Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. 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 Tao Wang 2013 I ABSTRACT 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 II 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 III 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 IV 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. V ACKNOWLEDGEMENTS First of all, I would like to express my deepest gratitude to my supervisors A/Prof Dr Marta Camps-Arbestain and Prof Dr Mike Hedley for their continuous support and great guidance during my PhD study. They provided a very enjoyable and relaxed atmosphere for me to study and work in. They are always ready to share their great enthusiasm for research, immense knowledge in soil science and fabulous experience in writing. I gratefully acknowledge Massey University for providing me a fellowship and the Ministry for Primary Industries (former the Ministry of Agriculture and Forestry) New Zealand for funding the research. My sincere appreciation is extended to Drs Peter Bishop and Roberto Calvelo- Pereira for their kind help, stimulating discussions and invaluable suggestions to my study. Staffs of the Soils Lab ? Ms Glenys Wallace, Dr James Hanly, Mr Bob Toes, Mr Mike Bretherton, Mr Ian Furkert, Mr Lance Currie, and Mr Ross Wallace are acknowledged for their technical supports. Thanks also goes to Ms Denise Stewart, Ms Liza Haarhoff and Ms Sandra Dunkinson for their kind help with all sorts of paperwork; A/Professor Bob Stewart, Prof. Felipe Mac?as (Universidad de Santiago de Compostela, Spain) and Dr Jason Hindmarsh (IFNHH, Massey) for their assistance with XRD, FTIR and NMR analyses respectively; and whomever help me during my study and stay in New Zealand. A special thanks goes to all my friends back in China and here in New Zealand: Congying Wang, Guifen Yu, Fenxia Yao, Yuechun Zeng, Guangbin Zhang, Tianran Sun, Qinhua Shen, Yuancheng Wang, Tomoko Maruyama, Linda Moore, Sam Dermody, Ainsley Dermody, Saman Herath, Indika Herath, Pullanagari Reddy, Erwin VI Wisnubroto, Alnul, Richard Self, Riaz, Sadaf, Neha and Sole etc. (listed in no particular order) for sharing happiness and making my life overseas extremely enjoyable. I would also like to extend my sincere appreciation to the reviewers of my thesis: Prof Tim Clough (Lincoln University, New Zealand), Prof Josep M. Alcaniz (Universitat Aut?noma de Barcelona, Spain) and Dr Bambang Kusumo (Massey University and University of Mataram, Indonesia) for their time reading the thesis and invaluable suggestions for improving it. Lastly, but most importantly, I would like to express my heartfelt thanks to my family (parents, brother, sister, grandparents, aunts and uncles) for being a constant source of love, concern, support and strength all these years. VII TABLE OF CONTENTS ABSTRACT ..................................................................................................................... I ACKNOWLEDGEMENTS ........................................................................................... V TABLE OF CONTENTS ............................................................................................ VII LIST OF TABLES ........................................................................................................ XI LIST OF FIGURES ..................................................................................................... XII ACRONYMS ................................................................................................................ XV CHAPTER 1. GENERAL INTRODUCTION ................................................................. 1 1.1 General background ................................................................................................ 2 1.2 Research objectives ................................................................................................ 5 1.3 Thesis outline .......................................................................................................... 6 References .................................................................................................................... 7 CHAPTER 2. LITERATURE REVIEW ........................................................................ 13 2.1 Organic wastes ...................................................................................................... 14 2.1.1 Organic wastes and their treatment .............................................................. 14 2.1.2 Greenhouse gas (GHG) emissions from organic waste streams ................... 17 2.2 Pyrolysis of organic waste to biochars ................................................................. 21 2.2.1 A sustainable biochar concept ....................................................................... 22 2.2.2 Indices for stability of C in biochar ............................................................... 24 2.3 Nutrients in biochars and their bioavailability ..................................................... 26 2.3.1 Influencing factors of nutrient properties of biochar .................................... 27 2.3.2 Nitrogen ......................................................................................................... 27 2.3.3 Phosphorus .................................................................................................... 29 2.3.4 Methodologies used for characterisation of available N and P in biochars . 30 2.3.5 Other nutrient elements ................................................................................. 31 2.4 Pollutants in biochars and their bioavailability .................................................... 