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Item Dynamic environmental payback of concrete due to carbonation over centuries(Elsevier B.V., 2024-09-30) Elliot T; Kouchaki-Penchah H; Brial V; Levasseur A; McLaren SJThis research introduces a dynamic life cycle assessment (LCA) based carbonation impact calculator designed to enhance the environmental evaluation of cement-based construction products. The research emphasizes the limitations of static LCAs which fail to capture the time-dependent nature of carbon sequestration by carbonation. We provide an easy-to-use spreadsheet-based LCA carbonation model. The model is available in the supplementary information, and includes a suite of changeable parameters for exploring the effect of alternative environmental conditions and concrete block composition on carbonation. The tool enables use of both a static and dynamic LCA method to calculate the production emissions and carbonation sequestration of a concrete block over a 1000-year time horizon. Carbonation can partially mitigate initial production emissions and adjust radiative forcing over long periods. Using a static attributional LCA approach, carbonation sequesters 6 % of the CO2 generated from its production emissions. We describe the ratio of carbonation to production emissions as the partial “carbonation payback”, and with dynamic LCA show the variation of this ratio over time. Considering time by applying the dynamic LCA approach, we find this partial “carbonation payback” is split between uptake during the 60-year service life (0.13 kg CO2) and the 940-year end of life period (0.12 kg CO2) in our baseline case. Further scenario analyses illustrate the significant variability in carbonation payback, driven by environmental factors, cement composition, and the use of supplementary cementitious materials. The results highlight the critical role of modelling choices in estimating the carbonation payback. The carbonation calculator developed in this study offers a sophisticated yet user-friendly tool, providing both researchers and practitioners with the ability to dynamically model the sequestration potential of concrete, thereby promoting more sustainable construction practices.Item The long-term effects of elevated CO₂ on soil organic carbon sequestration, partitioning and persistence in a grazed pasture : a thesis presented in partial fulfilment of the requirements for the degree of Doctor in Philosophy in Soil Science at Massey University, Manawatu, New Zealand(Massey University, 2024-03-04) Gonzalez Moreno, Marcela AngelicaThe increased concentration of atmospheric carbon dioxide (CO₂) is a significant driver for climate change and also influences the cycling of soil organic carbon (OC) in ecosystems. Despite the importance of grassland soils as a sink for CO₂, the effect of long-term exposure to elevated CO₂ (eCO₂) on OC sequestration, partitioning and persistence in grazed grassland soils is poorly understood. This thesis aimed to investigate the effect of eCO₂ on soil OC stocks, the partitioning of OC in soil fractions and persistence in a grazed legume-based pasture at the New Zealand (NZ) Free Air CO₂ Enrichment (FACE) facility. The NZ-FACE, established in 1997, is the only FACE experiment worldwide that includes the influence of grazing practices on the above- and below-ground components of the OC cycle. The effect of eCO₂ on soil OC persistence and stability was assessed by measuring changes in soil OC stock, in the distribution of soil OC in the soil fractions by wet fractionation analysis and in the soil OC decomposition pathways by determining the molecular composition of soil organic matter (OM) by pyrolysis analysis followed by gas chromatography/mass spectroscopy (GC-MS) and thermally assisted hydrolysis methylation-GC-MS (THM-GC-MS) analysis to a soil depth of 250 mm. In Chapter 3, we assessed OC storage and persistence in the soil fractions in a grazed legume- based pasture exposed to eCO₂ for 22 years on Pukepuke soil (Mollic Psammaquent) at three soil depths. Our study revealed that after 22 years of exposure to eCO₂ there were no significant changes in the stocks of OC and N as well as the partitioning of OC within different soil fractions in the Pukepuke soil. Interestingly, in the last 10 years at the NZ-FACE facility, there has been a sharp reduction of OC and N stocks in the Pukepuke soil, independent of the CO₂ treatment. We suggest that in the sandy Pukepuke soil under conditions of warmer temperatures and a wetter system, the deficiency that has emerged in soil nutrient availability, the environmentally enhanced plant growth and the larger amounts of fresh OM input has caused a positive priming effect, mainly in the labile fraction. Even though eCO₂ did not change the soil OC stocks nor OC content in the soil fractions in any soil layer, it did modify the soil nutrient status (phosphate in particular) and