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  • Compaction pan  (2)
  • Root diameter  (2)
  • Springer  (4)
  • 1985-1989  (4)
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  • Springer  (4)
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  • 1985-1989  (4)
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  • 1
    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
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  • 2
    Electronic Resource
    Electronic Resource
    Model experiments on the behaviour of roots at the interface between a tilled seed-bed and a compacted sub-soil (1986)
    Springer
    Plant and soil 95 (1986), S. 135-147 
    Details
    ISSN: 1573-5036
    Keywords: Compaction pan ; Crack Hexagonal cracks ; Parallel cracks Pea ; Pisum sativum ; Root entry ; Triticum aestivum Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Roots which grow down through a seed-bed and encounter a strong, untilled sub-soil beneath may be deflected horizontally. They will continue to grow horizontally along the top of the sub-soil either until the seed-bed dries out and the roots wilt and cease elongating, or until they find some path of low resistance down through the sub-soil. A major source of such paths is vertical cracks in the sub-soil. Model experiments were done with artificial impenetrable sub-soils containing parallel cracks with widths in the range 0.5–3 mm. Roots of pea and wheat were grown down through beds of aggregates to encounter the artificial sub-soil at random positions. The roots were deflected horizontally until they encountered the vertical cracks. The proportions of roots which entered the cracks were found to decrease strongly with decreasing crack width and increasing (more perpendicular) angle of incidence between the root and the crack. The experimental results were combined with the results from computer simulation studies which gave the proportions of roots encountering cracks at various angles with both hexagonal and parallel crack patterns. This showed that parallel crack patterns should enable a greater proportion of roots to enter the cracks than hexagonal crack patterns. Monocotyledonous plants which have several seminal root axes per plant have a statistical advantage over dicotyledonous plants which have only one seminal axis per plant with regard to crack entry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02378859
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  • 3
    Electronic Resource
    Electronic Resource
    Model experiments on the behaviour of roots at the interface between a tilled seed-bed and a compacted sub-soil (1986)
    Springer
    Plant and soil 95 (1986), S. 123-133 
    Details
    ISSN: 1573-5036
    Keywords: Aggregate ; Compaction pan ; Penetrometer ; Root penetration ; Seed-bed ; Soil strength ; Triticum aestivum ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary When elongating seminal roots of developing plants reach the base of a tilled seedbed, they often encounter a layer of dense, strong untilled soil. At this interface, they may be deflected horizontally and instead of penetrating the sub-soil, they may form a horizontal mat of roots at the base of the seed-bed. If this occurs, the plants are unable to absorb the reserves of water in the sub-soil, and are very sensitive to short periods of drought. Model experiments were done with artificial sub-soil layers having a range of strengths and with artificial seed-beds having sieved soil aggregates in the 4–7.7, 2–4 and 1–2 mm size ranges. Roots of wheat were grown through the aggregate beds and the proportions of roots which penetrated into the sub-soil were investigated as functions of sub-soil strength and diameter of the aggregates in the seed-bed. The proportion penetrating was found to decrease exponentially with sub-soil strength. The rate of decrease was similar for the 2–4 and 1–2 mm aggregates but was greater for the 4–6.7 mm aggregates. It is concluded that, provided that the roots of different plant species behave similarly, the base of the seed-bed should be composed of fine aggregates and that the penetrometer strength of the underlying untilled sub-soil should not exceed 0.4 MPa for plants with a single seminal axis or 3 MPa for plants such as wheat with 4 seminal axes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02378858
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  • 4
    Electronic Resource
    Electronic Resource
    Maximum axial and radial growth pressures of plant roots (1986)
    Springer
    Plant and soil 95 (1986), S. 315-326 
    Details
    ISSN: 1573-5036
    Keywords: Axial growth pressure ; Gossypium hirsutum ; Helianthus annuus ; Pisum sativum ; Radial growth pressure ; Root diameter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The axial root growth force exerted by seedlings of pea (Pisum sativum cv. Greenfeast), cotton (Gossypium hirsutum cv. Sicot 3) and sunflower (Helianthus annuus cv. Hysun) was measured. Effects of different seedling age and different batches of seeds on axial root growth pressure were investigated. Mean values of the maximum axial root growth pressure (Pa) estimated from the maximum axial root growth force (Fmax) and root diameter were 497, 289, and 238 kPa respectively for pea, cotton and sunflower seedlings of same size. Pa and Fmax were significantly influenced by seedling age and for pea seedlings of same age they varied with the seed batch. A new technique was developed for estimating radial root growth pressure and was tested on pea seedlings. Each pea root was confined both in the axial and radial directions in a cylindrical chalk sample at a constant water potential. The roots exerted radial stress which caused tensile failure in a proportion of the chalks. The measurement of tensile strength of duplicate chalks enabled estimation of the maximum radial pressures exerted by the roots. The maximum axial and radial root growth pressures were of comparable magnitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02374612
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