Journal of Conference Abstracts

Effects of Experimentally Enhanced Chronic Nitrogen Deposition on Nutrient Dynamics in a Hardwood Forest

Robert Boutin (boutin@cfl.forestry.ca)

Natural Resources Canada, Canadian Forest Service, 1055 du P.E.P.S.,
P.O. Box 3800, Sainte-Foy, Québec, G1V 4C7, Canada.

Nitrogen saturation, soil acidification and altered N cycling in forested watersheds may be induced at lower rate of N deposition than previously believed. This brings the necessity to reevaluate the actual available figures for long-term critical N loads for forest ecosystems which vary between 2 and 20 kg ha^-1 yr^-1. In a previous experiment on deep soil frost effects, we have shown that the hardwood forest at the Duchesnay experimental station (50 km NW of Québec City, Canada) was prone to serious N, base cation and Al leaks when an enhancement of nitrification occurred following disturbance. In order to test if an enhanced chronic N deposition will contribute to an accelerated shift towards saturation state, we started to apply ammonium nitrate in 1995 at a rate of 25 kg ha^-1 yr^-1 on three 20 x 20 m plots; three similar plots were used as controls. After two years of application (50 kg ha^-1 which is equivalent approximately to the content of N in the annual leaf litterfall), soil solution monitoring showed only a slight leak of nitrate down the main rooting zone at the 30 cm depth. Incident deposition, throughfall, litterfall, surface soil and vegetation monitoring are also conducted. Results from the two years of treatment will be discussed.