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 livest ock production, comparable stands of Corsican pine and silver birch were st udied for (1) NH4+ and NO3- concentrations in throughfall water and soil so lution and (2) depositions and leaching of NH4+ and NO3- to groundwater. In each stand, throughfall collectors and porous cup lysimeters at three dept hs (0.1 m, 0.5m and im) were installed in three replicated sets. Throughfal l concentrations of ammonium and nitrate were significantly different for b oth species as well as soil solution concentrations of nitrate at all depth s. Under pine, nitrate concentrations of the soil solution at Im depth clea rly exceeded the Belgian critical level for drinking water (50 mg.l(-1)). U nder birch, this level was only sporadically exceeded. During the sampling period, the depositions of NH4+-N and NO3--N reached respectively 21.6 kg/h a and 6.3 kg/ha under birch and 81.3 and 15.2 kg/ha under Corsican pine. Ni trate-N leaching under silver birch amounted 25.4 kg/ha whereas 56.4 kg/ha was measured under Corsican pine.