Potential foliar fertilizers with copper and zinc dual micronutrients in nanocrystal suspension

Control preparation, aqueous stability, and ion release of several Cu-Zn-containing crystals in suspensions have been investigated as potential dual micronutrient foliar fertilizers. These crystals were prepared by quick co-precipitation through simultaneously adding potassium hydroxide and copper salt solutions into zinc salt solution, and characterized in structure and composition with XRD, FTIR, SEM, TEM, and ICP in detail. As-prepared Cu-Zn mixed hydroxide nitrate was identified as a two-phase mixture while Cu-Zn mixed hydroxide sulfate as a single-phase compound. These crystals are all sheet-like in morphology and stable in aqueous solutions with pH 5-9. No phase change was detected after the samples were kept in shelf for >3 months, suggesting that these crystals have long shelf lives. In terms of ion release, Cu-Zn mixed hydroxide nitrate and Cu-Zn mixed hydroxide sulfate can afford similar to 4 and similar to 1 mg L-1 of Cu2+, respectively, which could be suitable for different levels of copper deficiency in plants. Moreover, both compounds can provide 38-39 mg L-1 of Zn2+ in aqueous suspensions. Thus, our findings suggest that as-prepared compounds can be potentially applied as long-term foliar fertilizers to simultaneously correct deficiencies of copper and zinc in various crops.