did increase polysaccharides and aliphatic proportions in the coarse particulate organic matter and micro-aggregates indicating that the priming was further enhanced in eCO₂ soils with this effect being especially prominent in the 50 – 150 mm soil layer (Chapter 3). In Chapter 4, the hypothesis that grazing animals, by returning nutrients in urine, dung, and plant litter trampled into the soil surface, would contribute to an increase in soil OC and N stocks under eCO₂ was investigated and rejected. Despite not finding any interaction effect between eCO₂ and defoliation treatment on the soil OC stocks and partitioning in the soil fractions, the presence of an interaction effect in the soil OM molecular composition suggests that distinctly different OC decomposition pathways exist depending on pastures management under eCO₂. Our study showed that under grazing there was an accumulation of lignin-derived OM, which reveals a higher proportion of shoot-derived rather than root- derived OC under eCO₂. In Chapter 5, the influence of the inherent properties of a soil – which might enhance or limit the effects of eCO₂ on soil OC persistence and stability – was examined in two contrasting soils (Pukepuke and Stratford; a Entic Dystrandept) in mesocosms installed at the NZ-FACE in May 2005 and extracted after 15 years. Our results showed that over the course of the mesocosm study, OC and N contents and stocks (to 150 mm soil depth) in the Pukepuke soil declined by 16 t ha-1 under ambient CO₂ atmosphere, possibly as a result of soil disturbance during the establishment of the mesocosms. In the Stratford soil, with the ability to strongly preserve OM through mineral associations, the decline in soil OC was much smaller (5 t ha-1). Elevated CO₂ interacted with soil type and after 15 years of exposure to eCO₂, the Pukepuke soil had 6.5 t ha-1 more OC stocks, compared to the same soil under ambient CO₂ conditions, while no differences were found in the OC stocks of the Stratford soil (Chapter 4). These findings indicate that in the Pukepuke soil the eCO₂ treatment might have (i) helped overcome the impact of disturbance by favouring plant growth and generating a larger plant detritus input to the soil that enabled the partial replenishment of the OC loss at the time of mesocosm establishment, or (ii) limited the impact of disturbance, as eCO₂ often improves soil aggregation. It is crucial to consider that (i) the Stratford soil was subjected to ~50% less precipitation at the NZ-FACE compared to its original location and (ii) the mesocosm might have introduced new variables due to physical barriers. Thus, extrapolating the findings to field conditions at the NZ-FACE facility and elsewhere requires cautious interpretation. The findings presented in this thesis contribute significantly to enhancing our understanding of the mechanistic processes underlying the influence of eCO₂ on the stabilization and mineralization of soil OM. These insights have direct implications for the development of sustainable agricultural management practices in response to a changing environment.Item An investigation of pasture legume root and shoot properties that influence their rate of decomposition in soil : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Palmerston North, New Zealand(Massey University, 2021) Walker, HelenAgriculture is the largest source of GHG emissions (47.8 %) in New Zealand. Emissions are increasing annually, driven by increasing relative productivity. Irrespective of the climate regime, grassland soils have historically sequestered large amounts of atmospheric C into SOM (soil C) raising interest in the potential for agricultural emissions to be mitigated through acceleration of soil C sequestration. Soil C sequestration is a direct result of the rate of deposition (excreta, plant litter, and roots) exceeding the rate of decomposition and can be raised by: 1) increasing the rate of input (manipulating the drivers of vegetation); or 2) increasing the longevity of C in the system. This PhD study tests the hypothesis that C sequestration in pasture soils can be accelerated, by selecting pasture species that contribute slower decomposing litter to soil. A series of laboratory incubation studies were conducted to measure the decomposition rate (CO₂ emissions) of plant shoots and roots with high (Lotus pedunculatus) and low (Trifolium repens) tannin contents. In addition the effects of residue management (fresh and freeze dried), application to soil (fresh - surface, freeze dried - surface, and freeze dried - mixed) and rate of application (2, 5, 10 mg C. g⁻¹ soil) were evaluated. The effect of species, plant management, plant part, and rate of application on C emissions were all statistically significant (P < 0.05), with large variance in CO₂ emissions associated with all treatments. Plant species and plant part influenced the amount of C retained in the