Aluminiumformen in Pseudogleyen unter Laub- und Nadelwald

Forms of aluminium in pseudogley soils under deciduous and coniferous forests In pseudogleys under a near-natural oak-hornbeam forest and under three spruce stands of different age (5, 15 and about 70 years) several fractions of aluminium were extracted by a concentrated HCl/HNO₃-mixture, 0,2 M NH₄-oxalate/oxalic acid (pH 3,0), M NH₄Cl and water resp. The selected sites are situated close to each other and allow the assumption of an originally uniform state of the soils. The pH-values of the soils tend to be the lower the older the spruce stands are. The pH-values are correlated positively with acid soluble Al, negatively with oxalate soluble Al and NH₄Cl-exchangeable Al. The highest contents of water soluble Al were found in the soil of the oldest spruce stand. Compared with the soil under deciduous forest the acidification of the soils under spruce is connected with accelerated weathering of clay minerals, reduction of exchange capacity, displacement of exchangeable Ca by Al ions and finally with Al-toxicity. The high interception of acids by the spruce stands being situated at the lee side of the industrial district of Nordrhein-Westfalen, is discussed as a cause of the accelerated soil degradation.