Factors which influence the ability of plant roots and earthworms to penetrate soil are reviewed. Plant factors include the hydraulic conductivity, yield stress and extensibility of the cell walls and the osmotic potential of the cell contents. Earthworm factors include the tensions than can be generated by the longitudinal and circular muscles. Soil factors include the penetration resistance and water potential, both of which are strongly dependent on soil water content.
In structured soils, the ability of a root to penetrate a soil structural unit is controlled largely by the length of the void space it has just crossed. This is because the maximum axial stress that the root can generate may be limited by its buckling stress and not by its potential maximum growth pressure. Soil strength and structure both influence root morphology and the root environment.
Roots and earthworms play key roles in generating soil structure. Root channels and earthworm tunnels provide pathways for water infiltration, gas exchange and for rapid penetration by roots of subsequent crops. Water extraction by roots results in desiccation of the soil, cracking and aggregate formation. Earthworm casts can become stable soil aggregates if left undisturbed.
These natural processes of root penetration and earthworm activity can result in “good”; soil structures that allow rapid water infiltration, good storage of water, good aeration and good rootability. Such soils will usually have greater productivity than soils where structure has been damaged or destroyed. Biological tillage by plant roots and earthworms provides a valuable and important input towards the maintenance of a sustainable and productive soil resource.
Whalley, W.R.; Dexter, A.R. Root development and earthworm movement in relation to soil strength and structure. Archives of Agronomy and Soil Science (1994) 38 (1) 1-40. [DOI: 10.1080/03650349409365834]