Soil regenerative liming and its environmental effects

klaus von wilpert1, peter hartmann1, jürgen schäffer1
1 soil and environment, forest research institute freiburg

O 12.7 in Restoration and rehabilitation of ecosystems

17.07.2014, 15:50-16:10, H19

The main reason for forest decline in Central Europe was soil acidification caused by anthro­pogenic acid deposition. The amount of actual acid deposition recently dropped down to or below the critical load for forest ecosystems. But what remained from several decades of high acid deposition as a “residual pollution” is substantial soil acidification and levelling of soil reaction in a very acid range. The amount of this man-made acidification can be assessed by the compa­rison of actual soil analyses with historic ones (measurements of Frank, 1927). This reveals that at all non-carbonatic soils substantial acidification occurred with pH-decreases between 1.5 and 2.5 pH-values on most substrates. Only the podsols on Granite displayed a pH-decrease < 1 pH-value. The shape of the frequency distributions indi­cates that the variation of pH-values got much narrower with soil acidification. Thus most of the natural diversity of chemical site conditions was lost within 65 years of soil acidification. For all carbonate-free substrates almost all pH-values in the upper mineral soil are below the pH threshold limiting the abundance of endogaeic earthworms. Soil protective liming was conducted in the state of Baden-Württemberg since the early 1980ies with the aim to neutralize actual acid deposition. This argument got obsolete due to the reduction of acid depo­sition to a tolerable degree. But the unnatural acidification status of the soils remained as an unsolved environmental problem. The concept of soil regenerative liming intends to reduce the acidity stored in the mineral soils, mainly as Al3+ ions. Thus the site specific need of lime for approximating the natural soil chemical status has to be assessed in order to direct the new liming concept adequately. We used the amount of Al3+ stored in the subsoil (60-90cm) as indicator for the amount of stored acidity originating from acid deposition. This approach is justified in comparably young soils like in South-West Germany. There we can expect that almost all Al3+ in the subsoil is caused by anthropogenic deposition, since natural soil acidi­fication is bound to organic acids which are only active in the upper 2-5 decimetres of the soil. Soil protective liming does result in an increase of pH and base saturation (BS) in the upper soil. This provides better living conditions for earth worms as observed 6 years after liming with 10 t/ha in a liming experiment. The earth worms produce highly continuous biopores enhancing the aeration of the soil measured in terms of the relative apparent gas diffusion coefficient (Ds/Do). The open aggregate structure and en­hanced gas diffusivity provide more favourable conditions for root propagation. The depth of the intensively rooted soil zone was found to be increased by about 100% in long-term liming experi­ments, set up in the 1950ies. Until a depth of 35cm the limed plot showed significantly higher fine root densities as the control.

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last modified 2014-04-04