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    Redox-induced phosphorus release from critical source areas following rainfall events in New Zealand
    (Elsevier Ltd, United Kingdom, 2025-02) Palihakkara J; Burkitt L; Jeyakumar P; Attanayake CP
    Critical source areas (CSAs) can act as a source of phosphorus (P) during intermittent rainfall events and contribute to dissolved P loss via runoff. Dissolved forms of P are readily accessible for plant and algal uptake; hence it is a concern in terms of the eutrophication of freshwater bodies. The potential of CSAs to release dissolved P to surface runoff upon intermittent short-term submergence caused by different rainfall events has not been studied at a field-scale in New Zealand previously. A field study was conducted to investigate the potential of two different pastoral soil CSAs (Recent and Pallic soil) to release soil P over five rainfall events during winter and to explore the mechanisms of P release in these soils. Ten sampling stations were installed within each CSA in an area of 6 × 2 m2. Each sampling station had two porewater samplers installed at two depths (2 and 10 cm) below the soil surface. Two platinum half-cell electrodes were installed at the same two depths. Porewater and floodwater samples were collected following five rainfall events. Redox potentials were measured in-situ. Dissolved reactive phosphorus (DRP), pH, dissolved organic carbon, cations, anions, and alkalinity of the water samples were measured. Soil chemical P fractions were assessed at the beginning, middle and end of the experiment. Thermodynamic modelling was used to infer dissolution and formation of P and P-associated minerals. The average porewater DRP at the two depths during the rainfall events of the Recent and Pallic soils were 0.32-1.3 mg L-1 and 0.26-2.31 mg L-1, respectively. The average floodwater DRP concentrations of the Recent and Pallic soils were 35 and 43-fold higher than the target DRP concentration (0.01 mg L-1) for the Manawatū River. The study highlights the substantial risk of P loss from CSAs to surface water, driven primarily by the reductive dissolution of Fe and Mn oxy(hydr)oxides. The findings underscore the importance of targeted management strategies to mitigate dissolved P runoff, particularly in high-risk CSAs frequent submerged during rainfall events. This study developed an effective method for monitoring soil porewater P and redox conditions, offering valuable insights and practical tools for resource managers seeking to reduce P contamination.
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    Requirement of digestible calcium at different dietary concentrations of digestible phosphorus for broiler chickens 3. Broiler finishers (d 25 to 35 post-hatch)
    (y Elsevier Inc (USA), on behalf of Poultry Science Association Inc, 2023-04) David LS; Abdollahi MR; Bedford MR; Ravindran V
    An experiment was conducted to determine the digestible calcium (Ca) and digestible phosphorous (P) requirements of 25 to 35-day-old broiler chickens. Fifteen corn-soybean meal-based diets containing 2.0, 2.5, 3.0, 3.5, and 4.0 g/kg standardized ileal digestible (SID) Ca and 2.5, 3.5, and 4.5 g/kg SID P were fed to broilers from d 25 to 35 post-hatch. Each experimental diet was randomly allocated to 6 replicate cages (8 birds per cage). Body weight and feed intake were recorded, and the feed conversion ratio was calculated. On d 35, birds were euthanized to collect the ileal digesta, tibia, and carcass for the determination of ileal Ca, and P digestibility, concentrations of ash, Ca, and P in tibia and the retention of Ca and P in the carcass. Titanium dioxide (5.0 g/kg) was included in all diets as an indigestible indicator for the ileal digestibility measurement. Feed intake and total excreta output were measured during the last 4 d of the experimental period for the measurement of apparent total tract retention of Ca and P. Fixed effects of the experiment were dietary concentrations of SID Ca and SID P and their interaction. If the interaction or main effects were significant (P < 0.05), the parameter estimates for second-order response surface model (RSM) were determined using General Linear Model procedure of SAS. The maximum response was not predicted for most of the parameters (including growth performance and tibia) as the Ca effect was linear which indicated that the highest level of Ca employed in the study may have not been high enough. The requirement of dietary SID Ca for maximization of these parameters, therefore, depends on the dietary SID P concentration when the dietary SID Ca is within 2.0 to 4.0 g/kg. However, based on the factorial analysis, the highest weight gain was observed at 3.5 g/kg SID P and 3.5 g/kg SID Ca concentrations. Tibia ash was higher in birds fed 4.5 g/kg SID P and was unaffected by dietary SID Ca concentrations. However, based on overall findings, a combination of 3.5 g/kg SID P and 3.0-3.5 g/kg SID Ca may be recommended for the optimum tibia ash. The recommended SID Ca requirements (at 3.5 g/kg SID P) for weight gain (3.5 g/kg or 6.4 g/kg total Ca) and tibia ash (3.0-3.5 g/kg or 5.5-6.4 g/kg total Ca) are lower than the current Ca recommendations (7.8 g/kg total Ca equivalent to 4.25 g/kg SID Ca; Ross, 2019) for broiler finishers, suggesting possible excess of Ca in diets formulated based on the current recommendation.
