Apparatus was developed to permit simultaneous study of the effects of two of the factors regarded as responsible for the poor growth of roots in some compacted soils. The other factors were purposely minimized by the use of glass beads and tap water as the substrate and sterilized, freshly germinated corn seedlings as the plant material. The factors investigated were mechanical impedance and oxygen supply to the root. Although the mechanical impedance imposed could not be precisely stated, the control of the soil atmosphere was excellent. It was found that the rate of growth of unimpeded roots declines when the oxygen content falls below 10% and that the growth of impeded roots is seriously reduced under these conditions. Microscopic examination of roots grown under conditions of severe mechanical restraint have not yet revealed reliable symptoms of impedance other than a distortion of the normal shape.
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Gill et al. (1956) studied this question.