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  • 1
    Electronic Resource
    Electronic Resource
    Penetration of soil aggregates of finite size (1986)
    Springer
    Plant and soil 94 (1986), S. 43-58 
    Details
    ISSN: 1573-5036
    Keywords: Aggregate size ; Blunt probe ; Penetrometer pressure ; Plastic failure ; Plastic front ; Probe penetration ; Radial stress ; Root penetration ; Tangential stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Maximum penetrometer pressure was measured on artificial soil aggregates of finite size (2–29 mm) using blunt probes (total cone angle 60°) driven at 3 mm min−1. Maximum penetrometer pressure increased asymptotically with increase in dimensionless aggregate radius,b/a, wherea andb are the probe and aggregate radii, respectively. A theory was developed for penetration of blunt probes into soil aggregates of finite size. The theory assumed that plastic failure occurs out to a radius,R, and that beyond this only elastic straining occurs. This theory can be applied to estimate the radial and tangential stresses adjacent to a blunt probe. The estimated radial and tangential stresses increased with increase in dimensionless aggregate radius,b/a. The radius of the plastic front,R, around the probe is predicted to increase with increased aggregate size. The results also demonstrate the effect of soil shear cohesion and internal friction angle onR. The results are discussed with reference to root penetration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02380589
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  • 2
    Electronic Resource
    Electronic Resource
    Penetration of soil aggregates of finite size (1986)
    Springer
    Plant and soil 94 (1986), S. 59-85 
    Details
    ISSN: 1573-5036
    Keywords: Cohesion ; Gossypium hirsutum ; Helianthus annuus ; Penetrometer resistance ; Pisum sativum ; Plastic failure ; Radial stress ; Root diameter ; Root growth pressure ; Soil aggregates ; Tangential stress ; Tensile stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The axial force required for penetration of soil aggregates by roots of pea (Pisum sativum cv. Greenfeast), cotton (Gossypium hirsutum cv. Sicot 3) and sunflower (Helianthus annuus cv. Hysun) seedlings was measured. Effects of aggregate size and strength on root penetration behaviour were investigated. Maximum axial root growth pressure (P x ) was estimated from the maximum axial root growth force (F max) and mean root diameter. F max, time (T max) to attainF max, andP x all increased with increase in size and strength of aggregates. A significant interactive effect of size and strength of aggregate on root diameter was observed.F max,T max and root diameter were significantly different for different plant species. Maximum penetrometer pressure (P′) was compared with the axial pressures generated during root penetration. The penetrometer probe was found to overestimate the root growth pressure by a factor of 1.8 to 3.8.P x /P′ decreased with increase in size and strength of aggregates. A theory was developed to estimate radial and tangential stresses adjacent to the soil-root interface assuming cylindrical deformation by the root in aggregates of finite size. The stresses were calculated using shear cohesion values, estimated from tensile strength measurements, and with an assumed value of soil internal friction. Radial and tangential stresses adjacent to the root axis increased with increase in dimensionless aggregate radius and aggregate strength. Tensile stress adjacent to the root axis is predicted to result in plastic failure of finite sized aggregates during root penetration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02380590
    Location Call Number Expected Availability
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    Paper (German National Licenses)
    Fulltext
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