Mechanical Soil Database – Part II: Dependence of air conductivity on soil texture, type, structure, and cohesion: Results from a database obtained over three decades

Abstract

Air conductivity (Ka) and its dependency on pore continuity and diameter is an essential factor to quantify soil quality. The database SOILMECHDAT-Kiel contains parameters of undisturbed soil samples from over 500 profiles in Central Europe that have been collected and analyzed always with the same methods over 3 decades (1990–2020). Selected data (1990 – 2015) from the database were differentiated into topsoil and subsoil under conventional soil management at a matric potential of pF 1.8, clay content, soil type and structure. Between 1990 and 2015, there was a decrease in air conductivity (Ka) in subsoils, irrespective of soil texture and structure. The decrease in conductivity correlated most strongly with the clay content in the subsoil. In both sandy (clay 12%), a particularly strong decrease was recorded. Between 190 and 2015, the Ka of these soils was near the critical value of 5.5 × 10−4 m s−1. Taking the soil type and organic matter into account, the clay-rich subsoils (Bt-horizons) of Luvisols in particular showed a significant decrease in Ka, too. We conclude that decreasing Ka over 25 years, especially in clay-rich subsoils, is strongly influenced by conventional soil management by low organic matter and insufficient soil structure. In addition, all subsoils exhibit critical Ka values over the entire time period. However, sandy soils also exhibit significant conductivity losses, especially in the subsoil.