Potential changes

It is important to note that the assumptions used in this model were average from data available about plantations, management, growth response and local conditions in Florentine valley. The model is environmentally sensitive and the resulting cost and benefits values are expected to change in regards to micro-climate, soil type and other similar factors (Joseph, 2009).

Fertilising operations on forestry plantations in Tasmania are currently under transformation in order to utilize a new generation and better efficiency fertiliser type. The agronomic data used within this model was based on fertilising the plantations with standard di-ammonium phosphate (DiAP)(Chapter 4). It must be considered that the new fertiliser type is likely to interact with applied biochar unlike DiAP and result in significantly different final outcome (trees height, nutrient efficiency from fertiliser). A pilot experimental trial would be required to estimate expected results of new type of fertiliser in combination with biochar.

Equally, the topic of increasing nutrients release from biochar would be interesting to investigate. Certain organic additives (i.e. chicken litter, farm animals manure) have been shown to increase biochar ability to introduce nutrients to the soil (Sarkhot et al., 2012). An opportunity to collect animal manure and litter from local farms and its addition to woody feedstock during the pyrolysis process might decrease fertiliser rates required for the plantations and could be used on a wider scale as a nutrient-application method in the future. In northern Tasmania there is a large scale dairy industry which could provide interesting possibilities for making biochar enriched by animal manure.

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Tasmania has been presented as an Australian state with a significant potential to use forest residues for generating bio-energy and bio-products (Greaves and May, 2012; Rothe. A, 2013). With the current production of 300,000 m3 _{(Wood et al., 2009) of eucalypt sawlog} and other forestry-related industries the potential arising from primary and secondary forests products and residues cannot be overestimated. Biomass estimating reports however, are based on woody residues used mainly for energy generation purposes while biochar has been discussed very briefly in proposed solutions. Co-operating with other authors and working on the basis of already existing biomass reports but introducing biochar scenario on a wider scale could provide interesting solutions for proceeding woody residues under Tasmanian conditions.

8.8.

Conclusions

The evaluation of this model shows that biochar production from forest residues may be feasible dependent on receiving a minimum of $400 per tonne when 30% of the produced char is sold into a commercial market. The proposed operation was most sensitive to the market biochar price and the amount of biochar dedicated to enter the market, which are both considered highly changeable in the developing Australian biochar market. Model assumptions included only one source of residues, namely plantation post-harvest residue wood while other sources of biochar feedstock (i.e. thinnings and native forest woody residues) could enlarge the scale of biochar scenario incorporation, if considered in the analysis. Similarly, the opportunities connected with pyrolysis gasses production were not considered in the model due to the type of pyrolyser used. Other unaccounted benefits include community advantages resulting from creating new jobs or environmental benefits like decreased fire risk or on-site burns smoke management. The results of this scenario would be best confirmed by a practical biochar production and utilisation system based in Tasmania.

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9.FINAL DISCUSSION AND CONCLUSIONS

9.1.

Introduction

The objectives of this research were to test the agronomic and financial feasibility of biochar application to Tasmanian soils and forestry plantations. Two experiments (pot and field experiments) were established and monitored in order to gather data to support hypotheses that macadamia biochar can bring beneficial effects to soil quality, plant nutrition and agronomic response in E. nitens seedlings as well as allow decreasing common fertiliser rates used in forestry plantations (Chapter 1). Results from the experimental analyses were incorporated into the financial model, along with market assumptions and local economic and environmental suppositions, to investigate financial feasibility of producing and incorporating biochar on Tasmanian-based forestry plantations. The results have shown initially increased availability of potassium, sodium, nitrate-N and phosphorus; elevated pH in the potting mix and higher concentration of sodium and potassium in the field plantation soil (Chapter 5), though over time the effect was diminished. The leaf tissue concentration in response to biochar in both experiments revealed P, K and Na increase in the pot trial and in some, although not all cases, some clear trends were evident (Chapter 7). Biochar application in the field increased potassium leachate which was attributed to higher K availability in soil following biochar application (Chapter 6). Char application did not result in significantly taller trees or greater biomass production in general, but two biochar application rates combined with halved fertilisation resulted in seedlings of similar quality (height) to the ones produced under full fertiliser rate with no biochar applied (Chapter 7). These results indicated a potential of decreasing fertiliser rates commercially used in forestry plantations in Tasmania if supported by further research.

The financial model based on the idea of on-site biochar production from the post-harvest residues revealed a potential annual income of nearly $180,000 based on processing post- harvest residues from 270 ha (Chapter 8). The sensitivity analysis showed that a critical factor for model financial feasibility is biochar market demand and price, which is presently unstable in the developing biochar market in Australia.

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9.2.

Agronomic and chemical changes

9.2.1.Soil

While in some cases the trends in nutrients levels were consistent with existing theory and explicable (Colwell potassium, pH, and exchangeable sodium, magnesium, aluminium and calcium), some of the nutrient dynamics could not be clearly related to any particular known mechanism.

Some changes in the soil were less noticeable than anticipated. Macadamia biochar did not have an effect on soil electrical conductivity or pH under field conditions. The EC in the potting mix was lowered by biochar application, which was concluded to be an effect of cation adsorption from the soil solution to biochar surfaces. Some evidence of accelerated nitrification in the PM and increased potassium content in the field soil suggested that macadamia biochar influenced both the direct release of nutrients and affected nutrient transformation mechanisms (Chapter 5). The high SSA of macadamia biochar (Chapter 3) was suspected to influence soil microbial activity and result in readily noticeable changes in bacteria- related nutrient levels (mainly N and P), especially in the field experiment. Stimulated microbial activity could have been a case in this experiment, however, as it was not analysed and there were few changes in soil that would allow any conclusion about its potential importance, this aspect must remain unresolved and possibly be the subject of further research.

Biochar influence was much more evident in the pot experiment in comparison to the field trial changes. This is most likely the effect of the comparatively low biochar rates used in the field study. The highest biochar rate applied in the glasshouse equalled 100 t ha-1 _while in the field the maximum dose was equivalent to 20 t ha-1_{. Most of the PM changes in the} controlled environment were reported for high biochar rates (50-100 t ha-1_{) which provides} a potential explanation that low char rates applied in the field were responsible for the lack of substantial effects of biochar.

The positive influence of biochar on soil condition and plant growth is sometimes related to the effect of biochar aging in soil (Nguyen et al. 2009, Atkinson et al. 2010). As biochar ages, its overall chemical and physical characteristics change, including surface charges and bulk density and others (Chapter 2). It is possible that the duration of both pot and field experiments were too short to reveal the differences resulting from long-term biochar

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induced changes in soil. However, the extractable nutrient concentrations decline to close to initial values in around 1 year suggests that there are likely to be limited long term effects. Despite this, a longer-term study with higher rates of biochar application would help to understand changes to soil nutrient availability and transformation mechanisms as a result of biochar application.

Although biochar induced changes were the most noticeable in the potting mix the full extent of potential transformations in growing media may have been mitigated by this mix’s inherent properties. The PM used in the experiment contained a large proportion of organic matter (Chapter 4) and might have masked the effects of biochar application. For instance, the high proportion of peat in the potting mix would have imbued an already substantial CEC capacity before the char was added. This observation might be extended to hypothesis that biochar may be used in the commercial potting mix for growing Eucalypt seedlings and replace, to some extent, pine bark or other high organic matter components of growing mixes. Further research would however be required to formulate firm recommendations.