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    Enhanced biological N2 fixation and yield of faba bean (Vicia faba L.) in an acid soil following biochar addition: dissection of causal mechanisms
    (Springer Nature, 2015-10) Van Zwieten L; Rose T; Herridge D; Kimber S; Rust J; Cowie A; Morris S; Lehman J
    Background and aims: Acid soils constrain legume growth and biochars have been shown to address these constraints and enhance biological N2 fixation in glasshouse studies. A dissection of causal mechanisms from multiple crop field studies is lacking. Methods: In a sub-tropical field study, faba bean (Vicia faba L.) was cultivated in rotation with corn (Zea mays) following amendment of two contrasting biochars, compost and lime in a rhodic ferralsol. Key soil parameters and plant nutrient uptake were investigated alongside stable 15 N isotope methodologies to elucidate the causal mechanisms for enhanced biological N2 fixation and crop productivity. Results: Biological N2 fixation was associated with plant Mo uptake, which was driven by reductions in soil acidity following lime and papermill (PM) biochar amendment. In contrast, crop yield was associated with plant P and B uptake, and amelioration of soil pH constraints. These were most effectively ameliorated by PM biochar as it addressed both pH constraints and low soil nutrient status. Conclusions: While liming resulted in the highest biological N2 fixation, biochars provided greater benefits to faba bean yield by addressing P nutrition and ameliorating Al toxicity.
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    Requirement of digestible calcium at different dietary concentrations of digestible phosphorus for broiler chickens. 2. Broiler growers (d 11 to 24 post-hatch)
    (Elsevier Inc. on behalf of Poultry Science Association Inc., 2022-11) David LS; Abdollahi MR; Bedford MR; Ravindran V
    An experiment was conducted to determine the digestible calcium (Ca) and digestible phosphorous (P) requirements of 11 to 24 d old broiler chickens. Eighteen corn-soybean meal-based diets containing 1.80, 2.35, 2.90, 3.45, 4.00, and 4.55 g/kg standardized ileal digestible (SID) Ca and 3.5, 4.5, and 5.5 g/kg SID P were fed to broilers from d 11 to 24. Each experimental diet was randomly allocated to six replicate cages (8 birds per cage). Body weight and feed amount were recorded at the start and end of the experiment and the feed conversion ratio was calculated. On d 24, birds were euthanized to collect ileal digesta, tibia, and carcass for the determination of digestible Ca and P, the concentration of ash, Ca and P in tibia and the retention of Ca and P in the carcass, respectively. Titanium dioxide (5 g/kg) was included in all diets as an indigestible indicator for apparent ileal digestibility measurement. Total excreta output was measured during the last 4 d of the experimental period for the measurement of apparent total tract retention of Ca and P. Fixed effects of the experiment were dietary concentrations of SID Ca and SID P and their interaction. If the interaction or main effect was significant (P < 0.05), the parameter estimate for second-order response surface model was determined using General Linear Model procedure of SAS. The weight gain of broiler growers was optimized at the SID P concentration of 3.5 g/kg and SID Ca concentrations between 2.35 and 4.00 g/kg. At 3.5 g/kg SID P concentration, the required SID Ca for maximum weight gain was determined to be 3.05 g/kg, which corresponded to SID Ca to SID P ratios of 0.87. The concentration of SID Ca that maximized tibia ash at 3.5 g/kg SID P was 3.69 g/kg, which corresponded to SID Ca to SID P ratio of 1.05. Maximizing bone ash requires more Ca than maximizing weight gain. Carcass Ca and P retention were reflective of total tract Ca and P retention values. The estimated SID Ca requirements (at 3.5 g/kg SID P) for both maximized weight gain (3.05 g/kg or 6.11 g/kg total Ca) and bone ash (3.69 g/kg or 7.28 g/kg total Ca) are lower than the current Ca recommendation (8.70 g/kg total Ca equivalent to 4.03 g/kg SID Ca; Ross, 2019) for broiler growers, indicating possible oversupply of Ca in diets formulated based on the current recommendation.
