Summary
Pea, corn, and grass seedling root growth in five sands varying in grain-size distribution, packed dry and then maintained at six matric potentials, varied according to mechanical impedance and aeration.
Mechanical impedance restricted root elongation in every treatment including the finer dryer sands in which longest roots were found, but it was greatest in the coarse sands, where crooked swollen roots similar in shape to the pore channels were produced. Straight evenly tapered roots were formed in the fine sands due to a more balanced stress distribution over the root tip. Interpretations of penetrometer measurements differed in coarse and fine sands.
‘Aeration effects’ were distinguished from mechanical impedance effects by comparing the root lengths expected (mechanical impedance acting singly) with those actually obtained (mechanical impedance and aeration acting together), and they occurred in sands with less than 25 per cent gas-filled pore space. No effect due to water availability could be found.
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References
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Warnaars, B.C., Eavis, B.W. Soil physical conditions affecting seedling root growth. Plant Soil 36, 623–634 (1972). https://doi.org/10.1007/BF01373512
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DOI: https://doi.org/10.1007/BF01373512