2. NUTRIENTS AND THEIR PROCESSES ) 1797 – 1734 Joseph Wright ( Joseph Wright by Phosphorus’ Phosphorus’ Nitrogen discovered by Daniel Rutherford in 1772 ’The Discovery of ’The Discovery Alchemist Hennig Brand 1699 1 Phosphorus (P) • Phos = light, phorus = bearer (Greek) • Apatite • 79% of mined P used for fertilizers • Other industry 11% • Food and feed 5% • Detergents 3% • Other 2% • Concentration in Earth’s crust 0.1% • Plants 0.3–0.4% DW • Humans 1.1% (about 700 g ind−1) http://phosphorusfutures.net/the-phosphorus-challenge/the-story-of-phosphorus-8-reasons-why-we-need-to-rethink-the-management-of- phosphorus-resources-in-the-global-food-system/ 2 Do we get too much P in diet? 1884/ - phosphorus - of - syrup - http://skittishlibrary.co.uk/freemans An English advertisement in 1884 3 Nitrogen (N) • No major geological source • Concentration in Earth’s crust 0.002% • Synthesis of ammonia (Fritz Haber, Nobel 1918) N2+ 3 H2↔ 2 NH3 – Requires a lot of energy • Production of ’reactive N’ – 1860: 15 Tg y–1 N – 1990: 156 Tg y–1 N – More than 100 Tg y–1 N in fertilizers • Plants <2% DW – + – Plants take up NO3 and NH4 • Humans 2.6 % 4 Nitrogen fertilizers and world population Sutton et al. (2011) 5 Apatite mineral – – – 2– Ca10(X)(PO4)6, X = 2OH , 2F , 2Cl , CO3 απατείν (apatein, Greek) = to deceive or to be misleading - desert 1. Magmatic apatite - – Russia, Finland, South Africa, Zimbabwe, Brazil – Weak fertilizer value as such, mycorrhizae can solubilize to small extent – Finnish (young) soils contain a high concentration of apatite Wkipedia + Apatity, Russia / 2. Sedimentary apatite – 80% of production world/508853 – USA (Florida), Morocco, China - the – Higher reactivity - – Cd, U feeds - that - rock Western Sahara https://www.theatlantic.com/science/archive/2016/11/the 6 Phosphoric acid and its anions Orthophosphoric acid • Weak triprotic acid O + − H3PO4 ↔ H + H2PO4 (pKa = 2.12) − + 2− − − H2PO4 ↔ H + HPO4 (pKa = 7.21) O P O 2− + 3− HPO4 ↔ H + PO4 (pKa = 12.67) O− Anion of phosphoric acid = dissolved orthophosphate • The only P-compound that ubiquitously can pass the cell wall, that is the only directly available P form • Highly reactive 7 Other P-compounds Phosphate can be condensed: O O Bind with an organyl group: − O− P O P O O O− O− Pyrophosphate OH P O R O O O OH − P P − Na+ Phosphate monoester (P–O–C) O P O O O • E.g. phytic acid • Weakly hydrolysable O− O− O− 5 O Sodiumtripolyphosphate R1 O P O R2 Form P–C bonds: O O H OH HO P C N C C Phosphate diester (C–O–P–O–C) • E.g. nucleotides and HO OH phospholipides • Easily hydrolysable Glyphosate – a phosphonate 8 Phytic acid (myo-inositol hexakis phosphoric acid) • Salts of phytic acid: phytates • Storage form of P in bran and seeds • Stable, weakly hydrolysable monoester • Fungi can exrete phytase and utilise inositol P • Nonruminants cannot utilise, only rumen microorganism produce phytase • Can be bound to same sorption sites as orhophosphate Wikipedia 9 Phosphates in detergents • Sodium tripolyphosphate (Na5P3O10) – Chelates Ca2+ and Mg2+, which would react with surfactants, ”water softener” – Used to be as much as 40% of ingredients – Hydrolyses easily to orthophosphate • EU regulation – No phosphate in laundry detergents for consumer use after 30.6.2013 – No phosphate in dish machine detergents for consumer use after 1.1.2017 • Phosphate replaced by zeolite, citrate, polycarboxylates, phosphonates • SCOPE Newsletter – http://phosphorusplatform.eu/ 10 Phosphorus fertilizers Superphosphate • Solubilisation of P in bones and apatite by sulphuric acid Ca(H2PO4)2 • Patented in 1842 • Industrial manufacturing began in Suffolk(UK) in 1847 South American nitrates • NaNO3, Ca(NO3)2 Bone Triplesuperphosphate • Replaced guano • In 1960s • Solubility of P increased by acid in early • Phosphoric acid + 1800s apatite Guano (N, P, K) • Incas used before colonisation • Peruvian guano exported to USA and UK in 1840s Ashley et al. (2011) 11 Ancient P sources Guano mine in Peru in about 1860 (Wikipedia) Skulls of bisons for manufacturing fertilizers in 1870s (https://rarehistoricalphotos.com/bison-skulls-pile-used-fertilizer-1870/) 12 Future P sources? • Mineable P reserves will last for 40–400–X years • China forbade P export in 2008, price of rock P increased by 700% • EU has defined P as a critical raw material ”Trilemma” (Obersteiner et al. 2013) 1. Rich P consumers • Use too much P • Try to secure import 2. Poor and food unsecure P consumers • 30% cultivated land suffers from P deficiency 3. P producers • Known reserves: Morocco 75%, China 6%, Algeria 3.3 %, Syria 2.7 %, South Africa 2.2 %, Russia 1.9%, Jordan 1.9%, USA 1.6% (USGS 2015) • Try to control the price of P • High price would secure P reserves but cause problems for the developing countries P reserves should