soil, although not entirely as expected. Lotus pedunculatus shoot material retained significantly more C than Trifolium repens shoot material at all rates of application (2, 5, 10 mg C. g⁻¹ soil); whereas Trifolium repens root material retained significantly more C than Lotus pedunculatus root material at all rates of application (P < 0.05). Notably plant roots and particularly Trifolium repens roots had slow decomposition rates compared to shoot materials. Research showed that soil and plant residue preparation greatly influenced the total amount of C retained for both shoot and root treatments, with more C retained under conventional incubation techniques (dried - mixed application) than with fresh applications. This indicates that CO₂-C retention in a field situation may be overestimated if predicted using conventional laboratory incubation techniques. However from a research perspective it is infinitely easier to work with pre-dried incubation materials (timing, handling, chemical analysis) so it is highly likely that this style of incubation practice will continue to be the preferred method of research. Care must therefore be taken when extrapolating the results from such incubation studies. A four compartment (2 soil C pools, persistent and labile; and 2 plant C residue pools, fast and slow) computer simulation model was developed and provided an excellent explanation of the CO₂ emissions from the incubation of fresh shoot and root material. The measurement of the metabolisable energy (ME) or lignin contents of plant shoot and root were successful in parameterising (allocating C to) the fast and slow plant residue pools. Plant tannin content was not able to explain CO₂ emission rates. The experimental and modelling studies provide evidence that grazed pasture rotations in mixed farming systems could be manipulated, by careful plant pasture species selection, to accelerate soil C sequestration. Litter and root metabolisable energy (ME) or lignin contents could be useful in species selection, but further research into other pasture species and pasture management techniques is required. Field studies should focus on the role of clover (Trifolium repens) roots in building pasture soil C content.Item Guidelines for small scale biochar production system to optimise carbon sequestration outcome : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Bioprocessing Engineering at Massey University, Palmerston North, New Zealand(Massey University, 2019) Cortez Pires de Campos, ArthurBiochar is made in a 60 kg batch pyrolysis reactor developed by Massey University in both prior work and during this project. This thesis details the design and control features necessary to produce biochar (charcoal) at temperatures ranging from 400-700°C. It also examines the emissions abatement necessary to achieve the best possible carbon footprint by combusting the gases to avoid release to the atmosphere. The feedstock for this work was Pinus radiata without bark. The biochar reactor is a vertical drum mounted on top of a combustion chamber containing two forced draft LPG burners. The combustion gases pass through an outer annular drum and so heat the biomass through the external wall. Evolving pyrolysis gases then move toward a central perforated core inside the drum, then descend into the combustion chamber where they are partially combusted. The range of highest treatment temperatures (400-700°C) was extended by controlling the partial combustion by varying a secondary air supply into the combustion chamber (previously only 700°C was achievable). Effective emissions abatement requires complete combustion. This work reveals that the flammability of the pyrolysis gases is not high enough to self-combust and so does not remove soot and other products of incomplete combustion, such as CO and CH4. Therefore, supplementary fuel is always needed. Here, this was achieved using modulated LPG burners at the flare. This system has the problem of batch pyrolysis reactors, where the release of volatiles from the reactor is uncontrolled, making the design of a variable rate flare system a non-trivial matter. Modifications made to the reactor design in this project include insulating the flare chimney, extending it to provide sufficient residence time, and installing adjustable vents to ensure sufficient air entrainment for complete combustion. This achieved emissions of CO and CxHy (hydrocarbon, mostly CH4) of 32 and 51 ppm respectively, which were well within the US EPA limits for both suspension and fluidised bed biomass burners(2.400 and 240 ppm respectively). The net environmental impact was determined for char made at 700°C, through carbon footprint analysis. An efficient system is needed to achieve a net sequestration benefit. Here, even with emissions abatement and the above mentioned very low CO and CxHy emissions, no net benefit was achieved. With the flare working, the net