Rice is cultivated in a wide range of soil conditions, with pH ranging from 4 to 9, redox potential (Eh) ranging from 700 to -300 mV, related to aerated and waterlogged conditions, and ionic strengths typically ranging from 0.02 M to 0.16 M . Other cationic micronutrients like Fe II /Fe III , Cu II , Ni II , Mn II , Mg , and Co II are present in agricultural soils, with their concentrations depending greatly on the composition of soil parent material and on anthropogenic activities (i.e. fertilizer addition to the soil surface) . These micronutrients have several cellular functions and consequently play important roles in plant growth. The relative concentration ratios of these metal ions need to be kept at an optimal range to fulfil their biological functions. Therefore, if a chelator such as PDMA is to be used as potential fertilizer to enrich the amount of zinc taken up by plants, it is essential to understand the interplay between this ligand and the different metal ions to prevent unwanted competition between ions. The aim of this work is to investigate if PDMA can be effectively used as Zn II fertilizer in paddy soil and to establish under what soil conditions. To this end, we determined the stability constants of PDMA with Zn II and competitor ions, i.e., Fe II /Fe III , Cu II , Co II , Ni II , Mg II , and Mn II in 0.15 M NaCl solutions. We performed a wide variety of aqueous geochemical calculations to determine the speciation of metal-PDMA complexes in saline and representative soil solutions across a range of pH, ionic strengths, and redox conditions relevant to the rice paddy soil environment. This enabled us to determine a selectivity index for Zn II -PDMA complex and hence to identify soil conditions conducive to preferential formation of Zn-PDMA complexes over other metal complexes. Finally, we used a recent study testing the potential of PDMA as iron fertilizer by Suzuki et al. to validate our model calculations.