simulating the addition of these metals as part of a mineral fertilisation. Tables summarise this data. All data in this section are the results of simulations modelled in PHREEQC, adding PDMA as free ligand (concentration of 10 -6 M) in 0.1 M NaCl solution in waterlogged (Eh = -300 mV) and oxygenated (Eh = +350 mV) conditions. Metal ratios were based on the average concentration of Zn II , Cu II and Fe III present in soil . The pH used for the models were chosen to represent acidic, neutral, and alkaline soils to cover the range of pH conditions found across different paddy soils. Fe II is not included in the tables because no complex formation with PDMA occurs, due to its lower logK value compared with Zn II and Cu II . Under Zn II fertilization (Table ), at low Eh values (waterlogged soil), [Zn(PDMA)] -is the predominant complex particularly at pH 7 and 9; even when the concentration of Zn II is lower than Cu II and Fe III , [Zn(PDMA)] -complex represents 10%. As explained before, in this condition copper and iron are mainly present in their reduced forms with lower affinity (logK) for PDMA compared to Zn II , and for that reason there is no competition. At high oxidizing conditions (aerated soil), [Cu(PDMA)] -is the predominant complex; whilst [Zn(PDMA)] -slightly increases from 0 to 2% as consequence of increasing concentration in soil, particularly at pH 7 and 9. Based on logK values, in this condition we expected that iron, present as Fe III , should be preferred by PDMA relative to Zn II and Cu II . Nevertheless, [Cu(PDMA)] -is the dominant complex in all the tested conditions, ranging from 95 to 100% of formation. This is probably because at sub-acidic pH, iron is present in its divalent form in both the tested Eh conditions , and cannot compete with Zn II and Cu II for the PDMA complexation; whilst at high pH iron precipitates as Fe2O3 , becoming less bioavailable.