fractional sequestration was -0,14 (kg C sequestered)/(kg C in biomass). Then, when the flare is turned OFF, the net fractional sequestration was -1,2401 (kg C sequestered)/(kg C in biomass). Therefore, another frame of reference for well-operated systems is that the permissible emission should be less than 0.001 (kg C emitted as CO)/(kg C biomass), without considering methane or other GHGs.Item Are low-producing plants sequestering carbon at a geater rate than high-producing plants? : a test within the genus Chionochloa : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University, Palmerston North, New Zealand(Massey University, 2016) Dickson, Matthew Phillip SijbePlant life and primary production play an important role in the global carbon (C) cycle through the fixing of atmospheric C into the terrestrial biosphere. However, the sequestration of C into the soil not only depends on the rate of plant productivity, but also on the rate of litter decomposition. The triangular relationship between climate, litter quality, and litter decomposition suggests that whilst low-producing plants fix C at a slower rate than high producing plants, they may release C at an even slower rate, due to the production of a recalcitrant litter. Here, the relationships between environment, productivity, litter quality and decomposition are investigated to determine their relative influences on C sequestration for taxa in the genus Chionochloa. Annual productivity was measured in situ for 23 taxa located across New Zealand, whilst litter and soil were collected for analyses and two ex-situ decomposition experiments; litter incubation on a common alpine soil, and litter incubation on each taxon's home-site soil. Plant growth rate was found to be positively correlated with both litter nitrogen and litter fibre content. Litter decomposition on the common soil was instead negatively correlated with lignin content, which showed a strong correlation with phylogeny, as opposed to environment or growth rate. When incubated on home-site soils, litter quality had no influence on decomposition, which was instead positively correlated with the rate of soil C decomposition, and negatively correlated with both soil organic matter and soil water content. On the common soil there were weak correlations between productivity and decomposition; however the proportional increase in productivity was greater than the corresponding increase in decomposition, resulting in high-producing plants sequestering C at a greater rate than low-producing plants. However, there was no correlation between productivity and decomposition on the home-site soil, with soil water content being a better predictor of C sequestration rate than productivity. Despite the range of variation in morphology, ecophysiology, productivity and habitat displayed within the Chionochloa genus, taxa all produced litter of a very similar quality. Breakdown of that litter is then most strongly influenced by the environment in which decomposition occurs, as opposed to the quality of the litter. Any subsequent differences in rates of C sequestration are therefore most influenced by the environment decomposition occurs in, with wet and cool environments likely to result in increased rates of C sequestration, independent of the rate of productivity.Item Investigation on the effect of biochar addition and the use of pasture species with different rooting systems on soil fertility and carbon storage : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy (MPhil) in Soil Science at the Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand(Massey University, 2015) Wisnubroto, Erwin IsmuThere is a potential to increase soil carbon (C) sequestration in New Zealand pastoral soils, especially in the subsoils where the soil C stocks have been reported to have a greater C saturation deficit than the topsoils. Selecting pasture species with deeper root systems will enhance soil formation at depth and mineral weathering, thus enhancing the potential for soils to stabilize organic matter (OM). Moreover, the addition of biochar may increase the stable C pool of soils and provide other additional benefits. Up to the present time few studies have investigated the potential of biochar to promote root growth and allocation of plant C to the subsoil. A glasshouse study was carried out to examine the effect of adding a nutrient-rich biochar at various dose (0, 1.5, 5 and 10 Mg ha–1 without nitrogen (N) fertiliser; 0, 1.5, 10 and 20 Mg ha–1 with N fertiliser at a dose of 113 kg N ha–1) to a sandy soil on plant growth (aboveand below-ground). The results indicated that, in the absence of N limiting conditions, biosolids-derived biochar could improve plant biomass yield as a result of the addition of available P and K. This amendment also caused an increase in plant root length. Subsequently, a 2-year lysimeter trial was set up to compare changes