Chemical Reactions of Polyphosphate Fertilisers in Soils and Solutions Thérèse McBeath In fulfilment of the requirements for the degree of I)octor of Philosophy A thesis submitted to Soil and Land SYstems School of Earth and Environmental Sciences The UniversitY of Adelaide Australia July 2006 Table of Gontents Table of Contents II List of Figures VI List of Tables IX Acknowledgements XI Abbreviations XIII Abstract XIV Declaration XVI Crr¡,PrNN 1. GNNAN¡T, IXTNONUCUON ÀND LITERÄTURE TIEYIEW 17 1.1. Introduction t7 I.2. Phosphorus in the Environment and Agriculture 18 1.2.1. Phosphorus sPecies in soil t9 1.3. Phosphorus Fertilisers 22 1.4. Reactions of P in Soil 25 1.4.1. Chemical Reactions 25 1.4.2. EnzymaticReactions 29 1.5. Factors Controlling P Availability in Soils 32 1.5.1. Soil pH 32 1.5.2. Iron and Aluminium 33 1.5.3. Calcium 39 1.5.4. Organic Residues and Micro-organisms 45 1.6. Reactions of P Fertiliser in Soils and Solution 48 1.6.I. Orthophosphate FertiliserDissolution 48 1.6.2. Poþhosphate Fertiliser Hydrolysis in Soils and Solutions 51 1.7. Movement of P in Soils 54 1.8. Conclusions and Future Direction 58 CHAPTER 2. POLYPHOSPHÄTE SPNCT¿,TTOU TX SOT,UTTOU 6l 2.1. Introduction 6l 2.2. Materials and Methods 63 2.2.L. On-lineColorimetrY 63 2.2.2. Ion ChromatograPhY 64 2.2.3. PhosphateReagents 65 2.2.4. Performance of the Analytical Techniques 66 2.3. Results and Discussion 69 2.3.1. Performance of the Analytical Methods 69 2.4. Conclusions 74 cu¡prnn 3. Por,ypnospHlTn Fnnrn-rsnn sor-urro¡l sr¡,srr,rrv 75 3.1. Introduction 75 3.2. Materials and Methods 77 3.2.1. Reagents 77 3.2.2. Treatments 77 3.2.3. Speciation and Quantification of P 77 3.2.4. StatisticalAnalysis 78 3.2.5. Calculations 78 3.3. Results and Discussion 79 3.3.1. Change in P Speciation Over One Month 79 il 3.3.2. Hydrolysis Rate Constant 80 3.3.3. Activation EnergY 82 3.3.4. Change In P speciation Over One'Week 83 3.4. Conclusions 85 SOTT-: A CHAPTER 4. HYONOT,YSIS OF PYNOPTTOSPHATE IN A IIIGIil,Y CIT-C^MNOUS sor,ro-Sr¡.Tn 3tP NMR Sru¡Y. 86 4.I. Statement of Contributions 86 4.2. Introduction 87 4.3. Materials and Methods 88 4.3.1. Soil Collection and Chemical Properties 88 4.3.2. Soillncubations 89 4.3.3. Solid-State'lP NMR Spectroscopy 89 4.3.4. Ion ChromatograPhY 9T 4.4. Results and Discussion 92 3tP 4.4.1. Solid-State NMR Spectra of Reference Salts 92 4.4.2. Solid-State'rP NMR Spectra of Soils 94 4.4.3. of orthophosphate and Pyrophosphate contents Quantification 3tP from Solid-State NMR SPectra 97 4.4.4. Quantification of Orthophosphate and Pyrophosphate Concentrations Using Alkaline Extraction and Ion Chromatography 99 4.4.5. Hydrolysis Rate and Pyrophosphate Half-Life 100 4.5. Conclusions 102 103 Crr¡,PrPN 5. SORPTION OF PYROPHOSPIIATE AND ORTHOPHOSPIIATE NI SOTT- 5.1. Introduction 103 5.2. Materials and Methods 104 5.2.I. Reagents 104 5.2.2. Soil Types and Characteristics 104 5.2.3. Soil Analyses 105 