Comparison of nitrate leaching under Silver birch (Betula pendula) and Corsican pine (Pinus nigra ssp laricio) in Flanders (Belgium)

In a forest in Flanders (Belgium), situated in a region of intensive livestock production, comparable stands of Corsican pine and silver birch were studied for (1) NH4+ and NO3- concentrations in throughfall water and soil solution and (2) depositions and leaching of NH4+ and NO3- to groundwater. In each stand, throughfall collectors and porous cup lysimeters at three depths (0.1 m, 0.5m and im) were installed in three replicated sets. Throughfall concentrations of ammonium and nitrate were significantly different for both species as well as soil solution concentrations of nitrate at all depths. Under pine, nitrate concentrations of the soil solution at Im depth clearly exceeded the Belgian critical level for drinking water (50 mg.l(-1)). Under birch, this level was only sporadically exceeded. During the sampling period, the depositions of NH4+-N and NO3--N reached respectively 21.6 kg/ha and 6.3 kg/ha under birch and 81.3 and 15.2 kg/ha under Corsican pine. Nitrate-N leaching under silver birch amounted 25.4 kg/ha whereas 56.4 kg/ha was measured under Corsican pine.