6,381 research outputs found
Biomechanical limits to soil penetration by earthworms: direct measurements of hydroskeletal pressures and peristaltic motions
No full textBurrows resulting from earthworm activity are important for supporting various physical and ecological soil processes. Earthworm burrowing activity is quantified using models for earthworm penetration and cavity expansion that consider soil moisture and mechanical properties. Key parameters in these models are the maximal pressures exerted by the earthworm's hydroskeleton (estimated at 200 kPa). We designed a special pressure chamber that directly measures the pressures exerted by moving earthworms under different confining pressures to delineate the limits of earthworm activity in soils at different mechanical and hydration states. The chamber consists of a Plexiglas prism fitted with inner flexible tubing that hosts the earthworm. The gap around the tubing is pressurized using water, and the earthworm's peristaltic motion and concurrent pressure fluctuations were recorded by a camera and pressure transducer. A model that links the earthworm's kinematics with measured pressure fluctuations was developed. Resulting maximal values of radial pressures for anecic and endogeic earthworms were 130 kPa and 195 kPa, respectively. Mean earthworm peristaltic frequencies were used to quantify burrowing rates that were in agreement with previous results. The study delineates mechanical constraints to soil bioturbation by earthworms by mapping the elastic behaviour in the measurement chamber onto the expected elasto-viscoplastic environment of natural soils.</p
Soil Penetration by Earthworms and Plant Roots--Mechanical Energetics of Bioturbation of Compacted Soils.
No full textWe quantify mechanical processes common to soil penetration by earthworms and growing plant roots, including the energetic requirements for soil plastic displacement. The basic mechanical model considers cavity expansion into a plastic wet soil involving wedging by root tips or earthworms via cone-like penetration followed by cavity expansion due to pressurized earthworm hydroskeleton or root radial growth. The mechanical stresses and resulting soil strains determine the mechanical energy required for bioturbation under different soil hydro-mechanical conditions for a realistic range of root/earthworm geometries. Modeling results suggest that higher soil water content and reduced clay content reduce the strain energy required for soil penetration. The critical earthworm or root pressure increases with increased diameter of root or earthworm, however, results are insensitive to the cone apex (shape of the tip). The invested mechanical energy per unit length increase with increasing earthworm and plant root diameters, whereas mechanical energy per unit of displaced soil volume decreases with larger diameters. The study provides a quantitative framework for estimating energy requirements for soil penetration work done by earthworms and plant roots, and delineates intrinsic and external mechanical limits for bioturbation processes. Estimated energy requirements for earthworm biopore networks are linked to consumption of soil organic matter and suggest that earthworm populations are likely to consume a significant fraction of ecosystem net primary production to sustain their subterranean activities
The physical structure of soil: Determinant and consequence of trophic interactions
No full textISSN:0038-0717ISSN:1879-3428ISSN:1879-342
Soil bioturbation by earthworms and plant roots: mechanical and energetic consideration for plastic deformation
No full textSoil structure is a key factor shaping hydrological and ecological functions including water storage, deep recharge and plant growth. Compaction adversely impacts soil ecosystem services over extended periods (years to decades) until structure and functionality are restored. An important class of soil structural restoration processes are related to biomechanical activity associated with borrowing of earthworms and root proliferation in impacted soils. This study employs a new biomechanical model to estimate stresses required for earthworm and plant root bioturbation under different conditions and the mechanical energy required. We consider steady state plastic cavity expansion to determine burrowing pressures of earthworms and plant roots as linked with models for cone penetration required for initial burrowing into soil volumes. We use earthworm physical and ecological parameters (e.g., population density, burrowing rate, and burrowing behavior) to convert mechanical deformation to estimation of energy and soil organic carbon (energy source for earthworms). Results illustrate a reduction in strain energy with increasing water content and trade-offs between pressure and energy investment for various root and earthworm geometries and soil hydration. The study provides a quantitative framework for estimating energy costs of bioturbation in terms of soil organic carbon or plant assimilates and delineates mechanical and hydration conditions that promote or constrain such activities
Global earthworm distribution and activity windows based on soil hydromechanical constraints
No full textISSN:2399-364
Experimental evaluation of earthworm and plant root soil penetration–cavity expansion models using cone penetrometer analogs
No full textRecent mechanical models of soil penetration by earthworms and plant roots based on penetration-cavity expansion were tested using cone penetration measurements at scales compatible with the sizes of earthworms and plant roots. Measurements using different cone radii (1.0–2.5 mm) and cone semi-apex angles (15–30°) were obtained for a range of soils and water contents at highly resolved penetration forces and constant insertion rates. The cone penetration measurements were interpreted using independently determined soil mechanical parameters and yielded good agreement with predictions from an analytical mechanical model. Experimental confirmation of penetration force predictions supports estimates of energy costs associated with soil bioturbation that vary with soil hydration status and mechanical characteristics. Effects of soil friction and axial compaction were assessed by comparing the results from conventional and recessed cones (to eliminate soil–shaft friction). The study provides new insights into quantitative soil bioturbation processes and expands predictive capabilities of the mechanics and energetics of earthworm activity and root zone dynamics related to soil structure development
Mechanics and energetics of soil penetration by earthworms and plant roots: higher rates cost more
No full textWe quantified the mechanics and energetics of soil penetration by burrowing earthworms and growing plant roots considering different penetration rates and soil mechanical properties. The mechanical model considers cavity expansion by cone-like penetration into a viscoelastic soil material in which penetration rates affect the resulting forces and hence the mechanical energy required. To test the predicted penetration rate effects on forces and energetics, we conducted rate-controlled cone penetration experiments across rates ranging from 1 to 200 μm s−1 to determine the mechanical resistance forces for cone geometries similar to plant roots and earthworms. These measurements also enabled inverse estimation of soil rheological parameters that were in good agreement with literature values for similar soils and water contents. The results suggest that higher soil penetration rates typical for earthworm activity (about 200 μm s−1) may significantly increase resistance forces and energy expenditure by up to threefold relative to slower penetration rates of plant roots (0.2 μm s−1) for similar soil properties and geometries. Another important mechanical difference between earthworms and roots is the radial pressures that earthworms’ hydro-skeleton exerts (<230 kPa), whereas plant roots may exert radial pressures exceeding 1 MPa. These inherent differences in burrowing rates and expansion pressures may significantly extend the range of conditions suitable for root growth in drier and compacted soil compared to earthworm activity. Results suggest that the mechanical energy costs of soil bioturbation under agricultural intensification and drier climate could greatly increase the energetic costs of these ecologically important soil structure-forming bioprocesses
Soil penetration by earthworms and plant roots – different rates and energy requirements
No full textExperimental Verification of penetration-cavity expansion models for earthworm bioturbation using special cone penetrometers
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