Liming leads to changes in the physical properties of acidified forest soils

Background Forest liming is a common practice in many German forests, which aims primarily at improving soil chemical properties that have been negatively impacted by acid rain. Effects on physical functions have not yet been studied widely. Aims The hypothesis of this study is that chemical changes after liming lead to changes in the physical properties of the humus layer and mineral soil. Methods We studied soil physical characteristics (water retention characteristics, air and water permeabilities, and conductivities) of limed and adjacent control plots of sandy to loamy, acidified soils under spruce and beech‐dominated stands. Results We found differences between limed and control plots, especially in the humus layer and mineral top soil. Here, air capacity values (representing air‐filled macropores at −6 kPa) have experienced an increase, while available water capacities (representing the sum of dewatered mesopores between −6 and −1500 kPa) were reduced to a variable extent. These changes in pore size distributions affected gas diffusion as well as gas permeability positively. Unsaturated hydraulic conductivity was not affected. Below the top mineral soil, a tendency to a reduced macroporosity and gas permeability was observed, but no clear changes were detected. Conclusions Small but significant changes of soil physical properties and functions in the humus layer and top mineral soil are discussed to be an indirect effect of forest liming. Liming improves pH and nutrient availability, which in turn should have stimulated activity and abundance of soil fauna, especially earthworms. Where observed, their activity could explain the observed changes in soil physical properties. We believe that effects below the top soil might be due to mobilization and translocation of soil particles and a clogging of pores, but these depths were only studied at three plots. Compared to common liming practices, however, the investigated sites are characterized by significantly higher lime applications. The effects on practice liming areas in forestry praxis are therefore likely to be smaller than in this study.