Preparation of the treatments
PDMA was synthesized and supplied by the Aichi Steel Corp. (Japan) as
described in a previous report (Suzuki et al., 2021). The PDMA–Fe
complex was prepared as described in a recent work (Ueno et al., 2021).
First, we mixed 2.47 M FeCl3 with 10 mM PDMA at a ratio
of 2:1 and then adjusted the pH to 7.0 with 0.5 M NaOH. Next, the
solution was incubated for 1 h at 50°C and centrifuged for 3 min at
15,000 rpm. Finally, the mixture was filtered with a 0.22 µm syringe
filter. The PDMA and PDMA–Fe were stored at −20°C until use. EDTA–Fe
(CAS No. 15708-41-5; Shanghai Macklin Biochemical Co., Ltd., China) was
used as a positive control in the pot and field experiments.