32 2.5 Current research demand for the characterisation of biochars produced from organic waste streams in New Zealand ...................................................................... 35 References .................................................................................................................. 36 CHAPTER 3. PREDICTING C AROMATICITY OF BIOCHARS BASED ON THEIR ELEMENTAL COMPOSITION .................................................................................... 43 Abstract ....................................................................................................................... 44 Keywords .................................................................................................................... 44 3.1 Introduction .......................................................................................................... 45 3.2 Materials and methods .......................................................................................... 46 3.2.1 Biochar preparation and characterisation .................................................... 46 3.2.2 Data collection and modelling ...................................................................... 48 3.3 Results and discussion .......................................................................................... 52 3.3.1 General description of biochars .................................................................... 52 3.3.2 Calibration of the models .............................................................................. 55 3.3.3 Comparison and validation of models ........................................................... 58 3.3.4 Notes for future users of Models 1 and 2 and suggestions to future research ................................................................................................................................ 59 3.4 Conclusion ............................................................................................................ 60 Acknowledgements .................................................................................................... 61 References .................................................................................................................. 61 CHAPTER 4. DETERMINATION OF CARBONATE-C IN BIOCHARS .................. 65 Abstract ....................................................................................................................... 66 Keywords .................................................................................................................... 66 VIII 4.1 Introduction .......................................................................................................... 67 4.2 Materials and methods .......................................................................................... 69 4.2.1 Biochars ......................................................................................................... 69 4.2.2 Determination of carbonate-C via a coulometric titration ........................... 69 4.2.3 Thermogravimetric and derivative thermogravimetric (TG/DTG) analysis . 70 4.2.4 Carbonate-C removal with acid fumigation .................................................. 71 4.2.5 A bubble test for the selection of carbonate-rich biochars ........................... 71 4.2.6 Data analysis ................................................................................................. 72 4.3 Results and discussion .......................................................................................... 73 4.3.1 Selected properties of biochars ..................................................................... 73 4.3.2 Comparison of methods to determine carbonate-C in biochars ................... 74 4.3.3 Simple tests for screening samples for accurate carbonate-C analysis ........ 80 4.4 Conclusion ............................................................................................................ 83 Acknowledgements .................................................................................................... 84 References .................................................................................................................. 84 CHAPTER 5. CHEMICAL AND BIOASSAY CHARACTERISATION OF NITROGEN AVAILABILITY IN BIOCHARS PRODUCED FROM DAIRY MANURE AND BIOSOLIDS ....................................................................................... 87 Abstract ....................................................................................................................... 88 Keywords .................................................................................................................... 89 5.1 Introduction .......................................................................................................... 89 5.2 Material and methods ........................................................................................... 91 5.2.1 Feedstock and biochar preparation .............................................................. 91 5.2.2 Acid hydrolysis and N determination ............................................................ 92 5.2.3 Thermogravimetric and derivative thermogravimetric (TG/DTG) analysis . 93 5.2.4 Chemical oxidation ........................................................................................ 94 5.2.5 Incubation study for C and N turnover .......................................................... 94 5.2.6 Data analysis ................................................................................................. 