Effects of liming on soil structure and GHG fluxes at three spruce sites in SW Germany

<p>Forest soils in Central Europe received massive atmospheric deposition of SO<sub>2</sub> and NO<sub>x</sub> during the second half of the 20<sup>th</sup> century. The resulting fast acidification of the soils was accompanied by massive forest dieback and problematic nutrient imbalances at some sites. After the emissions of SO<sub>2</sub> have been reduced in the 80´s and 90´s, the situation of acidic deposition has been gradually improving. Yet, the deposition of N compounds remains high and still has an impact on forest ecosystems. Natural soil development and “regeneration” is a slow process, which is why other options were investigated to recover heavily affected forest soils. A well-known means to mitigate the observed effects of the anthropogenic acidification surges is liming, i.e. the application of minerals such as CaCO<sub>3</sub> and CaMg(CO<sub>3</sub>)<sub>2</sub> that are able to buffer strong acids. Liming directly affects soil pH which is a “master variable” of the soil. Soil pH, and thus, liming, affects and interacts with many soil processes from mineralization of organic matter and humification, to (de-) stabilization soil structure, nutrient availability and mobility, plant growth and more.</p><p>Several study sites were established in the 1980 in Baden-Wuerttemberg to study long term effects of liming on soil structure and forest growth. At all sites a “control” plot and a “limed” plot were established next to each other. The limed plots were treated with approx. 3 t ha<sup>-1</sup> of CaCO<sub>3</sub> in the 1980´s and 6 t ha<sup>-1</sup> of Ca/MgCO<sub>3 </sub>in 2003. Here we report on results from three sites (Bad Waldsee, Hospital, Herzogenweiler) with Spruce stands (70-110 years), where long term effects of liming on the physical soil structure and soil gas profiles (2017-2019) were studied (Jansone et al., 2020). Liming resulted in a reduction of the thickness of the humus layer and a blurring of the previously clearly separated boundary between the mineral soil and the humus layer. Even though total pore space in the top soil was slightly reduced at the limed plots, soil gas diffusivity was higher at a given air-filled pore-space. This indicates a better connectivity in the air-filled pores, that means more larger pores connecting the atmosphere at the soil surface and the mineral soil. Soil CO<sub>2</sub> concentrations showed clear seasonal patterns and a typical increase with depth. Higher CO<sub>2</sub> concentrations tend to be found in the un-limed control plots. Soil CH<sub>4</sub> concentrations at the soil–humus interface were closer to atmospheric concentrations in the limed plots compared to the control plots. This can be interpreted as an effect of the decrease in the thickness of the humus layer and the increase in the soil gas diffusivity (better aeration) or in a reduced activity of the methanotrophic community.</p><p> </p><p>Acknowledgement</p><p>This research was financially supported by Bundesministerium für Ernährung und Landwirtschaft (BMEL), grant number 28W-B-4-075-02 (2018–2021).</p><p><em>Literature</em></p><p><em>Jansone, L., von Wilpert, K. and Hartmann, P., 2020. Natural Recovery and Liming Effects in Acidified Forest Soils in SW-Germany. Soil Systems, 4(38): 1-35.</em></p>