Soil acidification along an ammonium deposition gradient in a Corsican Pine stand in northern Belgium

In a homogeneous Corsican pine (pinz~ nigra ssp laricio) stand, situated in a region of intensive livestock breeding, effects of different NI-J doses on soil acidification were studied. Throughfall collectors were placed every 25 m on a transect of 1.4 km, oriented according to the dominant wind direction. The throughfall water was analysed on NH,+. A permanent monitoring plot is situated in the middle of the transect where quantity and chemical composition of different water fractions are monitored fortnightly. Along the transect, soil samples of the upper mineral soil (O-10 cm) were taken and analysed on pH-H,O and pH-KCl. The measured deposition of NH4+-N was very high, especially in the forest edge at the prevailing wind direction (55 kg ha-’ year-‘), where up to twice as much NH,+-N was found as in the monitoring plot. A forest edge zone of 180 m with significantly higher NH,+ deposition could clearly be delineated. Serious indications were found that all NH,+ was nitrified but that this process was slowed down. The variation in NH,+ depositions was clearly reflected in the state of soil acidification: pH-H,O and pH-KC1 values varied between 3.1 (edge) and 3.8 (centre), and 2.4 (edge) and 2.8 (centre) respectively.