Summary Band 25

Geißen, V., Schöning, A. & Brümmer, G. W. (1999): A redevelopment concept for strongly acidic forest soils - an example for the Kottenforst near Bonn.

 

We investigated the influence of liming and P,K fertilization on soil chemical parameters, microflora and soil fauna as well as on leaf litter decomposition rates in deciduous and spruce forest soils. Furthermore, we tried to establish artificially endogeic and anecic species of lumbricides in the forest soils.

The study was carried out from 1993 to 1997 on stagnic alisols on loess in the Kottenforst near Bonn. We conducted a field experiment with six plots each in an oak-beech and a spruce forest. In 1988, 1994 and 1995 we added different amounts of dolomite, partly combined with P,K fertilization (0 (control), 3t/ha Dolomit, 3+3 t/ha, 3+6 t/ha + P,K, 3+6+6 t/ha + P,K). In autumn 1994, we tried to colonise endogeic and anecic species of lumbricides in the plots.

Liming led to decreasing contents of mobile heavy metals and mobile aluminium as well as increasing pH values and higher contents of Ca and Mg in the organic layers and the Ah horizon. These changes were more obvious in the deciduous forest than in the spruce forest. The highest application of dolomite (3+6+6 t/ha + P,K) produced the most distinct changes.

The biomass of microflora and earthworms increased after the treatment, taking a similar development. The content of mobile nutrients showed positive correlations with the biomass of both microflora and earthworms in the plots treated, whereas mobile heavy metals and aluminium showed negative relationships. The goodness of fit between soil chemical parameters and the biomass of microflora and earthworms was dependent on the initial supply with nutrients and potentially harmful substances.

Only endogeic but no anecic species of lumbricides could be established in the limed plots. Endogeic species caused an increasing earthworm population after the treatment, especially in the deciduous forest soils.

In the deciduous forest, the abundances of collembola were significantly higher in the control plot than in the plots treated whereas the diversity was significantly lower. In the spruce forest, this phenomenon was not found. In both forest types, the reactions of some collembolan species to changing soil chemical parameters were described.

Litter decomposition rates were higher in the spruce than in the decidous forest due to a closer C/N ratio of the spruce needles. In our investigation, the impact of the macro- and mesofauna on the process of decomposition in forests soils was small, compared to the influence of the microorganisms. In the decidous forest, the decomposition rates were at a maximum in the plot treated with 3+3 t/ha dolomite. In the spruce forest, the plots treated with 3+6 t and 3+6+6 t dolomite per ha had the highest decomposition rates.

Liming and fertilization led to an increased supply of mobile nutrients and a decrease of mobile aluminium and heavy metals as well as a balanced ratio between macro- and micronutrients. Consequently, the initially found mesofauna-microflora communities changed into macrofauna-mesofauna communities with an increased biological activity. This phenomenon was especially found in the deciduous forest.

The amount of lime and fertilizer needed to improve forest soils cannot be generalized. It should be calculated in relation to the individual location and its chemical status.

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