Nutrient cycling in a poplar plantation (Populus trichocarpa x Populus deltoides 'Beaupre') on former agricultural land in northern Belgium

Hydrological fluxes, atmospheric deposition, litterfall, and soil percolation of the most important nutrients were measured in an 18-year-old poplar plantation on a well-drained silt loam soil during 2 consecutive years. Downward soil water flux and transpiration are the most important factors in the water balance. Around 80% of total nitrogen input (6.6 and 6.5 kmol center dot ha(-1) in years 1 and 2, respectively) originates from litterfall. After nitrification only a negligible amount of nitrate leaches during the growing season. Yearly uptake of nitrogen by the poplar ecosystem (woody biomass, leaves, and ground vegetation) approximately equals the input, of which more than 50% is accounted for by the leaves. This indicates very efficient nitrogen cycling. Total deposition of base cations originates from two processes, dry deposition (Mg2+ and Ca2+) and canopy leaching (K+ and Ca2+). Litter input of Ca2+ represents about 83% of the total input (stand deposition + litterfall), Mg2+ about 61%, and K+ less then 50%. Percolation of base cations at 1 m depth is very limited. Rather high Ca2+ and K+ contents of the woody biomass can lead to high exports at harvest. Nutrient cycling in the poplar stand proved to be very efficient, with no significant nutrient losses.