Iron-Humate as a Source of Iron for Plants

Abstract

An investigation in three replications was conducted to study the release and diffusion of iron (Fe) from iron-humate (Fe-HA) chelates and to assess its availability to growing plants. Labeled, 59Fe-HA, chelates, contained in dialysis bags, were dialyzed against distilled water, a Hoagland nutrient solution, a solution of 10−4 ethylenediamine tetraacetic acid (EDTA) or diethylenetriamine pentaacetic acid (DTPA), and 10−4 M citric acid, and the amount of radiation in the respective solutions measured at 1, 4, and 14 days after dialysis. Assessment of plant uptake of chelated 59Fe-HA and transport of Fe from root to leaf-tissue were examined by growing plant seedlings in Hoagland solutions for 30 days. The Fe source was labeled 59Fe-HA chelates, contained in dialysis bags, placed in the nutrient solutions, treated with or without EDTA. Since different plants were believed to exhibit different mechanisms, called strategies, in absorption and transport of Fe, two types of plants were grown, sunflower and barley plants, representing plants with strategy I and II, respectively. At the end of the growing period, roots, and leaves were sampled, dried, and ground for radiation analysis by the solid scintillation method. The results of diffusion analyses with 59Fe indicated that no diffusion of Fe has occurred from the dialysis bags into the distilled water or Hoagland solutions. Only in the presence of EDTA and DTPA was chelated Fe released by ligand exchange and transported as Fe-EDTA or Fe-DTPA into the outside solutions. Although the results of plant experiments indicate that both types of plants used are capable in absorbing Fe from the HA-Fe source, sunflower (strategy I) roots were apparently more efficient in the transport of Fe from the source to the roots than barley plants (strategy II). However, barley plants, conforming to the strategy II concept, seemed to promote Fe transport from root to leaf-tissue better than sunflower roots.