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    Nutrient criteria to achieve New Zealand's riverine macroinvertebrate targets
    (PeerJ, Inc, 2021) Canning AD; Joy MK; Death RG; Brauns M
    Waterways worldwide are experiencing nutrient enrichment from population growth and intensive agriculture, and New Zealand is part of this global trend. Increasing fertilizer in New Zealand and intensive agriculture have driven substantial water quality declines over recent decades. A recent national directive has set environmental managers a range of riverine ecological targets, including three macroinvertebrate indicators, and requires nutrient criteria be set to support their achievement. To support these national aspirations, we use the minimization-of-mismatch analysis to derive potential nutrient criteria. Given that nutrient and macroinvertebrate monitoring often does not occur at the same sites, we compared nutrient criteria derived at sites where macroinvertebrates and nutrients are monitored concurrently with nutrient criteria derived at all macroinvertebrate monitoring sites and using modelled nutrients. To support all three macroinvertebrate targets, we suggest that suitable nutrient criteria would set median dissolved inorganic nitrogen concentrations at ~0.6 mg/L and median dissolved reactive phosphorus concentrations at ~0.02 mg/L. We recognize that deriving site-specific nutrient criteria requires the balancing of multiple values and consideration of multiple targets, and anticipate that criteria derived here will help and support these environmental goals.
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    Effects of a novel consensus bacterial 6-phytase variant on the apparent ileal digestibility of amino acids, total tract phosphorus retention, and tibia ash in young broilers
    (Oxford University Press, 2022-02-01) Dersjant-Li Y; Abdollahi MR; Bello A; Waller K; Marchal L; Ravindran V
    The effect of a novel consensus bacterial 6-phytase variant (PhyG) on apparent ileal digestibility (AID) of amino acids (AA) and phosphorus (P) utilization in young broilers when added to diets with high phytate-P (PP) content without added inorganic phosphate (Pi) and deficient in digestible (dig) AA and metabolizable energy (ME) was investigated. A total of 256 Ross 308 male broilers were assigned to 4 treatments (8 birds/cage, 8 cages/treatment) in a completely randomized design. Treatments comprised a positive control (PC, 2,975 kcal/kg ME, 3.7 g/kg dig P, 2.83 g/kg PP, 8.4 g/kg Ca, 10.6 g/kg dig lysine), a negative control (NC) without added Pi (ME −68 kcal/kg, crude protein −10 g/kg, dig AA −0.1 to −0.4 g/kg, Ca −2.0 g/kg, dig P −2.2 g/kg, Na −0.4 g/kg vs. PC), and NC plus 500 or 1,000 FTU/kg of PhyG. Test diets were corn/soy/rapeseed-meal/rice-bran-based and fed from 5 to 15 d of age. Ileal digesta and tibias were collected on day 15. Excreta was collected during days 12 to 15 to determine P retention. The NC (vs. PC) reduced (P < 0.05) P retention (−10.4% units), tibia ash (−14.3% units), weight gain (−109 g), feed intake (−82 g) and increased FCR (from 1.199 to 1.504), confirming that the NC was extremely deficient in nutrients and energy. Phytase addition to the NC linearly (P < 0.001) improved performance, but did not fully recover it to the level of the PC due to the severe nutrients/energy reduction in NC. Phytase linearly increased P retention (P < 0.001), tibia ash (P < 0.001), AID of dry matter (P < 0.05), nitrogen (P < 0.01), gross energy (P < 0.05), and all 17 individual AA (P < 0.01). At 1,000 FTU/kg, phytase increased (P < 0.05) P retention vs. PC and NC (+14.5 and +24.9% units, respectively) and increased tibia ash vs. NC (+13.8% units), equivalent to PC. The NC decreased AID of Cys, Gly, Thr, and Met vs. PC (P < 0.05). At 1,000 FTU/kg, phytase increased AID of all 17 AA vs. NC (P < 0.01), equivalent to PC. At 1,000 FTU/kg, AID AA responses (above NC) ranged from +4.5% (Met) to +15.0% (Cys), being maximal for essential Thr (+10.4%) and Val (+8.2%) and non-essential Cys (+15.0%) and Gly (+10.4%). The results highlight the efficacy of PhyG at a dose level of 500 to 1,000 FTU/kg in young broilers for improving the ileal digestibility of nitrogen, AA, and energy alongside P retention and tibia ash. The performance data emphasize the need to consider digestible nutrient intake as a response variable in exogenous enzyme studies.
