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  • 1
    Electronic Resource
    Electronic Resource
    An improved model of root growth in structured soil (1979)
    Springer
    Plant and soil 52 (1979), S. 325-343 
    Details
    ISSN: 1573-5036
    Keywords: Aggregate size ; Maize ; Nutrient uptake ; Root growth ; Soil strength ; Soil structrure ; Sorghum ; Soybean ; Stochastic model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The growth of roots of maize, sorghum and soybean is modelled through beds of spherical aggregates. Effects of aggregate size and strength, and effects of the spread or distribution of aggregate strengths are investigated. This is achieved by a combination of a statistical model for soil structure with a statistical model for the penetration behaviour of a root at a void/aggregate interface. It is shown that the behaviour of a root at such an interfac is dependent on the previous history of the root in its passage through the soil. It is concluded that the smaller the aggregate size, the greater is the nutrient availability per unit length of root. The influence of aggregate size decreases with increasing soil strength. An increase in aggregate strength reduces the availability of nutrients per unit length of root. However, the rate of nutrient uptake per root axis goes through a minimum at a strength (for maize) of around 80 per cent of the maximum limiting aggregate strength for root penetration. An increase in the spread of aggregate strengths usually results in a proportional increase in nutrient availability. This effect is more pronounced with smaller aggregate sizes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02185576
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  • 2
    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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  • 3
    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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  • 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
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Mechanics of root growth (1987)
    Springer
    Plant and soil 98 (1987), S. 303-312 
    Details
    ISSN: 1573-5036
    Keywords: Elongation ; Extensibility ; Mechanical stress ; Osmoregulation ; Soil strength ; Water stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A model is developed for the rate of elongation of a root tip in terms of the balance of pressures acting on the root. Differentials of this equation give expressions for the changes in root elongation rate with respect to soil water potential and soil mechanical resistance. The model predicts that root cells osmoregulate against both water stress and soil mechanical resistance with predicts that root cells osmoregulate against both water stress and soil mechanical resistance with similar efficiencies which are less than 100%. Analysis of published data leads to the conclusion that root tips of pea osmoregulate with 70% efficiency. A working equation is developed for the elongation rate of roots in conditions of combined water stress and mechanical resistance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02378351
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  • 8
    Electronic Resource
    Electronic Resource
    Behaviour of roots in cracks between soil peds (1983)
    Springer
    Plant and soil 74 (1983), S. 153-162 
    Details
    ISSN: 1573-5036
    Keywords: Cracks ; Crack orientation ; Elongation rate ; Pea ; Penetration ; Penetrometer ; Rape ; Roots ; Safflower ; Soil strength ; Soil structure ; Undisturbed soil
    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 growing over the surfaces of undisturbed soil clods and for roots growing along narrow cracks between two clods. Seminal roots of pea, rape and safflower were compared for a range of soil strengths and angles of inclination of the clod surfaces. For all three plant species, the ability of the roots to penetrate ped surfaces decreased with increasing soil strength and increasing angle of the surface relative to the horizontal. However, there was considerable variability of behaviour between roots. Roots were able to elongate more rapidly in cracks narrower than the root diameter than through undisturbed clods without cracks, provided that the crack was not orientated at an oblique angle to the preferred geotropic growth direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02143606
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