in C stocks of soils under deep- or shallow-growing pastures as well as to investigate whether biochar addition below the top 10 cm could promote root growth at depth. For this: i) soil ploughing at cultivation for pasture establishment was simulated in two different soils (a silt loam soil and a sandy soil) by inverting the 0–10 and 10–20 cm depth soil layers, and biochar was mixed at a rate of 10 Mg ha–1 in the buried soil layer, where appropriate; and ii) three pasture types with contrasting root systems were grown. Distinctive biochars were selected for these two soils so that soilspecific plant growth limitations could be overcome. In the silt loam, soil inversion resulted in a net loss of native organic C in the buried horizon under shallow-rooted species, but not under deep-rooted species. The addition of a C-rich pine biochar (equivalent to 7.6 Mg C ha–1) to this soil resulted in a net C gain (6–16% over the non-biochar treatment, calculated up to 30 cm; P < 0.05) in the buried soil layer under all pasture treatments; this overcame the net loss of native organic C in this horizon under shallow-rooted pastures. In the sandy soil all pasture species were able to maintain soil C stocks at 10–20 cm depth over time. In this soil, the exposure of a skeletal and nutrient-depleted soil layer at the surface may have fostered root growth at depth. The addition of a nutrient-rich biosolids biochar (equivalent to 3.6 Mg C ha–1) to this soil had no apparent effect on total C stocks. In this 2-year study, none of the biochar amendments affected either pasture yield or root growth. More research is needed to understand the mechanisms through which soil C stocks at depth are preserved.Item Productivity, decomposition and carbon sequestration of Chionochloa species across altitudinal gradients in montane tussock grasslands of New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatū, New Zealand(Massey University, 2015) Krna, Matthew AaronAnthropogenic activities are drastically altering Earth’s terrestrial, aquatic and atmospheric processes and altering carbon (C) and nutrient cycling. Carbon sequestration, which can be negative feedback to climate change, may help mitigate humanity's impacts on Earth’s climate. Carbon sequestration is a natural process occuring when the fixation of C is greater than the release of C back to the atmosphere from a specified system over an annual timeframe, minimally. Investigation of annual plant productivity, decomposition and alterations in relationships between productivity and decomposition across altitudinal and climate gradients will provide insight into C sequestration driven by environmental and plastic responses of species to climate change. This research investigates how alterations in climate influence ecoclinal populations of Chionochloa species’ in terms of their productivity, decomposition, as well as C and nutrients, across altitudinal gradients on Mounts Tongariro and Mangaweka, Central North Island, New Zealand. Further, impacts on the C sequestration are investigated through alterations in productivity to decomposition ratios (P:D). Reciprocal translocations of living Chionochloa plants and litter decomposition bags were performed across plots every 100m in elevation (equivalent to 0.6oC mean annual lapse rate). Trends were analysed based on experimental plots of origin and destination, and were compared with in situ plants and home site transplants. Productivity of downslope transplants increased at lower elevation plots (i.e. in warmer climates). Leaf litter experienced greater mass loss based on litter translocation to higher elevations on Mount Tongariro and at lower elevations on Mount Mangaweka likely owing to precipitation and temperature gradients respectively. The chemical and constituent composition of leaves and decomposed litter following translocation indicates strong environmental effects on both the plastic responses of plants in growth and the alterations in mass loss from decomposition. Despite chemical and constituent differences in Chionochloa species’ tissues and decomposed litter across gradients, the P:D ratios were greater in warmer environments of lower altitudinal plots. The increased productivity observed outweighs the less-climatically responsive decomposition, indicating greater C sequestration in New Zealand’s tussock grasslands is likely to occur with warming associated with climate change, providing an environmental and economic imperative for conservation of these indigenous grassland systems.Item Biochar systems for carbon finance -- an evaluation based on Life Cycle Assessment studies in New Zealand : a thesis presented in partial fulfilment of the requirements of Doctor of Philosophy in Science at Massey University, Wellington, New Zealand(Massey University, 2013) Anaya de la Rosa, Ruy KorschaChar produced from the pyrolysis of biomass and applied into soils (biochar) can, under some conditions, improve soil functions and sequester carbon (C) over millennia. In New Zealand, if 80% of the available biomass residues were converted into biochar, about 1.7 Mt CO2 could be sequestered annually. This represents ~2.4% of NZ’s total annual greenhouse gas (GHG) emissions. However, the trade-offs associated with alternative uses of biomass need to be assessed from a life cycle perspective, particularly when considering policymaking. The biomass feedstocks evaluated using Life Cycle Assessment were orchard prunings, logging residues, and wheat straw. The goals were i) to compare alternative management scenarios and ii) to determine the use of biomass that can achieve the largest amount of carbon credits in order to support policymaking. The biomass for heat-only (HO) scenario could mitigate 276 – 1,064 kg CO2-eq per t biomass; the combined heat and power (CHP) scenario could reduce 410 – 1,608 kg CO2-eq per t biomass; and the biochar scenario could abate 271 – 792 kg CO2-eq per t biomass. Ranges vary according to the type of feedstock assessed and the type of fossil fuel (coal or natural gas) displaced. The assessment of the HO and CHP systems giving greater GHG emission reductions than the biochar system can be misleading as these only involve fossil-fuel offsetting whereas the biochar system would sequester some carbon irrespective of the other activities assumed to be displaced. The biochar carbon stability factor is the key component that affects its capacity to mitigate climate change. A distinctive C accounting, reporting and crediting approach should be developed for biochar to have high economic potential in carbon-pricing mechanisms. Several approaches for incentivising biochar carbon sequestration were explored. These include using conservative carbon-accounting estimates, issuing temporary credits, establishing buffer funds, creating carbon credit multipliers, and inventing a new unit such as ppm CO2 reductions for recognising atmospheric CO2 removals as opposed to avoiding GHG emissions. While biochar technology is currently facing numerous barriers for acceptance in carbon markets, its future is promising since biochar production also offers potential in the agriculture, energy and waste management sectors.Item Development of methodologies for the characterisation of biochars produced from human and animal wastes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science, Institute of Agriculture and Environment, College of Sciences, Massey University, Palmerston North, New Zealand(Massey University, 2013) Wang, TaoBiochar is charcoal made from waste biomass and intended to be added to soil to improve soil function and reduce emissions from the biomass caused by natural degradation to CO2. Biochar technology has many environmental benefits, such as carbon (C) sequestration, waste management, soil improvement and energy production. High quality biosolids (e.g., low in heavy metals) and animal wastes represent an adequate feedstock for production of biochars. Wide variation in biochar properties, dependent on feedstocks, process conditions and post-treatments, lead to large uncertainties in predicting the effects of biochar application on the surrounding ecology, and the productivity of particular crops under specific pedoclimatic conditions. It is essential to well-characterise biochars prior to its incorporation into soils. Therefore, the aims of this thesis were (i) to investigate the C stability and nitrogen (N) and phosphorus (P) availability in biochars produced from municipal and animal organic wastes at different pyrolysis temperatures; and (ii) to develop simple and robust methods for characterisation of C stability and nutrient availability in biochars. Two types of feedstock, (i) a mixture (1:1 dry wt. basis ratio) of alum-treated biosolids (from anaerobic digestion of sewage, ~5% dry wt. of Al) and eucalyptus wood chips (BSe), and (ii) a mixture (1:1 dry wt. basis ratio) of cattle manure (from a dairy farm) and eucalyptus wood chips (MAe), were used to produce biochars at four different pyrolysis temperatures (highest heating temperature: 250, 350, 450, and 550°C). The stability of C in charred materials increased as pyrolysis temperature increased, as proved by the increase of aromaticity and the decrease of atomic H to organic C (H/Corg) ratio, volatiles to (volatiles + fixed C) ratio, C mineralisation rate and % K2Cr2O7 oxidisable C. According to the IBI Guidelines (IBI 2012), an upper H/Corg ratio limit of 0.7 is used to distinguish biochar samples from other carbonaceous biomass based on the consideration of C stability. According to this classification system, MAe-450 and MAe-550 biochars complied with this specific C stability requirement; this was also the case of BSe-450 and BSe-550 when their H values were corrected to eliminate the contribution of inorganic H from Al oxy-hydroxides. Both