5.2.4. Speciation and Quantification of P 106 5.2.5. SorPtionCharacteristics 106 5.2.6. StatisticalAnalysis t07 5.3. Results and Discussion 108 5.3.1. Soil Characteristics 108 5.3.2. SorptionCharacteristics 108 5.3.3. pH 116 5.3.4. CationConcentrations tl7 5.3.5. Organic Carbon t20 5.4. Conclusions t22 Cr¡1¡prBn 6. IS9TOPIC TnCrn¡rQupS ron I¡.IVESTIGATING REACTI9NS OF 123 PoLYPHOSPHATE tr'ERTtr,ISERS IN SOILS 6.1. Introduction t23 6.2. Assumptions and Principles of Isotopic Techniques t24 6.2.1. TracerTechniques t24 6.2.2. Isotopic DilutionTechniques 125 6.3. Double Labelling Techniques 126 6.4. IsotopicExperiments t28 6.4.1. The Processes Under Investigation t28 6.4.2. Chapter 7- A Hydrolysis Study t29 ilI 6.4.3. Chapter 8- A Lability StudY 130 6.4.4. Chapter 9- A Mobilisation Study 130 6.5. Conclusions 131 Culprnn 7. AN ISOroprC SrUoy or PynopnoSPHATE HYDRoLYSIS 132 7.1. Introduction t32 7.2. Materials and Methods t33 7.2.1. Soil Characteristics 133 7.2.2. Reagents 133 7.2.3. ExperimentalDesign t33 7.2.4. AnalyticalMethods t34 7.2.5. Calculations 135 7.2.6. StatisticalAnalysis 138 7.3. Results and Discussion 138 7.3.1. Examination of Isotopic Exchangeability of Phosphorus in Pyrophosphate 138 7.3.2. Effect of Rate of Pyrophosphate Added on Soluble Phosphorus Concentration and Soil Suspension pH 139 7.3.3. Effect of Rate of PP Added on Lability and Hydrolysis of PP t42 7.4. Conclusions 145 CTHPTNN 8. A STUOY OF LABILITY OT P TN SOTT,S TREATED WITH ONTTTOPTTOSPHATE ANDPYROPHOSPHATE 146 8.1. Introduction 146 8.2. Materials and Methods 147 8.2.1. Soil Characteristics 147 8.2.2. Reagents 148 8.2.3. Experimental Design 148 8.2.4. Analytical Methods 149 8.2.5. Calculations 149 8.2.6. Statistical AnalYsis I52 8.3. Results and Discussion 152 8.3.1. Incubation Effects on Soluble Phosphorus, PH, Cations and Organic carbon 152 8.3.2. Incubation Effects on Lability and Partitioning of Orthophosphate Compared to PyroPhosPhate 159 g.4. Conclusions . 163 CHÄPTER 9. MOBTLISATION OF NITTVN PHOSPHORUS NY PYNOPHOSPIIATE 165 9.I. Introduction 165 9.2. Materials andMethods t66 9.2.1. SoilCharacteristics r66 9.2.2. Reagents r66 9.2.3. ExperimentalDesign t66 9.2.4. Analytical Methods t67 9.2.5. Calculations t67 9.3. Results and Discussion 17t 9.3.1. Effect of Pyrophosphate Addition on soluble Phosphorus Concentration and Soil Suspension pH t7I g.3.2. Labile Pyrophosphate, Labile Hydrolysed Pyrophosphate and Mobilised Native PhosPhorus 172 IV 9.4. Conclusions 177 Cn¡,prnn 10. Gnxnnlr, DrscussroN 179 10.1. Summary of Findings r79 10.1.1. Analytical Techniques t79 10.I.2. Hydrolysis in Solution 180 10.1.3. Hydrolysis in Soil 180 10.1.4. Sorption 180 10.1.5. Isotopic Studies of Lability, Hydrolysis and Partitioning 18r 10.1.6. Fate and Effects of PP Reactions in Soils t82 10.2. Future Research 18s Rrrpnpxcns 187 V List of Figures Figure 1-1: The P cycle in soils. The boxes represent pools of P forms in the cycle and affows represent movement and transformations between pools (Burns and Slater te82)..... Figure 1-2: Phosphorus rate (ky'ha) vs. grain yield (t/ha) for ammonium @'T:: ::l*i::::T i:::lï:".'lï::l":lï:P :T:*:: ?' :', 7?i?; Figure 1-3: Common ions of P in pollphosphate fertilisers (Rashchi and Finch 2000) Figure 1-4: Covalent bonding reactions of P (Stevenson and Cole 1999).