Compacted subsoils in organic farming: Mechanical loosening and the risk of recompaction

Summary

Many soils already exhibit harmfully compacted subsoils. For these soils, improvement of the present poor subsoil structure is needed. Our study showed that biological amelioration comprises a favourable alternative to mechanical subsoiling. Root and earthworm channels constitute effective pathways through compacted layers and significantly improve soil functions like aeration, infiltration and deep rooting. Already, organic farming promote earthworm activity due to the use of diverse crop rotations, catch crops and organic amendments. However, also in organic farmed systems, substantial changes in soil management may be needed to significantly enhance the number of channels in the subsoil. The changes in soil management may include simultaneous changes in tillage and traffic, crop rotation, and rate, type and timing of organic amendments. Exploring management strategies that secures a fast and persistent improvement of subsoil structure represents a great challenge for future research in organic farming.