Foliar Applications of Humic Substances Together with Fe/Nano Fe to Increase the Iron Content and Growth Parameters of Spinach (Spinacia oleracea L.)

Iron deficiency, which severely decreases the plant yield and quality, is one of major problems calcareous soils. Foliar applications humic substances and/or Fe fertilizers are environmentally friendly methods to cope with deficiency. The aim this study was investigate combined effect Fe/nano humic/fulvic acid-based biostimulant foliar on content growth parameters spinach. Treatment solutions were prepared either by mixing a common fertilizer, FeSO4·7H2O, different commercial biostimulants (Fulvic-based: Fulvagra®, Fulvagra®WSG; Humic-based: HS300®, Humin Fe® Liqhumus®, Grevenbroich, Germany) or nano ferrihydrite ratios fulvic substance (FA-50, FA-75, FA-100) acid (Nano Iron). Growth (plant fresh dry weights, matter, root leaf number per plant, area); chlorophyll reading value (SPAD); (a,b, total) carotenoid contents; mineral contents (N, P, K, Ca, Mg, S, Cu, Mn, Zn, B, active Fe, total Fe) samples determined. Our results showed that application together sources improved nutrient uptake, contents, characteristics, yield; however, not all had same effect. When considered, Fulvagra treatment—which contained 17% microorganisms in its 20 mM FeSO4·7H2O—was most effective application, followed FA100 treatment containing ferrihydrite. This finding indicates more than humic-based against deficiency due their low molecular weight enables better penetration into leaves. In conclusion, can be used increase uptake crops yields under Fe-deficient conditions.