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Biochar as a soil amendment and productivity stimulus for Eucalyptus nitens plantations


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Wróbel-Tobiszewska, A (2014) Biochar as a soil amendment and productivity stimulus for Eucalyptus nitens plantations. PhD thesis, University of Tasmania.

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Biochar is a carbon-rich material produced by pyrolysis (heating in the absence of oxygen)
of biomass to capture combustible gases and generate heat and electricity. It can be added
to soils as a means to sequester carbon and to maintain or improve soil functions. The
physical and chemical properties of biochars determine their function as a tool for
environmental management. Soil changes and plant response have been analysed on
diverse soil types under various climatic conditions, water regimes, chemo-physical
environments and on different species. Yet, the exact mechanisms behind the effects of
biochar application are not fully understood and productivity gains vary greatly depending
on the type of biochar, application rates, crop species and environmental conditions.
Producing biochar from different organic waste materials appears to be a promising
method of achieving greater levels of certainty and flexibility for integrating carbon
sequestration, managing waste disposal costs and introducing a new solution into soil and
yield management in the conventional agricultural and forestry production systems.
Biochar, however, is not widely used by farmers or foresters in Australia, mainly due to the
lack of certainty concerning long-term consequences, yield gains and a lack of ‘know-how’
in the field of quality certification, transportation, logistics and cost efficiency.
Forestry is a significant industry in Tasmania, with large scale plantations of radiata pine
(Pinus radiata, D. Don) and Eucalyptus (E. globulus and E. nitens, H.Deane & Maiden) which
play an increasingly important role in supplying for national and international demand for
timber. Propagating robust seedlings for planting in the field is an important part of
plantation establishment as it influences potential yield, while also being a significant
budget component. As biochar has been reported to positively affect desirable soil
characteristics (e.g. increased nutrient efficiency, improved water holding capacity or
reduced bulk density) and enhance crop productivity, it was hypothesised that it can bring
benefits to Eucalyptus seedling growth.
The main objectives of this project were to investigate chemical changes of the soil, plant
material and soil solution following biochar application; and to determine the optimum
biochar dose required to positively influence eucalyptus growth under Tasmanian
conditions; both in a controlled nursery environment and during establishment in the field.
A secondary aim was to determine if commercial fertiliser rates could be reduced via biochar application to the growing medium. The final assumption was that biochar can be
profitably made from forest residues and utilized within the forest production systems of
The macadamia shell biochar used in this research was characterised as high in potassium
and sodium, relatively high in total carbon content and low in total nitrogen (N) and
phosphorus (P) content relative to other biochars described in literature. Two experiments
were conducted: a pot trial in which Eucalyptus seedlings were observed from sowing to 9
months; and a field experiment in the Florentine valley in South West Tasmania where
seedling establishment was monitored for 14 months. In both experiments the agronomic
characteristics of the seedlings and trees was monitored on a regular basis. Each
experiment had 4 sample collection periods when plant material and soil or potting mix
samples were collected and analysed. Percolating water was collected from custom-built
lysimeters installed in the field plantation.
Agronomic monitoring revealed that in both experiments fertiliser combined with certain
doses of biochar influenced the tree growth. The height of seedlings and young trees was
comparable between full fertiliser treatment (i.e. when no biochar was applied) and
treatments where medium biochar rates were combined with reduced fertiliser amounts.
However, biochar application did not result in significantly taller plants. Other agronomic
features were not influenced by biochar application in either experiment. The potting mix
was high in organic matter and the fertiliser applied at rates reflected industry standards.
While fertiliser rates were reduced to simulate a nutritionally poor soil, all other
environmental parameters were optimal in the pot trial. As previous reports have indicated
that biochar has more noticeable effects on poor quality soils, it is possible that the quality
of the potting mix masked the efficacy of biochar in relation to agronomic productivity,
although both soil and leachate parameters were influenced. In contrast, under field
conditions the biochar doses were applied at rates below that at which soil and leachate
parameters were modified in the potting experiment, thus the doses were possibly too low
to show a significant effect. The application method could also have influenced biochar
efficiency under field conditions.
Chemical and physical changes in the analysed mediums used implied a number of
different, in some cases contradictory, mechanisms. Biochar in both experiments increased
growing medium pH and released potassium and sodium to the soil. In the plant tissues, biochar induced changes, yet no clear trends were evident that macadamia biochar has any
sizable effect on the nutritional status of E. nitens in Tasmania. In most cases, the changes
in leaf tissue were correlated with changes in the soil with no evidence that biochar directly
influenced plant nutrient uptake.
Biochar did not have a clear effect on percolating water nutritional changes and the only
thing that can be concluded with certainty is that application of biochar increased
potassium infiltration from the soil. This is most likely connected with significant amount of
potassium introduced to the soil when biochar was applied.
While the mechanisms for the reported changes remain unclear, in many cases biochar was
responsible for changes in soil and plant material chemical characteristics and a limited
agronomic response. It appears that biochar is able to influence nutrients transformations
in the soil and therefore influence the soil environment for the E. nitens in Tasmania. It also
shows significant potential for reduced commercial fertiliser rates both in the forestry
plantations and in the forest nurseries.
The financial analysis was based on the trial outcomes and the local operating environment
in Tasmania; including current forestry procedures used for managing plantations in
Tasmania; and benefits resulting from biochar production and incorporation into
Tasmanian soils. The Biochar Scenario assumed on-site biochar making, out of post-harvest
forestry residues, and different methods of biochar utilization. The model was built in
Microsoft Excel® with help from Forestry Tasmania experts. A number of assumptions were
considered concerning: a) production costs, b) savings enjoyed by traditional operations
following biochar scenario implementation and c) biochar sale. The analysis revealed a
potential annual income of $179,514 resulting from introducing the Biochar Scenario on
270 ha. The sensitivity analysis identified the crucial factors responsible for scenario
profitability, namely biochar price and final product distribution.
The findings of this work supported the hypothesis that reducing common fertiliser rates
used for seedling establishment in forestry plantations is viable. It has also provided insight
into changes in both soil and plant tissue following macadamia shell biochar application to
Tasmanian soils. The financial analysis served as a solid background for the realistic
implementation of the Biochar Scenario for forestry industry in Tasmania.

Item Type: Thesis (PhD)
Keywords: biochar, forestry, soil, nutrition
Copyright Holders: The Author
Copyright Information:

Copyright 2014 the Author

Date Deposited: 03 Feb 2015 23:05
Last Modified: 15 Sep 2017 00:59
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