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Laboratory studies of the effect of soil impedance and soil moisture on root elongation of seedlings of Pinus radiata D.Don.

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Davis, G. R.(Gordon Richard) (1987) Laboratory studies of the effect of soil impedance and soil moisture on root elongation of seedlings of Pinus radiata D.Don. Coursework Master thesis, University of Tasmania.

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Abstract

In a drying soil root elongation rate often declines.
Whether the reduction in elongation is due to reduced soil
moisture or increased soil strength is disputed.
The objectives of this study were to develop an
empirical model of radiata pine root elongation and to
determine the relative importance of soil strength and soil
moisture content on root elongation, and further, to
quantify the parameters of a net-pressure mechanistic model
of root elongation for pine and to compare the values with
those observed for a more commonly studied crop (peas).
The empirical model showed seedling root elongation to
be three times more sensitive to increased soil strength
than to decreased soil moisture content. The observed
pattern of root behavior could be logically explained by a
concept of total external stress, where total external
stress was a summation of soil moisture potential and an
index of penetrometer resistance.
Measurement of pine root segment osmotic potential gave
values for cell threshold pressure (below which no
elongation takes place) and cell wall elasticity consistent
with values reported in the literature for other crops.
The response of pine and pea seedlings to moisture
stress in the absence of soil restraint was recorded.
Although root elongation of both species declined as
moisture potential decreased, pine seedlings showed no

osmotic adjustment to moisture potential and consequently
cell turgor decreased as root elongation declined. However,
for peas, turgor was maintained but the correlation between
turgor and elongation was poor, suggesting that the decline
in elongation was due to increased threshold pressure or
decreased cell wall elasticity.
Measurement of pea root potential, after seedling
growth in pots packed with soil of known penetrometer
resistance and moisture potential, showed 11% osmotic
adjustment to soil restraint and 41% adjustment to moisture
potential. The data was consistent with the empirical data
for radiata pine root elongation.
Root behavior, on growing into a more compact soil
layer, was consistent with a net-pressure model of root
elongation when studied in situ using a neutron radiography
technique. The technique was refined to allow a greater
number of exposures for a given reactor run.
Soil strength can be considered a general influence on
radiata pine root growth except where extremes of soil
moisture exist. Any increase in soil strength may reduce the
ability of the root to tolerate moisture stress. The general
influence of soil impedance on root growth and the slow
recovery of some soils after compaction, suggests a better
understanding of the likely effects of forest operations on
soil strength is needed if productivity losses following
harvesting are to be minimized.

Item Type: Thesis (Coursework Master)
Keywords: Pinus radiata, Plants, Effect of soil compaction on, Plants
Copyright Holders: The Author
Copyright Information:

Copyright 1987 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (M.Sc.)--University of Tasmania, 1988. Bibliography: p. 150-168

Date Deposited: 08 Dec 2014 23:58
Last Modified: 09 May 2016 06:07
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