Table 1 Examples for the observations reported for the competitive sorption and complexation reactions between organic matter (OM) and phosphate ions (P)
Reactions | Forms and origin of OM | Observations | References |
|---|---|---|---|
Competitive sorption | |||
 Organic matter (i.e., dissolved OM and OM fractions, such as fulvic and humic acids) inhibits P sorption in soils | Dissolved organic matter (DOM) derived from green manure, poultry manure and cattle manure | P sorption was only inhibited by DOM derived from green manure in the order of citric acids > clover vetch  • Citric acids and clover vetch can react with soil Al through ligand exchange reactions  • DOM derived from animal manure has a higher molecular weight, which is not able to react with soil Al | [60] |
DOM derived from crop residues, animal manure and composts | Pre-adsorbed DOM onto mineral adsorption sites decreased P adsorption by 19%, but did not increase plant-available P Only aromatic molecules > 600 Da in DOM competed with P for mineral adsorption sites | [12] | |
DOM extracted from fresh and decomposed agricultural residues | Addition of decomposed DOM decreased P sorption onto goethite, gibbsite and kaolin more than DOM derived from fresh OM The DOM adsorbed in the order of amorphous Al compounds > amorphous Fe compounds > goethite | [38] | |
Fulvic acids (FA) derived from decomposing OM | Addition of FA decreased in the P sorption in three of the four soils | [35] | |
Humic acids (HA) derived from soil | Addition of HA significantly decreased P adsorption onto goethite up to 28% | [20] | |
Commercial HA, which contain negligible amount of total P and 36.7 g kg−1 carbon | Addition of HA inhibited the P adsorption in black soils | [100] | |
 Organic matter (i.e., dissolved OM and OM fractions, such as fulvic and humic acids) increases P sorption in soils | DOM derived from leachate from incubated soybean and Rhodes grass hay (decomposed OM) | Addition of DOM decreased the P sorption after 1.5 h but increased P sorption in Oxisols after 6 d | [35] |
SOM in top soils was chemically removed by H2O2 | The removal of SOM from topsoil resulted in a decrease in the P sorption capacity in sandy soils | [14] | |
Competitive complexation | |||
 Formation of binary complexes:   Preferrable formation of OM–Fe(III) complex over Fe–P mineral formation | Leonardite HA | Formation of Fe–P precipitation was inhibited in the presence of HA | [71] |
Aquatic OM (Suwannee River natural OM) | Stable Fe(III)-OM binary complexes prevented reaction with P and strongly suppressed the formation of Fe–P minerals (FePO4), the ternary OM–Fe–P complex as well as Fe(III) hydroxides | [84] | |
  DOM inhibits CaP precipitation and transformation | HA | Formation of Ca–P precipitates was slower in the presence of HA HA strongly stabilized amorphous CaP (ACP) delaying the transformation to thermodynamically more stable phases | [22] |
 Formation of ternary complexes:   Formation of OM–Ca–P complexes | Organic and mineral soil layers in four calcareous forest soil profiles | The colloidal P was originated from the overlying organic soil horizons and Ca2+ drove the formation of ternary SOM–Ca–P complex | [93] |
HA derived from calcareous and muck (organic) soils | Ca2+ preferentially complexed with HA over forming Ca–P minerals Formation of ternary HA–Ca–P complex depends on soil pH and the structures of HA | [4] | |
Natural organic matter (NOM) derived from Suwannee Rover, Nordic Lake and Pony Lake | Ca–P precipitation was enhanced in the presence of NOM in the electrochemical P recovery system Transformation of ACP to stable Ca–P mineral form was delayed | [44] | |
Development of organic complexed superphosphates (CSP) | Organically complexed superphosphate (CSP), i.e., monocalcium phosphate complexed by the organic chelating agent through Ca bridges, was more efficient than super phosphate in providing available P for wheat plants due to the ability of CSP to inhibit P fixation in soil | ||
  Formation of OM–Al(Fe)–P complexes | Humus soil samples from two groundwater discharge areas, which contain high native amounts of Al and Fe | The accumulation of Al and Fe in humic soils increased P sorption capacity by forming OM–Al(Fe)–P complexes | [29] |
HA derived from soil | Formation of HA–Al–P, but not with Fe in acidic agricultural mineral soil (pH 5.4) was observed The binding of organic P to HA does not involve either Fe or Al bridges | [8] | |
HA and ferrihydrite (FH) | Complexation of FH–HA–P depended on pH and ionic strength The adsorption of P decreased with increasing ionic strength at pH < 7.5, while it increased with ionic strength at pH > 7.5 HA retarded the reduction rate of P adsorption onto the FH–HA complexes | [91] | |
Metal–organic frameworks prepared with Fe and terephthalic acid (H2BDC) | Fe-based metal–organic frameworks (MOF) incorporated P forming OM–Fe–P complexes in eutrophic water samples Fe-based MOF exhibited a higher selectivity towards P over Cl−, Br−, NO3− and SO42− | [98] | |