organic H (Horg) and Corg forms were used in the calculation of this index instead of their total amounts, as the latter would also include their inorganic C or H forms – which can represent a considerable amount of C or H in ash-rich biochars – and these do not form part of the aromatic structure. Therefore, various methods, including titration, thermogravimetric analysis (TGA), acid fumigation and acid treatment with separation by filtration, were compared to quantify the carbonate-C in biochars. Overall, the titration approach gave the most reliable results as tested by using a CaCO3 standard (average recovery>96% with a relative experimental error <10% of carbonate-C). To assist in the prediction of the mean residence time (MRT) of biochar C in soils, simple models, based on their elemental composition and fixed C content, were established to calculate C aromaticity of biochars. This was able to replace methods using more costly solid state 13C NMR spectroscopy. Biochar samples produced from MAe and BSe feedstocks were hydrolysed with a 6 M HCl to extract labile N (hydrolysable), which was considered the fraction of N that would be available in short term; and with 0.167 M K2Cr2O7 acid solution (dichromate) to determine potentially available N in the long term. An incubation study of biochars mixed with acid washed sand was also conducted at 32 °C for 81 d to study short-term N turnover pattern. Results showed that fractionation of biochar N into ammonia N (AN), amino acid N (AAN), amino sugar N (ASN), and uncharacterisable hydrolysable N (UHN) revealed the progressive structural rearrangement of N with pyrolysis temperature. Hydrolysable- and dichromate oxidisable-N decreased as pyrolysis temperature increased from 250 to 550 °C, suggesting N in biochar becomes more stable as pyrolysis temperature increased. Organic N was an integral part of the biochar structure, and the availability of this N also depended on the stability of biochar C. The ratio of volatile C (representing labile C) to total hydrolysable N (THN) was proposed as a useful indicator of whether net N mineralisation or immobilisation of N in biochar occurred. Phosphorus in feedstock was fully recovered and enriched in the biochars under study. Various methodologies were employed to investigate the bioavailability of P in biochars, including (i) a bioassay test using rye-grass grown in a sandy soil fertilised with biochars; (ii) soluble P extractions (resin extraction and Olsen extraction) from biochar amended soils; and (iii) successive resin P extractions of soils treated with biochars. The results obtained with the different methods confirmed that P bioavailability diminished following the order of dihydrogen phosphate (CaP) > MAe biochars> BSe biochars > Sechura phosphate rocks (SPR). Plant availability of P in biochars could be predicted from the amount of P extracted in 2% formic acid extractable P (FA-P). In addition, resin-P was considered as a useful test for characterising P bioavailability in soils fertilised with P-rich biochars. However, more investigations with a wider range of soils and biochars are needed to confirm this. Pyrolysis temperature played a minor role on P availability in biochars produced below 450°C compared to the influence of the type of feedstock. This was supported by the results on (i) plant P uptake, (ii) 2% formic acid extraction, and (iii) successive resin P extractions. The availability of P in biochars produced at 550°C decreased noticeably compared with that in lower temperature biochars. The Hedley P fractionation procedure was also carried out to examine the forms and transformation of P in biochar after its application into soils under the influence of plant growth. Generally, biochar P contributed to the readily available resin-P and moderately available NaOH-Pi fractions, and some equilibrium likely existed between these two fractions, both of which provided P for plant uptake. In a plant-sandy soil system, depletion of P in resin-P and NaOH-Pi fractions was attributed to plant uptake rather than conversion into less available P forms (e.g. from NaOH-Pi to H2SO4-P). High-ash biochars with high P concentrations could be potential slow-release P sources with high-agronomic values. To determine appropriate agronomically effective rates of application and avoid the risk of eutrophication associated with biochar application, it is recommended to determine available P using 2% formic acid extraction in biochars, so that dose, frequency and timing of application are correctly established. All the information obtained in this thesis will support the future use of the biochar technology to recycle nutrients and stabilise carbon from agricultural and municipal organic wastes of good quality.Item Stability of biochar and its influence on the dynamics of soil properties : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Soil