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    Environmental influences on polyphosphate accumulation in microalgae : an investigation into species differences and transcriptional responses : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering at Massey University, Manawatū, New Zealand
    (Massey University, 2022) Cliff, Alexander
    Many species of microalgae can store phosphorus (P) as polyphosphate (polyP) granules during the process of ‘luxury uptake’, a term describing intracellular P accumulation above levels required for normal metabolism (0.2 – 1% P by dry weight). Environmental conditions can influence P luxury uptake but it is not known whether the effects of environmental conditions on luxury P uptake are the same for all microalgae or whether all microalgae can in fact store P as polyP. The broad aim of the work described in this thesis was to extend the current knowledge of polyphosphate (polyP) synthesis in microalgae, enabling improved exploitation of their ability to sequester P from water sources and enhance recovery of a vital nutrient. Specifically, the mechanisms by which environmental conditions influence luxury uptake and potential species differences need to be studied to better understand observations at the population level and make informed decisions in the design of treatment processes. The experimental work was therefore divided into two main objectives: Objective 1 sought to determine whether there were in fact differences in luxury uptake ‘abilities’ between species. In Chapter 3, this is explored through the use of genetic database searches, biochemical assays, and protein modelling. Objective 2 examined the effects of environmental factors known to influence luxury uptake. In Chapter 4, the responses of the microalgae Chlamydomonas reinhardtii and Chlorella vulgaris to P repletion were studied in a range of conditions to identify similarities and differences in environmental influences. Chapter 5 sought to determine whether the observed differences could be due to responses at the genetic level, by comparing the gene expression levels of P-related genes in C. reinhardtii under selected sets of conditions from the previous chapter. An additional experiment was conducted, to examine gene expression without inducing ‘noise’ through changes in growth conditions, and this is discussed in Chapter 6. Using protein sequence homology searches, phylogenetic tree generation, protein structure modelling, and biochemical assays (using the chlorophytes C. reinhardtii, C. vulgaris, Desmodesmus cf. armatus, Gonium pectorale, Pediastrum boryanum, and the cyanobacterium Microcystis aeruginosa), it was shown that the ability to store P as polyP is common among microalgae, as implied by the broad conservation of the polyP polymerase VTC4, but luxury uptake abilities vary between species. All six tested microalgae responded to P addition following a period of P depletion by accumulating P as granular polyP. Under the conditions tested, the total P assimilated over 24 hours was similar for five of the microalgae tested (2.6 – 3.6% P by dry weight) but C. vulgaris assimilated considerably less P (~1.2% P) than the others. The effects of environmental conditions on P uptake and polyP accumulation were assessed by triggering luxury uptake in C. vulgaris and C. reinhardtii in different conditions of light supply, temperature, and pH, with different P repletion doses following different P depletion times. P uptake and polyP accumulation were influenced by light supply, P depletion time, and P repletion dose in both microalgae but P dose had the strongest influence in C. reinhardtii versus light supply in C. vulgaris. PolyP was still accumulated by these two species in conditions suppressing growth and severely repressing metabolism (10 °C and darkness), evidencing that P uptake and polyP synthesis do not require light energy. The model alga C. reinhardtii was then used to evaluate, for the first time, whether the differences in P uptake and polyP accumulation observed with respect to differences in environmental conditions were associated with differences in gene expression. Although the genes assessed were downregulated (relative to controls) 24 hours after P repletion, as expected, in all experimental conditions, changing conditions at the start of the experiment also caused changes in gene expression in controls, making it hard to distinguish responses to P repletion from ‘global’ responses to changing conditions. Another experiment was therefore performed where temperature and light intensity were maintained constant before and after P repletion. The results confirmed that increased P repletion dose and P depletion time were associated with increased P uptake and polyP accumulation over 24 hours. The results evidenced the expected downregulation of PSR1, VTC4, VTCX, and PTB5 after 1 hour of P repletion, but this response was much more salient after 7 days of P depletion (compared to 3 days). Changes in gene expression were also associated with P repletion dose, but only after 7 days of P depletion. This showed that the response to P repletion is stronger after a longer P depletion time but the observed expression changes did not support the hypothesis that these changes were the reason for the higher observed P uptake and polyP accumulation. For the first time, it has been systematically shown that the ability to accumulate P as polyP is widespread among microalgae but that the kinetics of P accumulation vary between species and this species-dependence is influenced by environmental factors. These factors engender differences at the level of gene expression, involving both components of the VTC complex and phosphate transporters. However, the differences in P uptake and polyP accumulation may be better understood by investigating the structural differences and changes in activity of relevant proteins.
