Changes in soil structure and aeration due to liming and acid irrigation

Biologic activity is one of the main factors controlling the floating equilibrium between loosening and compacting forces in humic forest soils. Therefore it can be expected that both acid deposition and compensatory liming indirectly influence the soil structure and soil aeration. To measure macro-pore structure, CO₂ concentrations in the soil air, and respiration rates we used naturally structured soil cores from the Höglwald forest-ecosystem research plots with experimental acid deposition and liming, but standardized water supply. Results are integrated in an one-dimensional soil-aeration model. Compared to the control plot, in the top soil of the limed plot both gaseous diffusion coefficients and respiration rates are increased. Since the CO₂ concentration in the soil air is decreased at the same time, the soil aeration status of the whole profile can be regarded as stabilized. On the acid irrigated plot, gas-diffusion coefficients are not significantly changed with regard to the control. In the top-mineral soil, in contrast to the working hypothesis, they are tendencially increased. In the case of liming, a stimulation of biologic activity and a positive feedback on the soil structure could be attributed to an increased earth-worm activity due in turn to decreased acidity and enhanced feeding conditions. The acid irrigation leads to increased Al³⁺ activity, which can stabilize the soil structure.