Soil microbiota resilience in a two-decade long-term experiment comparing an organic and a conventional cropping system

The effect of conventional and organic management in agriculture impacts not only economic and food quality aspects but potentially all biological components of the environment where these activities occur, including soil microorganisms. While there is generally positive appreciation for organic agriculture's role in organic matter accumulation, its beneficial effects on soil microbiota are a matter of debate, mostly due to the varying conditions in which the comparisons are made. To minimize the impact of distant locations, soils were sampled from nearby fields managed separately with the same rotation schemes for 18 years with conventional low-impact and organic agriculture methods. Samples from six different crops were compared using metabarcoding and metabolomic fingerprinting. The major differences were found between late summer and spring, whereas the variations between the beginning and the end of the spring were neither large nor significant. Some significant differences were found between the microbiota of organic vs. conventional management, particularly between r- and k-strategist microorganisms. While other studies found very little differences between microbiota of differently managed soils after shorter time periods, this work highlights that nearly two decades of separate management are necessary to induce significant variations in the microbiota. This suggests a strong resilience of soil populations and the need for very long-term strategies in agriculture to effect significant changes in soil quality.