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  • 1
    Electronic Resource
    Electronic Resource
    Penetration of very strong soils by seedling roots of different plant species (1991)
    Springer
    Plant and soil 135 (1991), S. 31-41 
    Details
    ISSN: 1573-5036
    Keywords: penetrometer resistance ; plant species ; root diameter ; root elongation ; seedling roots ; soil strength
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The abilities of seedling roots of twenty-two plant species to penetrate a strong growth medium were compared under controlled conditions. Seedlings were grown for 10 days in compression chambers filled with siliceous sandy soil at 0.2 kg kg−1 water content and mean penetrometer resistance of 4.2 MPa. Root elongation and thickening were measured after growth. The results show that soil strength reduced the elongation of roots of all plant species by over 90% and caused the diameters of the roots to increase compared with control plants grown in vermiculite (0 MPa resistance). Differences in both root elongation and root diameter were observed among plant species. Generally, the roots of dicotyledons (with large diameters) penetrated the strong medium more than graminaceous monocotyledons (with smaller diameters). There was a significant positive correlation (r=0.78, p〈0.05) between root diameter and elongation over all the species in the stressed plants. The species were ranked according to the relative root elongation and relative root thickening. Based on this ranking, lupin (Lupinus angustifolius), medic (Medicago scutelata) and faba bean (Vicia faba) were the species with the greatest thickening and elongation while wheat (Triticum aestivum), rhodesgrass (Chloris gayana) and barley (Hordeum vulgare) had the least. The weight of the seeds did not seem to influence either the thickening or elongation of the roots.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00014776
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  • 2
    Electronic Resource
    Electronic Resource
    Growth of seedling roots in response to external osmotic stress by polyethylene glycol 20,000 (1992)
    Springer
    Plant and soil 143 (1992), S. 85-91 
    Details
    ISSN: 1573-5036
    Keywords: plant species ; polyethylene glycol (PEG) ; osmotic potential ; osmotic stress ; root elongation ; root diameter ; seedling roots
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Seedling roots of ten plant species were grown in siliceous sand wetted with solutions of polyethylene glycol (PEG) of MW=20,000 with osmotic potentials of 0.0, − 0.25, − 0.5 and − 1.0 MPa. After 48 h growth under controlled lighting, root elongation and root diameter were measured. Root elongation of all species was reduced by increasing levels of external osmotic stress. Dicotyledonous species were affected more than monocotyledons at potentials of − 0.25 and − 0.5 MPa but less at − 1.0 MPa. Root diameters of all the species were thicker than those of the unstressed at potentials of − 0.25 and − 0.5 MPa. At a potential of − 1.0 MPa the dicotyledons were still thicker, though not by as much as they were at − 0.25 and − 0.5 MPa. The monocotyledons, in contrast, were thinner at − 1.0 MPa. There was a significant positive correlation (r=0.81, p 〈0.01) between root diameter and root elongation at − 1.0 MPa potential. Species were ranked according to the relative root elongation (RRE) and relative root thickness (RRT) at the highest level of stress (− 1.0 MPa). In both rankings dicotyledonous species were in the top ranks and monocotyledous species were in lower positions. The results are compared with those for the elongation and thickening of roots growing against external mechanical stress obtained in a previous study. There were good correlations between the responses observed for the two types of external stress. The implications of these findings are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00009132
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of root diameter on the penetration of seminal roots into a compacted subsoil (1992)
    Springer
    Plant and soil 144 (1992), S. 297-303 
    Details
    ISSN: 1573-5036
    Keywords: penetration resistance ; plant species ; root diameter ; soil compaction ; soil strength ; tillage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A field experiment was conducted to evaluate the influence of root diameter on the ability of roots of eight plant species to penetrate a compacted subsoil below a tilled layer. The soil was a fine sandy loam red-brown earth with a soil strength of about 3.0 MPa (at water content of 0.13 kg kg-1, corresponding to 0.81 plastic limit) at the base of a tilled layer. Relative root diameter (RRD), which was calculated as the ratio of the mean diameters of roots of plants grown in compacted soil to the mean diameters of those from uncompacted soil, was used to compare the sensitivity of roots to thicken under mechanical stress. Diameters of root tips of plants grown in soil with a compacted layer were consistently larger than those from uncompacted soil. Tap-rooted species generally had bigger diameters and RRDs than fibrous-rooted species. A higher proportion of thicker roots penetrated the strong layer at the interface than thinner roots. There were differences between plant species in the extent to which root diameter increased in response to the compaction. The roots which had larger RRD also tended to have higher penetration percentage. The results suggest that the size of a root has a significant influence on its ability to penetrate strong soil layers. It is suggested that this could be related to the effects which root diameter may have on root growth pressure and on the mode of soil deformation during penetration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00012888
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  • 4
    Electronic Resource
    Electronic Resource
