Development of soil mechanical stability during initial soil formation – from field to rhizosphere scale

Pre-consolidation stress is a measure of mechanical stability on the bulk soil scale while aggregate stability and penetration resistance measurements can be used to assess soil strength at the micro/root scale. Starting from initial soil deposition soil stability is expected to develop over time by processes like consolidation, shrinking-swelling, root reinforcement or exudation of mucilage by roots. We studied the development of soil stability over a cropping period from 2019-2024 in Bad Lauchstädt (Germany) where excavated plots were refilled with homogenized loam and sand and planted with two contrasting maize (Zea mays, L.) genotypes. On the field scale loam plots showed a distinct increase of pre-consolidation stress for the first three years while sand plots did not display any temporal pattern (Rosskopf et al. 2022a). In a second laboratory study employing the same homogenised substrates we investigated the combined effect of mucilage concentration and soil water content on penetration resistance PR (Rosskopf et al. 2022b). A stainless-steel cone resembling the maize root geometry was mounted on a high-precision material testing device and pushed through the remoulded soil samples to simulate root growth. Loam and sand were mixed with chia (Salvia hispanica, L.) seed mucilage at various concentrations and samples were adjusted to a range of water contents. Higher mucilage concentrations significantly lowered PR in the driest loam, thus reducing the energy cost of plant root growth whereas in moister conditions it had the opposite effect. In a third study we investigated the direct effect of root growth on local soil deformation in the rhizosphere using X-ray mCT measurements and digital image correlation (Rosskopf et al. 2025). We could show that the extent of the deformation zone depended on soil texture and genotype. Our results provide valuable information on soil stabilisation processes during initial soil formation and highlight the complex interaction of physical and biological stabilisation mechanisms on various scales.

Acknowledgments

This work was conducted within the framework of the Priority Program 2089, funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – 403627636.

References

Rosskopf, U., Uteau, D. & Peth, S. 2022a. Development of mechanical soil stability in an initial homogeneous loam and sand planted with two maize (Zea mays L.) genotypes with contrasting root hair attributes under in-situ field conditions. Plant and Soil, 478, 143–162.

Rosskopf, U., Uteau, D. & Peth, S. 2022b. Effects of mucilage concentration at different water contents on mechanical stability and elasticity in a loamy and a sandy soil. European Journal of Soil Science, 73, e13189.

Rosskopf, U., Uteau, D. & Peth, S. 2025. Deformation patterns around growing roots using X-ray CT and digital volume correlation. Geoderma, 464, 117613.