Evolution of topsoil structure after compaction with a lightweight autonomous field robot

Soil structure dynamics during a season depend on management practices and environmental factors. A lightweight autonomous robot (total mass: 3300–4100 kg, wheel load: 700–1200 kg, contact areas: 0.125 m², inflation pressures: 60–280 kPa) was used for sowing (October 2021) and weeding (May 2022) operations on an annually plowed sandy loam field. We took 579 cm³ soil cores at 10- to 18-cm depth in the crop area and wheel tracks before and after the operations to assess the impact from traffic and the potential recovery of topsoil structural properties. We measured air permeability and effective air-filled porosity in the laboratory, and X-ray CT scanned the samples to evaluate soil pore functionality. The first operation (conducted on a moist seedbed) had the largest impact, significantly compacting and reducing the air-filled porosity by 42% (from 0.21 to 0.12 m³ m⁻³) and decreasing air permeability by 75.8% (from 130 to 31.5 µm²). After 7 months, the crop area and wheel track showed signs of soil consolidation due to environmental factors but not decompaction. The second operation occurred on drier (water content 0.06 g g⁻¹), stronger soil conditions (degree of compactness 100.8%), and recompaction of the wheel track was not observed. Traffic in weak soils can result in seasonal topsoil compaction despite the lighter wheel loads. However, due to the milder impacts, recovery rates might be faster for lightweight machinery than for heavy tractors. Multi-season studies are needed to assess the real potential of lightweight robots to minimize soil compaction risk.