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

In a homogeneous Corsican pine (Pinus nigra ssp laricio) stand, situated in a region of intensive livestock breeding, effects of different NHx 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 NH4+. 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 (0–10 cm) were taken and analysed on pH---H2O 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−1 year−1), where up to twice as much NH4+---N was found as in the monitoring plot. A forest edge zone of 180 m with significantly higher NH4+ deposition could clearly be delineated. Serious indications were found that all NH4+ was nitrified but that this process was slowed down. The variation in NH4+ depositions was clearly reflected in the state of soil acidification: pH---H2O and pH---KCl values varied between 3.1 (edge) and 3.8 (centre), and 2.4 (edge) and 2.8 (centre) respectively.