Long-term effects of conventional and reduced tillage on soil structure, soil ecological and soil hydraulic properties

There is a long-lasting debate about the effects of tillage practices on soil structure and structure-mediated ecosystem properties like hydraulic conductivity and crop productivity. This is investigated in a long-term field experiment on tillage practices at the Westerfeld trial in Bernburg, Germany (25 years of different management). Here we combine soil structure information obtained by X-ray microtomography with bulk properties like bulk density, air capacity and saturated hydraulic conductivity, as well as integrative, ecological properties like earthworm abundance and crop yield. This study goes beyond previous studies in that the soil microstructure is investigated in two different depths, within (13–23 cm) and underneath (28–38 cm) the plow horizon. Furthermore the microstructure is investigated at two different resolutions (60 μm and 20 μm) by employing a nested sampling design.The plowed horizon in the conventional tillage plots differs from the undisturbed soil underneath the cultivator depth (13–23 cm) in the reduced tillage plot by lower bulk density, higher air capacity, higher saturated hydraulic conductivity, higher macroporosity and pore connectivity. After 25 years of reduced tillage saturated hydraulic conductivity only marginally recovered in the abandoned plow pan (28–38 cm). Macropore density and connectivity did not change significantly as compared to the current plow pan under conventional tillage. The topsoil underneath the cultivator depth in the reduced tillage plot developed a “no-till pan”, as porosity and pore connectivity where smaller than in greater soil depths. Image-based macroporosity and laboratory-based air capacity showed good agreement.Overall, the combination of hydraulic measurements and X-ray CT imaging of soil microstructure at different resolutions provides a comprehensive view on soil structure modification by tillage practices. The change from conventional to reduced tillage led to a compaction of soil that was not compensated by higher bioturbation as reported for other sites. This is explained by unfavorable conditions for anecic earthworms (frequent dry periods with severely impaired penetrability of the loess substrate) as well as the absence of very deep rooting, perennial crops in crop rotation.