Effects of Agricultural Management on Water Retention via Changes in Organic Carbon in Topsoil and Subsoil

Background Increases in soil organic carbon (SOC) through agricultural management can alter soil water retention. This is determined via changes in pore size distribution, namely, air capacity (AC), plant‐available water capacity (PAWC), and hygroscopic water capacity (HWC). However, it is uncertain how much soil water retention in topsoil and subsoil can be increased with agricultural management practices. Aims The aim of this study was to quantify the influence of different agricultural management practices commonly used in Central Europe on AC, PAWC, and HWC in topsoil and subsoil as a result of SOC changes in different soil types. Methods We sampled topsoil and subsoil at 11 sites across Germany that showed a management‐induced SOC increase and a wide range of soil texture and measured the volumetric water content at different pressure heads from saturation to permanent wilting point. Results In topsoil, AC increased on average by 1.3 mm 100 mm −1 (+17%), PAWC by 1.6 mm 100 mm −1 (+8%), and HWC by 1.6 mm 100 mm −1 (+15%) per 10 g kg −1 increase in SOC. In subsoil, SOC was increased by incorporating compost or topsoil material, which increased AC by 10.0 mm 100 mm −1 (+134%), PAWC by 0.7 mm 100 mm −1 (+3%), and HWC by 0.5 mm 100 mm −1 (+7%) per 10 g kg −1 increase in SOC. The total average increase in PAWC was 1 mm in topsoil and 1 mm in subsoil, with SOC increases by 4 and 5 g kg −1 , respectively. Conclusions More than 50 years of additional farmyard manure addition resulted in an average SOC increase of 3.4 g kg −1 , but PAWC increased only slightly by 2.5%, showing the limited impact of agricultural management on water retention capacities.