THE HUMUS OF A PARABRAUNERDE (ORTHIC-LUVISOL) UNDER FAGUS-SYLVATICA L AND QUERCUS-ROBUR L AND ITS MODIFICATION IN 25-YEARS

The humus of a loamy Orthic Luvisol containing a rich soil fauna formed on a boulder marl in the low-lying plain in the northwest of Germany near the Baltic sea under beech and oak with a mull humus was investigated in 1965 and 1986. Using a wet chemical procedure litter (proteins, polysaccharides, lignins) and humic components (fulvic and humic acids, humins) were separated. The results were combined with micro- and macromorphological observations and microbiotic and zootic investigations. The humus body has changed during the past 25 years. Decreasing bioturbation has induced a differentiation of the horizons in the organic layer, an accumulation of litter components and the development of an L- and an Oh-layer. The Of-layer has become tangled and laminated. The pH has decreased by half a unit. The translocation of fulvic acids has increased and the first signs of podzolization have been documented. The intensity of decomposition and humification has decreased during the past 25 years and therefore the humus form has changed from mull to moder. The main reason for this may be the decline of the earthworm population because of the lower pH and the deficiency of calcium as a consequence of the acid and proton input by air pollution.