96 5.3 Results .................................................................................................................. 97 5.3.1 Biochar characterisation ............................................................................... 97 5.3.2 N forms in biochar solubilised by acid hydrolysis ........................................ 97 5.3.3 DTG curve ................................................................................................... 102 5.3.4 Chemical oxidation by K2Cr2O7 acid solution ............................................ 102 5.3.5 C and N turnover in feedstock and biochar ................................................. 106 5.4 Discussion ........................................................................................................... 107 5.4.1 C and N change during pyrolysis, acid hydrolysis and chemical oxidation 107 5.4.2 C turnover .................................................................................................... 111 5.4.3 N lability in biochar ..................................................................................... 113 5.5 Conclusion .......................................................................................................... 116 Acknowledgements .................................................................................................. 117 References ................................................................................................................ 117 CHAPTER 6. PREDICTING PHOSPHORUS BIOAVAILABILITY FROM HIGH- ASH BIOCHARS ......................................................................................................... 123 Abstract ..................................................................................................................... 124 Keywords .................................................................................................................. 124 6.1 Introduction ........................................................................................................ 125 6.2 Materials and methods ........................................................................................ 127 6.2.1 Feedstocks and biochar preparation ........................................................... 127 6.2.2 Biochar characterisation ............................................................................. 128 6.2.3 Phosphorus extraction and analysis ............................................................ 129 IX 6.2.4 Metal analysis and X-ray diffraction (XRD) analysis ................................. 130 6.2.5 Bioassay test ................................................................................................ 130 6.2.6 Model and data analysis .............................................................................. 132 6.3 Results ................................................................................................................ 133 6.3.1 Biochar characterisation ............................................................................. 133 6.3.2 Phosphorus and cation extractability in feedstocks and biochars .............. 134 6.3.3 Ryegrass yield and P uptake ........................................................................ 141 6.4 Discussion ........................................................................................................... 144 6.5 Conclusion .......................................................................................................... 148 Acknowledgements .................................................................................................. 149 References ................................................................................................................ 149 CHAPTER 7. THE FATE OF PHOSPHORUS OF ASH-RICH BIOCHARS IN A SOIL-PLANT SYSTEM .............................................................................................. 153 Abstract ..................................................................................................................... 154 Keywords .................................................................................................................. 154 7.1 Introduction ........................................................................................................ 155 7.2 Materials and methods ........................................................................................ 157 7.2.1 Feedstocks and biochar preparation and characterisation ........................ 157 7.2.2 Greenhouse experiment ............................................................................... 157 7.2.3 Olsen and acid ammonium oxalate extraction ............................................ 159 7.2.4 Soil P fractionation ...................................................................................... 159 7.2.5 Release of P via successive resin extractions .............................................. 160 7.2.6 Data analysis ............................................................................................... 160 7.3 Results ................................................................................................................ 161 7.3.1 Biochar characterisation and soil available P test ..................................... 161 7.3.2 Plant yields and P uptake ............................................................................ 162 7.3.3 P fractionation ............................................................................................. 167 7.3.4 P release kinetics via successive resin extractions ...................................... 167 7.4 Discussion ........................................................................................................... 