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The use of N:S ratios as a means of diagnosing S deficiency in a number of pasture species.


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Martinick, Wolf-Gerhard 1975 , 'The use of N:S ratios as a means of diagnosing S deficiency in a number of pasture species.', PhD thesis, University of Tasmania.

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The subject was introduced by a review of N and S uptake and
plant fractions, and concepts for diagnosing nutrient requirements.
The relationship between total and alcohol insoluble plant
N:S ratios ((N:S)t and (N:S)p) and yield was initially studied in pot
and field experiments with oats, and subsequently extended to pot
experiments with perennial ryegrass, foggrass, rape and white and subterranean
clover, and to pasture trials.
In all species severe N and S imbalances substantially affected
the respective (N:S)p 's, but with the exception of rape, (N:S) p's were
markedly less affected than corresponding (N:S)t's, and if extreme N
and S imbalances are excluded from consideration, then the respective
(N:S)p's were either constant, or their variability was such that they
were arbitrarily referred to as tending towards constancy. These
"constant" values varied between species (about 15 in subterranean and
white clover, and about 11 to 13 in oats, foggrass and ryegrass), and
with physiological development, the effects of physiological development
appearing to be more pronounced in relatively young than in old plants.
This sensitivity of (N:S)p was considered to be due to (a) analytical
methods of determining Np and Sp, (b) the composition of the protein
fraction, (c) the severity of N and S imbalance, and (d) differences in
physiological age.
In both the gramineous and clover species, severe S stress was
always accompanied by (N:S) t 's substantially exceeding the respective
constant values to which their (N:S)p 's tended, whilst in corresponding
S sufficient plants, (N:S) t's were usually equal to, or less than
corresponding "constant" (N:S)p ranges. This latter group frequently
included low N-low S treated plants, suggesting that in these plants
the internal S status was in balance with the internal N status. A
progressive increase in (N:S) t's above their corresponding "constant"
(N:S)p 's tended to be associated with increasing S stress, but it was
difficult to establish when this increase became physiologically critical.
The investigations with gramineous plants were restricted to
total foliage analysis. In clovers the S status was best reflected in
laminae-only samples, but for diagnostic purposes, a precise separation
of laminae from petioles was not necessary.
Unlike pot experiments, where the S status of grass-clover
swards could be diagnosed by (N:S) t 's in any of the species, in pasture
situations, only (N:S) t changes in clover components were sufficiently
substantial for meaningful diagnosis. This was demonstrated in a field
experiment in which management and S treatments were varied.
Results of 19 simple grazing trials emphasise that the diagnosis
assesses the S status (in relation to N status) as at the time of sampling,
and is not a reliable guide to future requirements, and that the
time of year is critical for meaningful sampling.

Item Type: Thesis - PhD
Authors/Creators:Martinick, Wolf-Gerhard
Keywords: Pastures, Soils
Copyright Holders: The Author
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Copyright 1975 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
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Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1976. Includes bibliographies

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