Science, Institute of Natural Resources, College of Sciences, Massey University, Palmerston North, New Zealand(Massey University, 2012) Herath, Herath Mudiyanselage Saman KumaraThe overall objective of this PhD was to investigate the stability of specific biochars – produced from corn stover (Zea mays L.) at 350 °C (CS-350) and 550 °C (CS-550) – and their roles on the dynamics of native organic matter (NOM) and physical properties of a Typic Fragiaqualf (Tokomaru soil; TK soil) and a Typic Hapludand (Egmont soil; EG soil). Except for the controls, all other treatments received a 7.18 t C ha–1 application, either as fresh corn stover or as biochar. After 295 d, bulk density, saturated hydraulic conductivity (Ks), volumetric moisture content (θV), aggregate stability and soil water repellency were measured. At that sampling time, two undisturbed subsamples from each pot were taken: (i) in one subsample, lucerne (Medicago sativa L.) was seeded; (ii) in the other, the incubation was continued without plants. All pots were additionally incubated for 215 d. During the 510 d incubation, the CO2-C efflux rate was determined for the selected 82 d, and samples for 19 d out of these 82 d were analysed for δ13CO2. Soil samples at T0, T295 and T510 (with and without plants) were physically fractionated into coarse and fine free particulate organic matter (fPOM), silt+clay, and heavy fraction (HF), and analysed for δ13C and total OC. Dichromate oxidation and acid hydrolysis were also conducted for the bulk soil and physical fractions. Biochar application significantly increased (P<0.05) the aggregate stability of both soils (the effect of CS-550 biochar being more prominent in the TK soil than that in the EG soil, and the reverse pattern being observed for the CS-350 biochar), and the volumetric moisture content (θV). The latter effect was generally more evident in the TK soil than that in the EG soil, at both T0 and T295. Biochar addition significantly (P<0.05) increased the macroporosity in the TK soil and also the mesoporosity in the EG soil. Biochar also significantly increased (P<0.05) Ks of the TK soil but not that of the EG soil. However, biochar was not found to increase water repellency of these soils. Overall, the results suggest that these biochars may facilitate drainage in the poorly drained TK soil and potentially reduce N 2O emissions. Total accumulated CO2-C evolved from the corn stover treatment was significantly higher (P<0.05) than that from rest of the treatments. No significant differences (P<0.05) were observed in the rate of CO2-C evolution between the controls and biochar treatments. In both soils, fresh corn stover had a net positive priming effect on the NOM decomposition, while biochar had a net negative priming effect in the TK soil, but no effect in the EG soil. When a C balance was made considering the C lost during pyrolysis, the combination of CS-350 biochar and EG soil provided the greatest C saving of all treatments. When the different priming effects on NOM were also considered, differences among the two soils were balanced. The longer half-life (494 y) corresponded to the CS-550 biochar in the TK soil, while the half-lives of the other biochar-soil combinations were <200 y. It was estimated that 55 – 70 % of amended biochar-C would remain in soil after 100 y. After 295 d, >78 % of biochar-C recovered in the TK soil and >64 % of biochar C in the EG soil ended in the coarse fPOM, >13 % (TK) and >21 % (EG) in the fine fPOM fraction, and the rest in the silt+clay fraction. The same pattern was observed after 510 d, both with and without plants. Most of the biochar particles thus concentrated into the “unprotected pool”. The use of dichromate oxidation to distinguish the recalcitrant fraction of C in the “unprotected pool” is suggested. Finally, the presence of both biochar and plants induced an additional accumulation of total organic carbon (OC) in the TK-350 and EG-550 soils (P<0.05), compared with the treatments with plants but no biochar. The use of biochars in these OC-rich soils was proven to be adequate to promote C sequestration, especially when compared to the direct application of the fresh feedstock. This enhanced C sequestration is suggested to occur through (i) the addition of a stable C source (e.g., condensed aromatic C in biochar), (ii) the protection of NOM (especially in the TK soil), and (iii) the interaction of biochar with new OC inputs to soil (e.g., root exudates). The results from this study also indicated that long-term incubations in the absence of a continuous fresh input of plant material may create artefacts such as reduced aggregate protection and an apparent loss of aggregate protected OC. Future research should be directed to investigate (i) the influence of these physicochemical changes on microbial activity, population and diversity; and (ii) the evolution of these interactions under field conditions.