170 7.4.1 Soil P tests for soils amended with biochars ............................................... 170 7.4.2 P forms and availability .............................................................................. 171 7.4.3 Transformation of P forms .......................................................................... 173 7.5 Conclusion .......................................................................................................... 176 Acknowledgements .................................................................................................. 177 References ................................................................................................................ 177 CHAPTER 8. OVERALL SUMMARY AND RECOMMENDATIONS FOR FUTURE RESEARCH ................................................................................................................. 181 8.1 Overall summary ................................................................................................ 182 8.1.1 Carbon in biochars ...................................................................................... 182 8.1.2 Availability of N in biochars ........................................................................ 184 8.1.3 Availability of P in biochars ........................................................................ 185 8.1.4 Highlights of this thesis ............................................................................... 187 8.2 Recommendations for future research ................................................................ 188 References ................................................................................................................ 190 APPENDIX .................................................................................................................. 191 Appendix I. Supporting information for Chapter 3 (S3) ............................................ A1 Materials and methods ........................................................................................... A1 References ............................................................................................................... A6 Appendix II. Supporting information for Chapter 4 (S4) ........................................... A8 References ............................................................................................................. A12 X Appendix III. Supporting information for Chapter 5 (S5)........................................ A13 Modelling ammonia volatilization from the biochar-sand mixtures in a sealed jar .............................................................................................................................. A15 References ............................................................................................................. A16 Appendix IV. Supporting information for Chapter 7 (S7) ....................................... A17 XI LIST OF TABLES Table 2-1. Nitrogen release during pyrolysis by model compounds and biomass. Source: Becidan et al (2007) ................................................................................................... 28 Table 3-1. Elemental composition (dry-ash free basis, daf) and predicted aromaticity (fa- pre) of biochars treated and untreated (original) with 10% HF solution. fa-exp is the measured fa by DP/NMR techniques. Data were presented as mean?standard deviation (n=2). 100% of aromaticity was set as 1 fa-unit. RMSE was calculated after excluding BSe-250 and MAe-250. M denotes model and n/a not applicable. .......... 49 Table 4-1. Selected properties of biochars used in this study ........................................ 76 Table 4-2. Carbonate-C determined by different methods ............................................. 77 Table 4-3. Correlation matrix of carbonate-C in biochars determined by various methods. ..................................................................................................................... 78 Table 5-1. Selected properties of biochar samples ...................................................... 100 Table 5-2. C, N and organic N forms in whole samples of feedstock (F) and biochar (pyrolysed at different temperatures) and in fractions produced from 6 M HCl hydrolysis (n.d., not detected), ?standard deviation (n=3). ..................................... 101 Table 5-3. TG analysis of biochars and their non-hydrolysable residues .................... 104 Table 5-4. Changes in C and N in biochars after K2Cr2O7 oxidation ........................... 105 Table 5-5. Estimation of C turnover dynamics of the decomposable fraction of C in biochars (the recalcitrant fraction is thus not included) fitted to a two-component decay model. ............................................................................................................ 107 Table 6-1. Selected properties of Waitarere sandy soil ................................................ 136 Table 6-2. Selected properties of biochars used in this study ...................................... 136 Table 6-3. Phosphorus extractability of biochars in 2% formic acid (FA-P), 2% citric acid (CA-P) and 1M neutral ammonium citrate (NAC-P). Fraction is the % of TP extracted. Standard deviation (n = 3) in parentheses. For FA-P, data from official method (FA-P, 30 min shaking only) and modified method (FAs-P, official method+10min sonication) are presented. ............................................................... 137 Table 6-4. Selected parameters of dry matter yields and P uptake by ryegrass fitted by the Mitscherlich equation ......................................................................................... 