A Soil Structure Observatory (SSO) to Study Structural Recovery of Compacted Soil By Natural Processes.

Agricultural soil compaction adversely impacts soil’s structure, productivity and ecological processes and thus is detrimental to crop growth and other ecosystem services. Traditionally, soil compaction studies focus on quantifying compaction mechanics and immediate impacts on soil traits, yet little is known about mechanisms and rates of natural soil structure recovery after compaction. These rates and recovery period reflect the extent and real costs of compaction damage. We launched a long-term soil structure observatory (SSO) to quantify post-compaction structural restoration at time scales of years to a decade. The SSO established on a loamy soil in Zurich, Switzerland, was designed to monitor key biophysical mechanisms that affect structure restoration of compacted soil, including effects of root and earthworm bioturbation, and abiotic wetting-drying, shrink-swell and freeze-thaw cycles. We implemented three compaction treatments – control, full surface compaction and wheel track compaction; on each we installed four cropping systems (bare soil, permanent grass, crop rotation – direct seeded, and crop rotation - conventional tillage)  replicated in three blocks. The crop rotation treatments enable assessment of soil structure regeneration rates under standard agricultural management practices. The soil initial conditions at the SSO were characterized pre- and post-compaction, and sensor banks were installed for continuous monitoring of soil water content and matric potential, temperature, CO₂ and O₂ concentrations, redox potential and oxygen diffusion rates. Periodic soil sampling and measurements and electrical resistivity tomography (ERT) and ground penetrating radar (GPR) imaging would provide insights into structural changes over time at profile and plot scales. The soil properties before and after compaction, show a significant decrease in infiltration rates (by 2 orders of magnitude); a clear decrease in measured soil O₂ with a concurrent increase in CO₂ values in compacted plots. SSO field observations will be supplemented by quantitative modeling and laboratory studies of key soil structure processes.