-.-.......-.......27 Figure 1-5: Electrostatic attraction reactions of P with Fe (Stevenson and Cole 1999) Figure 1-6: Effect of pH on enzyme activity (corn-root acid phosphatase and pyrophosphatase activity). Acid phosphatase activity is expressed as pg p- nitrophenol released/l0 mg corn rootslhr, and pyrophosphatase activity is expressed as ¡rg Pi released/l0 mg corn roots/hr (Gilliam and Sample 1968). ...31 Figure 1-7: Ionic forms of P in soil solution as a function of pH (Brady and'Weil, lee6) .32 Figure 1-8: The effect of pH on the P species in soil solution (Lindsay 1979)...........34 Figure 1-9: Precipitates of Fe and Al (Brady and V/eil 1996)- ....'........-....36 Figure 1-10: Solubility diagram for Al phosphates (Lindsay et al. 1962)...................37 Figure 1-11: Solubility of Ca phosphates compared to strengite and variscite (Lindsay 1979). --..-..42 Figure 1-12: OP concentration (0.00lM) as a function of time (hour) for three OP solutions reacted with calcium carbonate with and without Na-PP (Amer and Mostafa 1981). 44 Figure 1-13: Interactions of organic P in soils (Stevenson and Cole 1999). ...............47 Figure 1-14: Hydrolysis of 50ppm P as PP and TP solutions (measured as OP formed) by sterile and non-sterile wheat and pea roots (Savant and Racz I97 2).............. 5 3 Figure 1-15: Movement of phosphate by mass flow and diffusion from a granule of triple or single superphosphate through water-filled and water-lined large micro- pores in a well aggregated soil. Penetration of P into aggregates is incomplete due to the slow rate of P diffusion in smaller intra- aggregate micropores and discontinuous micropores (Hedley and Mclaugþlin 2005) 56 Figure 2-l: Calibration curves for anaþsis of P species by the on-line colorimetric technique. (A) OP (50.0034x, Rz:l) andby IC (B)OP (52'19x, R2:l), PP (y:2.04x, R':t) utrã tp (y:2.15x,R2:1). *Error bars repres ent -rl- standard effor.. 70 Figure 3-l: Percentage of P species as OP, PP and TP after one day at4"C and after 28 days aI4"C,25"C and 50oC. Measurements were made at solution pH values of 6.4,5.8,4.9 and2.3. .. 80 Figure 3-2 Change in log TP concentration (mg/L) over time (hours) at4"C,25"C and 50'C (-0-50'C -t-25"C -A-4'C) at soh'tion p}J6.4. The equation of the line at 4"C is y: 2xl0-e +3.997 with a R2 of 0'03 I, at 25" C p3x1'0-8+3.99 with a R2 of 0.49, andat 50'C 5-4x10-7+4.04 with an R' of 1..81 Figure 3-3: Change in 1og TP concentration (mg/L) over time (hours) at pH 2.3,4.9, 5.8 and 6.4 (r-pH 2.3 -'-pH 4.9 - L-pH5.8 -r--pH 6.4) at25"C.