Resistance of soil community against the onset of inversion tillage in fields under long-term minimum tillage and organic farming

Conventional inversion tillage is known to alter soil biota, yet the ecological effects of reintroducing occasional inversion tillage into long-term minimum tillage systems remain unclear. This study addressed this knowledge gap through a three-year field experiment conducted on two boreal organic cereal farms. At both sites, control plots remained under continuous minimum tillage, while treatment plots underwent inversion tillage with mouldboard ploughing. Ploughing was carried out in spring at one site and in autumn at the other, with immediate sowing after tillage to reduce bare soil exposure. Soil biological responses were evaluated annually across key soil organism groups: archaea, bacteria, fungi, nematodes, and earthworms. Multivariate analyses and generalized linear mixed models were used to assess the effects of tillage and environmental conditions. Overall, ploughing had only minor effects on soil community composition and diversity over the study period. Instead, year-to-year variability, likely driven by weather conditions, was a more influential factor shaping soil communities Some subtle, group-specific responses were observed among fungal and nematode communities, although these varied between years and depended on whether tillage occurred in spring or autumn. Autumn ploughing had the most immediate biological impact, reducing total earthworm biomass by 44%, largely due to a 53% decline in anecic earthworm density, and also lowering functional gene copy numbers ( ureC , nifH , nirK , cbbL ) in the last monitoring year. The findings suggest that occasional inversion tillage causes only limited disruption to soil biota in boreal systems, particularly when performed in spring, pointing to the importance of season of ploughing in minimizing ecological impacts.