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  • Pisum sativum  (5)
  • Wheat  (5)
  • Mechanical Engineering  (4)
  • 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. 149-161 
    Details
    ISSN: 1573-5036
    Keywords: Compaction pan Earthworms ; Pea ; Pisum sativum ; Root channels ; Root entry ; Trematotropism ; Triticum aestivum ; Tunnels ; 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 unable to penetrate the sub-soil and 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. Such paths are often cylindrical biopores such as earthworm tunnels or channels left after the decay of previous root systems. Model experiments were done with artificial impenetrable sub-soils containing arrays of round holes of various diameters. Roots of pea and wheat were grown down through beds of aggregates to encounter the artificial sub-soils at random positions. The roots were deflected horizontally until they encountered the vertical holes. The proportions of roots which entered the holes were found to decrease with decreasing hole diameter. Computer simulation studies were done to investigate some aspects of roots encountering impenetrable sub-soils containing random arrays of round holes. The distances that randomly-deflected roots would have to travel before encountering holes were studied as functions of hole diameter and hole density. The experimental results were combined and compared with the results from the computer simulations. It was found that the numbers of roots encountering holes within certain distances in practice were not significantly different from those simulated on the basis of random chance. Therefore there was no evidence for the roots sensing and growing preferentially towards the holes (trematotropism) in the well-aerated system used in the experiments. However, limited evidence shows that the possibility of trematotropism cannot be ruled out for poorly-aerated systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02378860
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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    The behaviour of roots encountering cracks in soil (1984)
    Springer
    Plant and soil 79 (1984), S. 11-28 
    Details
    ISSN: 1573-5036
    Keywords: Beta distribution ; Buckling ; Cracks ; Crack width ; Lateral roots ; Pea ; Penetration ; Penetrometer ; Rape ; Remoulded soil ; Roots ; Safflower ; Seminal axes ; Soil strength ; Undisturbed soil ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary It is shown that probabilities of root penetration across cracks in soil can be calculated effectively using a mathematical model involving root stress and soil distributions and penetrometer/root stress ratios. Penetration criteria are developed, and it is found that the effective penetrometer/root stress ratios take values of about 4 for crack widths smaller than about 2 mm and about 8 for wider cracks. Root swelling does not appear to contribute significantly to the probability of root penetration through any effect on root buckling stress. Suggestions are made for further work on the effects of soil structure and strength on root behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02182140
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  • 7
    Electronic Resource
    Electronic Resource
    Mechanics of root elongation and the effects of 3,5-diiodo-4-hydroxybenzoic acid (DIHB) (1987)
    Springer
    Plant and soil 99 (1987), S. 211-218 
    Details
    ISSN: 1573-5036
    Keywords: Aeration ; Barley ; 3,5-Diiodo-4-hydroxybenzoic acid ; Extensibility ; Mechanical impedance ; Osmotic potential ; Pea ; Root elongation ; Wheat ; Young's modulus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary This paper reports the results of two series of experiments. In the first the effects of DIHB on the rate of root elongation were compared on unstressed roots and on roots stressed by mechanical impedance and by inadequate levels of aeration. Barley plants were grown in beds of small glass spheres through which nutrient solution was circulated. Mechanical impedance of 25 kPa was applied by subjecting the beds to a confining pressure. Inadequate aeration was obtained by reducing the oxygen concentration in the nutrient solution to 5%. The second series examined possible effects of DIHB on the elastic modulus of root tips of wheat and pea. Elastic modulus gives an indication of the behaviour of roots in structured soil where penetration of peds can be limited by the buckling of root tips. The elastic modulus was measured in experiments of the static cantilever type on roots previously immersed in solutions of polyethylene glycol of different osmotic potential. Elastic modulus measurements can also detect any changes in turgor pressure and wilting characteristics of roots and can therefore help to identify the mechanisms of action of DIHB. DIHB caused increases in root elongation relative to controls in all cases: 26±5.7% in unstressed roots, 14±6.4% in mechanically impeded roots and 54±9.8% in roots growing in 5% oxygen. DIHB had no effect on the elastic modulus, osmotic or turgor pressure of the roots. It is concluded that DIHB acts by modifying the cell wall extensibility factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02370868
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  • 8
    Electronic Resource
    Electronic Resource
    The behaviour of roots encountering cracks in soil (1984)
    Springer
    Plant and soil 77 (1984), S. 141-149 
    Details
    ISSN: 1573-5036
    Keywords: Cracks ; Crack width ; Lateral roots ; Pea ; Penetration ; Penetrometer ; Rape ; Remoulded soil ; Roots ; Safflower ; Seminal axes ; Soil strength ; Undisturbed soil ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Experimental methods are described for observing the behaviour of roots encountering cracks in soil. The proportions of roots which enter a second soil block after crossing a crack of known width were measured. Soil strength was measured with a penetrometer. Results are presented for the proportions of seminal roots of wheat and primary lateral roots of pea which enter moulded soil of various strengths after crossing cracks. Results are also presented for the proportions of seminal roots of pea, rape and safflower which enter undisturbed soil after crossing cracks. It was found that, in all cases, the proportion of roots penetrating the second soil block decreased with increasing crack width and increasing soil strength. Also, a smaller proportion of thinner roots penetrated the second soil block than thicker roots under similar conditions. Root diameter in the cracks was influenced by both crack width and soil strength, and an empirical equation is presented to describe this effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02182918
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  • 9
    Electronic Resource
    Electronic Resource
    The temperature-dependence of the maximum axial growth pressure of roots of pea (Pisum sativum L.) (1994)
    Springer
    Plant and soil 163 (1994), S. 211-215 
    Details
    ISSN: 1573-5036
    Keywords: cell wall tension ; maximum axial growth pressure ; mechanical impedance ; Pisum sativum ; temperature-dependence ; turgor pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Although it has been suggested that the maximum axial growth pressure of roots is temperature-dependent, this has not previously been tested experimentally. In this paper we report the temperature-dependence of the maximum axial growth pressure of completely mechanically-impeded roots of pea (Pisum sativum L. cv Meteor). Maximum growth pressures were somewhat lower at 15 and 20°C than at 10, 25 or 30°C, but there was no overall trend for maximum growth pressure to increase or decrease with temperature. Turgor pressure in unimpeded roots varied little with temperature and we suggest that cell wall tension in completely impeded roots also varies little with temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00007970
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  • 10
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    Composite Structures and Materials Research at NASA Langley Research Center (2003)
    In:  CASI
    Details
    Publication Date: 2018-06-28
    Description: A summary of recent composite structures and materials research at NASA Langley Research Center is presented. Fabrication research to develop low-cost automated robotic fabrication procedures for thermosetting and thermoplastic composite materials, and low-cost liquid molding processes for preformed textile materials is described. Robotic fabrication procedures discussed include ply-by-ply, cure-on-the-fly heated placement head and out-of-autoclave electron-beam cure methods for tow and tape thermosetting and thermoplastic materials. Liquid molding fabrication processes described include Resin Film Infusion (RFI), Resin Transfer Molding (RTM) and Vacuum-Assisted Resin Transfer Molding (VARTM). Results for a full-scale composite wing box are summarized to identify the performance of materials and structures fabricated with these low-cost fabrication methods.
    Keywords: Mechanical Engineering
    Type: Low Cost Composite Structures and Cost Effective Application of Titanium Alloys in Military Platforms; 17-1 - 17-11; RTO-MP-069(II)
    Format: text
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    NASA TECHNICAL REPORTS
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