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    Factors affecting phosphate concentrations in surface and subsurface runoff from steep East Coast hill country : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Applied Science, Department of Soil Science, Massey University
    (Massey University, 1998) Blennerhassett, Jamie D
    Eutrophication is a problem receiving much attention within New Zealand and throughout the rest of the world. Problems associated with eutrophication cause major financial, aesthetic and recreational costs to not only commercial and recreational water users but to society in general. The major nutrient of concern in relation to eutrophication is phosphorus (P) as it is often considered to be the limiting factor. The two major areas from which P enters waterways are point sources and non-point sources. Point sources are relatively easy to identify and quantify. Non-point sources however, are less easy to quantify due to the size of areas from which P is sourced and the number of varying factors which can affect the amount of P which is lost to water-ways. This study investigated P concentrations in surface runoff and subsurface flow from steep east coast hill country. Factors studied included aspect, soil P status, season and fertiliser addition. The study was carried out on grazed pasture farmlets, in which there were 'High P' and 'Low P' fertiliser regimes. Each regime had north and south facing aspects. Four sites were used in the study. High P North (HPN), High P South (HPS), Low P North (LPN) and Low P South (LPS). Simulated rainfall was applied to the sites and surface runoff samples were collected and analysed for dissolved reactive phosphate concentration (DRP). Superphosphate fertiliser was then applied at 20 kg P ha-1 to each site and the runoff procedure was repeated 7 weeks and 14 weeks the lower P soil test values on the south-facing slopes. A water extractable P test provided a better correlation with runoff DRP concentrations for individual runoff events than the Olsen P test. Both tests however, provided poor correlations when all of the Runs were combined. This was due largely to the large increase in DRP concentrations in surface runoff in Run 3 with no corresponding increase in soil tests. There was no apparent relationship between fertiliser regime i.e. soil P status, and the concentration of DRP in subsurface runoff. In Run 3 however, there was a marked increase in subsurface DRP concentration for both sites which was consistent with the surface runoff results and supported the theory of soil moisture playing a major role in determining the DRP concentration in water. The study suggests that the greatest risk of P loss from soil to surface waters will be from northerly aspects with high fertiliser histories during the summer months when soil moisture levels are low.
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    Characterisation of nutrition responses in three genotypes of white clover (Trifolium repens L.) selected for tolerance to low phosphorus : a thesis presentation in partial fulfilment of the requirements for the degree of Master of Science in Plant Molecular Biology at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Smith, Diantha
    This study focused on the differences in root system architecture (RSA) of three white clover (Trifolium repens L.) genotypes, designated 43-7, 45-14 and 47-9 that were isolated from breeding lines selected to tolerate low phosphorus (P). In this study, genetically identical white clover stolons were cut from stock plants at the fourth node, and primary roots emerged (post excision) from either of the two primordia at nodes three or four. The main objective was to establish if differences in RSA were observed in response to a limited P-supply (10 μM KH2PO4) compared with a sufficient P-supply (1 mM KH2PO4). Each of the cut stolons had a dominant primary root that was nominated to be used for the analysis of root growth in terms of elongation and lateral root emergence. The analysis was standardised by designating the branching zone as the region of the primary root that contained visible lateral roots. The remaining region was designated the elongation zone, and did not contain visible lateral roots. In P-sufficient media, the branching zone was approximately 50% of the primary root length by 15 days post excision and approximately 80% by 25 days in the three genotypes. After 30 days post excision, the branching zone was maintained between 85% and 90% of the primary root length. The response to low P was measured after the emergence of visible lateral roots in experiment I and prior to the emergence of visible lateral roots in experiment II. A third treatment group with a reduced sulfur supply (in experiment II) tested the specificity of the P-stress response. In summary, the morphological responses to P-stress were characteristic for each genotype; the changes to the primary and/or lateral roots occurred within seven days from the reduction in P-supply; and the timing of the reduction in P-supply influenced the degree of the response that was observed with respect to the branching zone. The responses to P-stress included a stimulation of the primary and lateral roots in 47-9 with a reduced root biomass under S-stress; a decrease in the number of visible lateral roots in 45-14; and the decreased elongation of lateral roots in 43-7, which reduced the initiation of tertiary roots. The branching zone decreased in 45-14 only when the P-supply was changed after lateral root emergence. In contrast, the branching zone increased in 47-9 only when the P-supply was changed before lateral root emergence. The results suggest that the P-stress response in the roots is specific and utilisation of P and S may differ in the three genotypes.
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    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, Tao
    Biochar 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.