Our final objective was to identify the conditions for a successful application of PDMA as Zn II fertilizer in the presence of competing cations. To this end, we modelled the % formation of metal-PDMA complexes (for Zn II , Cu II and Fe III ) formed with excess Zn II and the percentage reduction of [Zn(PDMA)] -complex in presence of excess Cu II and Fe III , i.e.