141 Table 7-1. Selected characteristics of feedstocks and biochars ................................... 161 Table 7-2. Estimated maximum release capacity (Qmax) of soil fertilised with different P sources (at T0) and estimated fast and slowly releasable P pools via a 2-component model. For Qfast, k1, Qslow and k2, left column are mean values and right standard errors. ....................................................................................................................... 169 XII LIST OF FIGURES Figure 2-1. New Zealand?s greenhouse gas emissions by sector: 2007. Source: Ministry for the Environment New Zealand (2009) ................................................................. 19 Figure 2-2. Overview of the sustainable biochar concept. Source: Woolf et al (2010) . 22 Figure 2-3. Schematics for biomass or biochar remaining after charring and decomposition in soil. Source: Lehmann et al (2006). .............................................. 23 Figure 2-4. Possible reaction paths and release mechanisms of S during devolatilization and combustion with special emphasis on combustion of annual. Source: Johansen et al (2011) ..................................................................................................................... 32 Figure 3-1. Solid state 13C DP-MAS-NMR spectra of biochars produced from biosolids- eucalyptus wood mixture (BSe) and cattle manure-eucalyptus wood mixture (MAe). (**) refers to spinning side bands. ............................................................................. 54 Figure 3-2. Plot of fa-measured (fa-exp) against atomic H/C ratios. Data were from literature (Table S3-1) and this study. 100% of aromaticity was set as 1 fa-unit....... 55 Figure 3-3. Comparison between fa-measured (fa-exp) and fa-predicted (fa-pre) obtained from different models.. ................................................................................ 55 Figure 4-1. The calibration curve used for correcting concentration of carbonate-C in biochars determined by a titration method. Oven-dried CaCO3 was used as a standard. ..................................................................................................................... 75 Figure 4-2. Examples of deconvolution of the derivative thermogravimetric (DTG) curves of biochars. The dark-filled peak of Sample EuW400 around 500?C represents the decomposition of whewellite (hydrated calcium oxalate). ................. 81 Figure 4-3. An overview of carbonate-C contents in biochars from literature and this study. The curve is the Normal curve representing the Normal distribution the data. ................................................................................................................................... 82 Figure 4-4. Effervescence tests for carbonate-C in biochars. Numbers are the samples numbers in Table 4-1. Sample ?No7x? is sample No. 7 after acid treatment; ?No 7x+? is ?No 7x? plus 5mg of dry CaCO3. ........................................................................... 82 Figure 4-5. Relationship between atomic H/total C ratio and fixed C/total C ratio. ...... 84 Figure 5-1. Correlation between hydrolysable N determined by difference between original biochar N content and residual N content and by alkaline potassium peroxodisulfate digestion. .......................................................................................... 97 Figure 5-2. Concentrations of different hydrolysable N forms by 6 M HCl hydrolysis. AN, ammonia-N; ASN, amino sugar-N; AAN, ?-Amino acid N and; UHN, unknown hydrolysable N. .......................................................................................................... 99 Figure 5-3. DTG curves of feedstocks and biochars and their residues after acid hydrolysis. ................................................................................................................ 102 Figure 5-4. Cumulative C mineralized on the basis of per unit of initial C. ................ 103 Figure 5-5. Extractable mineral N [ ?(NH4 + +NO3 ?)] change in a biochar-sand mixture system. All data were obtained by subtracting the values from the blank control. . 106 Figure 5-6. A modified C:N ratio for assessing net N mineralization or immobilization. VC, C fraction in volatile matter fraction; THN, total hydrolysable N by 6 M HCl hydrolysis. ................................................................................................................ 116 Figure 6-1. XRD spectra of biochars and biosolid feedstock (BSe-F). Possible struvite peaks in MAe were lined out by dotted lines; the region in the ellipse in BSe was attributed to?organic hump?. ................................................................................... 135 Figure 6-2. Shoot dry matter yield (a) and P uptake (b) from 6 harvests of ryegrass grown in pots of Waitarere sandy soil fertilised with feedstocks, biochars, and P fertilisers. In the same treatment, deeper colour indicated higher dose amendment. XIII Doses for biosolid biochars (BSe) are 2.5t ha?1 and 5t t ha?1; for manure biochars (MAe), 5 t ha?1 and 7.5 t ha?1; for phosphate rocks (SPR), 0.25, 0.5, 1 and 2 t ha?1; for calcium dihydrogen phosphate (CaP) , 100, 200, 800 kg ha?1. Error bars indicate standard deviations of experimental replicates (n=3). Different letters indicate statistically significant according to the S-N-K test at the 0.05 level. ..................... 