The nitrogen budget of a hybrid poplar plantation in Minnesota

Total aboveground tree biomass represented only 1.6% of the total N capital. Stable soil inorganic N was the largest pool, 5670 kg N.ha^-1, and constituted 93% of all N within the site. Labile soil inorganic N and microbial N represented 5.6 and 1.6% of stable soil organic N, respectively. Nitrogen mineralization averaged 56 kg N.ha^-1.yr^-1, and 66% of that production was oxidized to NO₃ ^-. Losses of N by denitrification and leaching were small compared with the magnitude of the other fluxes. A relatively high rate of plant uptake and production maintained NH₄ ⁺ and NO₃ ^- pools at low levels, minimizing N exports to the atmosphere and groundwater. -from Authors