Magnetic iron oxide nanoparticles in humic substances shell - Fe3-delta O4@HS were synthesized by oxidative in situ method in aqueous solutions of humic substances from metallic iron precursor. Humic substances interacting with metallic iron under natural conditions act as a complex reagent that participates in acid-base, redox, complexation reactions and adsorption processes. The Fe3-delta O4@HS particles is the final product of corrosion of metallic iron in the presence of HS. Products were characterized by dynamic light scattering, scanning and transmission electron microscopy, X-ray powder diffraction, Mossbauer spectroscopy, magnetometry, infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and evolved gas analysis. It was demonstrated that the samples contained particles with sizes of 40-50 nm comprised of similar to 24 nm magnetite-like crystalline cores coated by humic substances. The synthetic approach used in this article can be used as a model of corrosion processes of ferrous metals in nature. In addition, magnetite-like nanoparticulates stabilized with humic substances can be promising as bioavailable iron additives for agricultural applications.Magnetic iron oxide nanoparticles for agricultural applications can be obtained by the simple interaction of metallic iron with aqueous solutions of humic substances.