    Modification of soil aggregation by watering regime and roots growing through beds of large aggregates (1994)
    Springer
    Plant and soil 160 (1994), S. 57-66 
    Details
    ISSN: 1573-5036
    Keywords: aggregation ; large aggregates ; plant species ; root growth ; soil watering regimes ; wetting and drying
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The influence of root growth and soil watering regime on aggregation was studied under controlled conditions. The study examined the influence of pea (Pisum sativum cv Greenfeast), ryegrass (Lolium rigidum cv Wimmera) and wheat (Triticum aestivum cv Kite) roots on changes in aggregation and on the properties of the aggregates. The soil was a non swelling red-brown earth which was either kept wet or was allowed to wet and dry during the experiment. Root growth increased the percentage of small sized aggregates (〈18 mm diameter), organic carbon, tensile strength and stability of aggregates in comparison with a non planted soil. Changes in aggregate size distribution and properties of the aggregates were related to root length density of the species and also to the soil watering regime. Root length density was in the order ryegrass〉pea〉wheat. Wetting and drying of soil increased the strength and stability of aggregates. Incubating aggregates allowed some roots to decompose but did not increase the strength or stability of aggregates compared with unincubated soil. The results of this experiment are of practical significance in soil structural management, and in studies of soil aggregation dynamics. It may be possible to use plant roots to alter the size and properties of aggregates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00150346
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  • 5
    Electronic Resource
    Electronic Resource
    Formation of aggregates by plant roots in homogenised soils (1992)
    Springer
    Plant and soil 142 (1992), S. 69-79 
    Details
    ISSN: 1573-5036
    Keywords: aggregates ; minirhizotrons ; plant roots ; plant species ; soils ; water regime ; wetting and drying
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The influence of root growth and water regime on the formation of aggregates was studied in modified minirhizotrons under controlled conditions. Two soils, a black earth (67% clay) and a red-brown earth (19% clay) were ground and forced through a 0.5 mm sieve. Ryegrass, pea and wheat were grown for fifteen wetting and drying (wd) cycles for 5 months. Another set of minirhizotrons was not planted and served as a control. Measurements of aggregate size distribution (ASD), aggregate tensile strength (ATS), aggregate stability (AS), aggregate bulk density (ABD) and organic carbon (OC) were made on single aggregates of the 2–4 mm fraction. The results showed that aggregates of the black earth which has a high clay content and shrink/swell properties had more smaller aggregates with higher ATS, AS and ABD than those from the red-brown earth. It was also found that for both soils: (1) w/d cycles and higher root length density (RLD) increased the proportions of smaller aggregates and aggregate strength; (2) differences in the ability of the plant species to influence aggregation was evident and seemed to be related to the RLD. The RLD was in the order ryegrass 〉 wheat 〉 pea. Mechanisms likely to be involved in processes of aggregate formation and stabilization are discussed. They include cracking of soil due to tensile stresses generated during drying of a shrinking soil; changes in pore water pressure within the soil mass caused by water uptake by plant roots generating effective stresses; and biological processes associated with plant roots and root exudates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010176
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  • 6
    Electronic Resource
    Electronic Resource
    Field evaluation of laboratory techniques for predicting the ability of roots to penetrate strong soil and of the influence of roots on water sorptivity (1993)
    Springer
    Plant and soil 149 (1993), S. 149-158 
    Details
    ISSN: 1573-5036
    Keywords: compaction ; field evaluation ; plant species ; root penetration ; sorptivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The ability of two laboratory screening techniques to predict the abilities of roots of eight crop species to penetrate a compacted soil were evaluated and compared in a field experiment. A soil tilled to remove the effects of mechanical resistance was planted with the same species to serve as a control. Depth of root penetration, root density and the influence of the roots on the sorptivity of water were measured. Roots of all species penetrated deeper in the deep tilled than compacted soils. There were differences in the ability of roots of the species to penetrate the compacted soil. Generally dicotyledonous species had more roots penetrating to depth in both the compact and deep tilled soils. Within the main species classifications, lupin and safflower (dicotyledons) and oats and barley (monocotyledons) had the highest penetration into the compacted soil. Water sorptivities in the deep tilled soils were higher than those of the compact soil. Soil from planted treatments had higher sorptivities than soil which had not been planted. This is attributed to biopores left by the roots. Sorptivities of soils which had dicotyledonous species were generally higher than those of monocotyledons. The soil planted with safflower produced the highest sorptivity in the compacted layer (0.1–0.3 m). A comparison of the accuracy of the two laboratory screening methods in predicting the field penetration of roots suggest that the method involving mechanical stress was better than that involving osmotic stress. Relative root diameter was found to be a better indicator of the penetration ability of roots than relative root elongation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00016604
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