138 Figure 6-3. Shoot dry matter yield of ryegrass grown in pots of Waitarere sandy soil fertilised with feedstocks, biochars, and P fertilisers at first 3 harvests (a) and first 6 harvests (b). Data were fitted by a Mitscherlich equation. Error bars indicate standard deviations of experimental replicates (n=3). ............................................................ 139 Figure 6-4. P uptake by ryegrass grown in pots of Waitarere sandy soil fertilised with feedstocks, biochars, and P fertilisers at first 3 harvests (a) and first 6 harvests (b). Data were fitted by a Mitscherlich equation. Error bars indicate standard deviations of experimental replicates (n=3). ............................................................................. 140 Figure 6-5. Relationship between dry matter yields and formic acid extractable P after sonication (FAs-P) (a), plant P uptake and extractable P concentration (b). Data were fitted by a Mitscherlich equation. Error bars indicate standard deviations of three experimental replicates (n=3). ................................................................................. 142 Figure 6-6. Relationship between P uptake predicted by the CaP model and measured P uptake using either FA-P (official method; shake for 30 min only) or FAs-P (modified method; 30 min shaking plus 10 min sonication) as the available P content. ................................................................................................................................. 144 Figure 7-1. Soil available P as tested by resin-P, Olsen P, oxalate P and total plant P uptake in soil amended with different P sources at T0 (after 21 days of equilibration with moist soil). ....................................................................................................... 163 Figure 7-2. Shoot dry matter yields and root dry weight of ryegrass grown in pots of Waitarere sandy soil fertilised with feedstocks, biochars, and conventional P fertilisers (mean ? std., n=3). Shoots (5 cm above soil surface) were harvested for 9 times successively. Means of shoot yields from 1-3 harvests, 4-6 harvests and 7-9 harvests, root weights and total biomass (shoot + root) were compared using one way ANOVA method. Values not sharing the same letter indicate a significant difference (Turkey HSD at a level of 0.05). Lower case was used for shoot yields of every 3 harvests and root weights; capital letters for total biomass. ....................... 164 Figure 7-3. P uptake of ryegrass grown in pots of Waitarere sandy soil fertilised with feedstocks, biochars, and conventional P fertilisers (mean ? std., n=3). Shoots (5 cm above soil surface) were harvested for 9 times successively. Means of shoot P contents from 1-3 harvests, 4-6 harvests and 7-9 harvests, root P content and total P uptake (shoot + root) were compared using one way ANOVA method. Values not sharing the same letter indicate a significant difference (Turkey HSD at a level of 0.05). Lower case was used for shoot P content of every 3 harvests and root P content; capital letters for total P uptake. ................................................................ 165 Figure 7-4. Extractable soil P in soils A) at T0 (after pre-equilibrating for 3 weeks but before sowing the seeds); B) at Th (after the separation of the root and soil) and; C) plant P uptake and difference in extractable P before and after plant growth. Values not sharing the same letter indicate a significant difference (Turkey HSD at a level of 0.05) (Figure 2A and 2B); (0.1), (*) and (**) denote a statistically significant difference with 0 at the P<0.1, P< 0.05 and P<0.01 according to Student?s t test (one- tailed). ...................................................................................................................... 166 Figure 7-5. Release pattern of P in soils fertilised with different P sources (at T0): A) Control and CaP; B) MAe; C): BSe and; D) SPR. For Control, CaP, MAe and BSe treatments, data were fitted via a 2-component model (Equations (7-3) and (7-4)) XIV after exploring the maximum release capacity according to Equation (7-2); data of SPR treatments were fitted by a linear model. Parameters are shown in Table 7-2. 168 Figure 7-6. Relationship between estimated Qmax-T0 and (Qmax-Th + total plant P uptake). .................................................................................................................... 170 Figure 7-7. Total plant P uptake as a function of extractable P of three successive resin extractions (at T0). Three successive resin extractions were chosen according to the amount of total plant P uptake. Data are mean of three replicates for P uptake and of two replicates for extractable P. The curve is the fit line of CaP data via a Mitscherlich-type modelling. ................................................................................... 174 XV ACRONYMS AN NH3 N AAN ?-amino acid N ASN Amino sugar-N BD Bloch-decay BSe A mixture of biosolids and eucalyptus wood chips C Carbon CaP Ca(H2PO4)2 C/N C to N ratio (mass) Corg Organic C DP/MAS Direct polarization/magic angle spinning Fa C aromaticity FC Fixed C DTG Derivative thermogravimetric analysis FC Fixed carbon H/C An atomic H to C ratio Horg Organic H H2SO4-P 0.5 M H2SO4 extractable P MAe A mixture of dairy manure and eucalyptus wood chips NaOH-Pi 0.1 M NaOH extractable inorganic P fraction NaOH-Po 0.1 M NaOH extractable organic P fraction NaOH-Pt total 0.1 M NaOH extractable P fraction N Nitrogen NMR Nuclear magnetic resonance P Phosphorus Pox Acid ammonium oxalate extractable P PSO Pseudo-second-order kinetic model PR or SPR Sechura phosphate rock SD Standard deviation TGA Thermogravimetric analysis THN Total hydrolysable nitrogen UHN uncharacterisable hydrolysable N VC Carbon in volatile matter VM Volatile matter