatments were laid out in a randomized complete block design with four replications. Sampling continued every three months for one year. Soil air samples were analyzed for CO₂, N₂O, and CH₄. Soil moisture and temperature were also collected at 10cm depth simultaneously with gas sampling. The average CO₂ fluxes for control, coated urea, urea at normal rate and high rate plots were 1.87, 2.18, 2.32 and 2.49 g m^-2 d^-1, respectively. Similarly, N₂O fluxes were 0.08, 0.15, 0.20 and 0.77 mg m^-2 d^-1 and CH₄ uptake were 1.10, 0.96, 0.97 0.90 mg m^-2 d^-1 for control, CUF, urea at normal rate and high rate, respectively. Young stand age emitted 21% more CO₂, 194% more N₂O and reduced CH₄ uptake by 18% compared to older plantations. Stands on sedimentary soils emitted 8% more CO₂ and reduced CH₄ uptake by 15% than the soil derived from volcanic materials.