Figure shows the distributions of PDMA-metal complexation in the nutrient solution , under anoxic conditions at different pH values. We find that PDMA complexed only Zn II and Fe II in the pH range from 5 to 10. In this condition, almost 100 % of Zn II is complexed by PDMA from pH 6 to 9 and its complexation rapidly decreases above pH 9, whilst only the 30 % of Fe II is complexed by PDMA at pH between 7 and 10. This indicates that PDMA forms more stable complexes with Zn II (11.48) than with Fe II (9.11). In aerated solutions (Figure ), as in Figure , Cu II is already almost totally complexed at pH 4, Zn II and Fe III started to be complexed at pH 5, with 60 % of complexation for Zn II between pH 6.5 and 8, and 30% for Fe III from pH 6.5 to 10. Zn II complexation rapidly decreases above pH 8 highlighting a higher competition between iron and Zn II in alkaline pH. Suzuki et al. showed that in non-waterlogged soil conditions, the application of unchelated PDMA significantly increased the concentration of copper in plants. Only small amounts of manganese (Mn II : 0.0035% in Eh = 350 mV; 0.2% in Eh = -300 mV) and magnesium (Mg II : slightly above 0 % in both Eh = 350 mV and -300 mV) are complexed by PDMA in both redox conditions, in agreement with their low logK values. The varying PDMA speciation in the nutrient medium results in a different selectivity diagram for Zn II (log S; Figure and).