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Predicting nitrogen deficiency in Eucalyptus nitens plantations using soil analysis and budgeting methods

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Moroni, Martin Thomas 1999 , 'Predicting nitrogen deficiency in Eucalyptus nitens plantations using soil analysis and budgeting methods', PhD thesis, University of Tasmania.

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Abstract

Areas of Eucalyptus nitens plantations in Tasmania are increasing and are expected to
enhance Australia's production of wood products. Standard silvicultural practises
involve N fertilisation of E. nitens plantations at planting and later ages, however not
all plantations respond to N fertiliser applied either at planting or at a later age. A
method to predict N fertiliser responses is required to prevent wastage and obtain
maximum productivity of Tasmanian E. nitens plantations. In this study nitrogen
budgeting and soil analysis methods were examined as predictors of the timing ofN
fertiliser responses.
Fourteen established research localities within Tasmania were used for the study,
covering a wide range of sites planted to E. nitens. Of the 14 sites, 11 were on basalt,
with single representatives on siltstone, granite, and alluvium. Rainfall ranged from
1039-1913 mm per annum and elevation ranged from 170 m to 650 m. Sites were
variously fertilised, some at planting, others at growth stages up to ten years.
Net nitrogen mineralisation (NNM) was estimated in situ at five sites encompassing
a wide range in N fertility. NNM in these sites ranged from 13 to 188 kg N ha-1 year-1.
Soil analyses for total N, total P, total C, hot KCl extractable N, soil solution and cold
KCl extractable N were examined as indices of NNM. Total N, total P, total C, and
hot KCl extractable N did not show large temporal variation and the values attributed
to these indicators separated the five sites into two groups, being sites with NNM
greater or less than 40 kg N ha-1 year-1. Sites of NNM >40 kg N ha-1 year-1 had total N
greater than 0.4%, total P greater than 0.2%, total C greater than 8% and hot KCl
extractable N greater than 100 µg N g soii-1. sites with lower NNM had concomitantly
lower values of these soil analyses.
The biomass of tree components was estimated from pre-determined regressions with
tree size. Measurements or estimates ofN concentrations led to estimates ofN content
in tree components at 14 sites. Nitrogen content oflitterfall was estimated at two sites
with high soil N analysis values, one of known high in situ NNM rates. Maximum
estimated N uptake in the combined above-ground biomass, the below-ground
biomass and the litterfall was 162 kg N ha-1 year-1.
Fertiliser responses were deemed to be significant (P<0.05) when increments in stem
diameter at breast height (1.3 m) over bark of fertilised trees was significantly greater
than diameter increments of unfertilised trees. For sites fertilised at planting the initial
year of significant response was recorded, while for sites fertilised at a later age (age
3-10 years) relative responses (diameter increment of fertilised trees I diameter
increment of unfertilised trees) were recorded. Of sites fertilised at planting, two had
responded by age two years, one by age three years and three had not responded by
age three years. Relative responses of sites fertilised at a later age ranged from 99% to
171%.
The formation of a simpler partial budget, where N supply was only in situ NNM (0
10 cm depth; 5 sites) and N demand was only the N increment into the above-ground
biomass, was always able to predict a significant response to fertiliser. However,
when NNM was estimated with soil analyses, fertiliser responses were accurately
predicted in only five of 14 sites.
The six sites fertilised from planting could be separated, on the basis of total soil N,
into those that responded [significant (P<0.05) increase in stem diameter at breast
height in N fertilised trees compared to unfertilised trees] before age three years (n=2),
at age three years (n=l) and after age three years (n=3) with total N of <0.28%, 0.28
0.51 % and >0.51 % respectively. All sites that responded to N fertiliser had soil
solution and cold KCl extractable nitrate below 0.1 mM and 1 µg N g-1 soil
respectively. The combination of total N and soil-solution or cold KCI-extractable
nitrate allowed prediction of N fertiliser responses at all of the 14 study sites.
Both soil analysis and one budgeting method were successful in predicting N fertiliser
responses of E. nitens plantations. The budgeting method was most successful when
NNM was estimated in situ, which together with the tree measurements required, is
labour- and time-intensive. Unless estimation of NNM and N uptake can be
simplified, the budgeting technique is unlikely to become part of standard
silvicultural practices.
A soil analysis method using total N and soil solution or cold KCl
extractable N is simpler and more likely to be used by forest managers.

Item Type: Thesis - PhD
Authors/Creators:Moroni, Martin Thomas
Keywords: Eucalyptus, Plants, Soils, Soils
Copyright Holders: The Author
Copyright Information:

Copyright 1999 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 (Ph.D.)--University of Tasmania, 2001. Includes bibliographical references

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