be known better, P should be used in moderation and recycled 13 Siilinjärvi open mine – The only phosphate mine in western Europe 14 14 Gypsum heap in Siilinjärvi (CaSO4 ∙ 2H2O) Ca5(PO4)3X + 5 H2SO4 + 10 H2O → 3 H3PO4 + 5 CaSO4 · 2 H2O + HX 15 15 Soil particles are negatively charged… + + + + + + + + + + + + - - - - - - - - - - - - - - - - + + + + + + + + + + + - - - - + + + + + - - - - + + 16 2− O2 [0] [−] Isomorphic substitution Si4+ Al3+ Silicon tetrahedron …due to isomorphic substitution [0] [−] Isomorphic substitution Al3+ Mg2+ 17 Aluminium octahedron 17 Recap I • What is apatite? – – – 2– – Ca10(X)(PO4)6, X = 2OH , 2F , 2Cl , CO3 • Orthophosphoric acid? – H3PO4 • Dissolved orthophosphate? − 2− 3− – H2PO4 , HPO4 , PO4 • Why it is important? – Only P-compound that passes the cell wall • What is the charge of soil particles? – Mostly negative 18 Iron and aluminium oxides • Aluminium 3rd commonest element in Earth crust (8%) • Iron 4th commonest (5%) • Weathering produces Fe and Al hydroxides, oxyhydroxides, hydrated oxides, poorly crystalline oxides, amorphous oxides, sesquioxides.. • Charge depends on pH, positive at low pH +2 0 −2 Al Al Al O OH2 O OH O O −2H+ −2H+ Al +2H+ Al +2H+ Al O OH2 O OH O O Al Al Al Picture: Hartikainen (2017, Modified) 19 Sorption-desorption reactions Weathering Fertilizers, manure, Plants take up P sewage sludge… dissolved in soil solution P P P in soil solution P in soil solution (< 1% total P in soil) P in soil solution would not be enough for plants without P exchange between soil solution and soil particles P P P P <—Labile P pool—> P P P P P P P P P P P ||||||||||||||||||||||||||||| ||||||||||||||||||||||||||||| Fe and Al oxides Fe and Al oxides P P ”Aging” 20 Apatite, humic-bound P <—Stabile P pool—> Apatite, humic-bound P 20 Binding of anions • An electrostatic repulsion between a negatively charged soil particle and a negatively charged anion • Unspecific binding – Possible to positive surfaces, which only occur in Finland under very acidic conditions • Spesific binding – Spesific ligand exchange reaction (Hingston et al. 1967) • Some anions can bind chemically to the central cation of Al and Fe oxides – Charge of Al and Fe oxides depend on the pH − − – Anion (e.g. H2PO4 ) replaces H2O or OH group and binds by its O2 to the central cation Binding tendency of anions − − 2− − − Anion of the OH H2PO4 SO4 Cl NO3 acid Hydroxide > Phosphate >> Sulfate > Chloride = Nitrate Acid H2O H3PO4 H2SO4 HCl HNO3 Central cation can be compared to H+ Acids donate H+ the more eagerly the stronger the acid The stronger the acid, the weaker the corresponding base Weak base does not take H+ or bind to central cation 21 Picture: Hartikainen (2009) Picture:Hartikainen Phosphate binding Negative tendency charge increases decreases binding upon binding of an anion to - > Al oxide With lowering pH the surface charge of oxides becomes more positive -> binding tendency increases as the electrostatic repulsion decreases and H2O group is more easily replaced than OH 22 Sorption desorption reactions are not fully reversible • Sorption initially fast (min, h), followed by a slow reaction (d) • Binding may first occur binuclearly, i.e. anion is bound to two central cations • With the increase in anion saturation, binding becomes monodental and weaker • In time, binding may become stronger – Binding is changed from monodental to bidental – Adsorption is followed by absorption (P is diffused into a soil particle) – Adsorbed P is covered by Al ja Fe oxides (occlusion) • In addition to sorption, secondary P minerals may be formed, if concentrations exceed solubility product, e.g. after fertilising 23 23 Characteristics affecting P binding Sorption promoted Desorption promoted Sorptive components Plenty Little Saturation of sorptive components Low High Ionic strength High Low Competing anions Little Plenty pH Low High 24 Development of soil P reserves over time = Apatite = Fe-P, Al-P, (Ca-P) 25 An example on vertical P stratification in a cultivated soil Ap horizon • Plough layer • Enriched with P • P mainly as secondary P forms and organic P • Degree of P saturation: 8–36% • Source of dissolved P ”Al-P” B horizon • Apatitic P weathered and ”Fe-P” transformed to secondary P ”Ca-P” forms • Degree of P saturation: <7% • Sink for dissolved P C horizon • Apatitic P dominates Peltovuori (2006) 26 Phosphorus determination 27 27 Operational P forms • DRP ≠ dissolved orthophosphate!! – In acid conditions labile esters and polyphosphates will be hydrolysed – Complexes between phosphate and metals will be degraded – Colloidal metal oxides will be dissolved – Silicate, germanium and arsenate interfere with the determination • DUP – P forms that go through the filter, but require digestion to react with molybdate – e.g.