Interactions of fertilizer and chemical sanitizing agents in water

The objective was to quantify interactions between fertilizers and chemical sanitizing agents in nutrient solutions. Sodium hypochlorite, chlorine dioxide, and two commercial H₂O₂-based products were added to either NaCl at 385 mg L^‑1 or 17-1.8-14.1 at 100 mg L^‑1 N solutions, with and without iron-ethylenediaminetetraacetic acid (FeEDTA) at 1 mg L^‑1 Fe. The H₂O₂-based products did not decrease in active ingredient (AI) concentration. Chlorine dioxide and sodium hypochlorite decreased in AI more in the macronutrient solution than NaCl, but were not affected by FeEDTA. A second experiment evaluated interaction of Cu at 2 mg L^‑1 from either copper nitrate salt or copper ionization with different Fe-chelates [no chelate, FeEDTA, or iron-ethylenediamine-N,N’-bis (2-hydroxyphenylacetic acid) (FeEDDHA)], and solution pH levels (4.0, 5.5, 7.0, and 8.5) in a 17-1.8-14.1 nutrient solution at 100 mg L^‑1 N. Free Cu in the absence of Fe-chelate decreased when pH level was 8.5 compared with lower pH levels, particularly for Cu from copper salt. Copper reacted with Fe-chelates at all pH levels, presumably by substituting the chelated iron, and Cu from copper salt was less stable than copper ionization as free Cu. A third experiment evaluated the effect of all six sanitizing agents described above on concentration of FeEDTA and FeEDDHA. Copper from both salt and ionization sources at 2 mg L^‑1 Cu reduced the concentration of both FeEDTA and FeEDDHA, by 0.1 to 0.8 mg L^‑1 Fe after 1 h. The H₂O₂-based products decreased FeEDDHA concentration by up to 0.8 mg L^‑1 after 1 h and 1.3 mg L^‑1 after 24 h, but had less effect on FeEDTA (up to 0.3 mg L^‑1 decrease after 24 h). Chlorine dioxide at 0.5 mg L^‑1 and sodium hypochlorite at 2 mg L^‑1 did not affect Fe concentration from either chelate. Given the many complex reactions that occur, it is important to regularly measure sanitizing agent concentration under local irrigation conditions.