18th International Symposium on Iron Nutrition and Interaction in Plants
Madrid – May 30-June 3 2016
KINETICS EFFECTS OF LEONARDITE IRON FERTILIZER IN PLANT NUTRITION
Cieschi MT1, Naranjo MA2, Menéndez N3 and Lucena JJ1
1Department of Agricultural Chemistry and Food Science, Autonomous University of Madrid, 28049 Madrid.
SPAIN ([email protected])
2 Departamento I+D FERTINAGRO NUTRIENTES SL
3Department of Applied Physical Chemistry, Autonomous University of Madrid, 28049 Madrid. SPAIN
Iron fertilizers based on humic substances extracted from lignites, such as leonardite, are used in the
Mediterranean area (as liquid concentrates) in drip irrigated fruit tree plantations 1. This kind of iron complexes
fertilizers are biodegradable and cheaper than synthetic iron chelates but less efficient correcting iron chlorosis.
Chen et al2 suggested that humic substances enhance iron uptake by plants because of their ability to form
metal complexes, although it depends on their stability and solubility, among another factors3. Many authors4,5
have observed improved yield, mineral uptake and fruit quality when leonardite was applied to field but there
is scarce agronomical studies about iron leonardite application to orange trees in calcareous soils, yet. The
aim of this work is to evaluate the kinetic effects of an iron leonardite fertilizer in plant nutrition taking into
account controlled and field conditions.
Iron humate was characterized by Mössbauer spectroscopy and X ray diffraction. The iron chelate
reductase activity was assessed in cucumber deficient plants. A hydroponic assay was conducted with different
dosses of iron humates (10, 20, 50 and 100 µM) for twenty-one days using soybean iron deficient plants under
controlled conditions. In order to evaluate the iron complex kinetic behavior, a ligand competition assay
between iron leonardite fertilizer, BPDS and EDDHA or HBED at pH 7 was done for months. A chlorotic orange
(Citrus clementina Hort. ex Tanaka, ClemenRubí PRI 23) farm situated in Valencia (Spain) was fertilized with
iron leonardite fertilizer and FeEDDHA for a year, comparing iron content in leaves along the entire process
and yield and fruit quality at the end of the experiment.
Mössbauer spectra showed iron (III), compatible with polynuclear structures, is prevalent in the product.
The iron chelate reductase activity was null for cucumber deficient plants. At the end of the hydroponic
experiment, plants fertilized with 100 µmol presented adequate iron nutrition, having large amount of Fe
precipitated on the roots. The ligand competition showed a very slow release of iron bind to humate and a
progressive formation of iron (III) chelate (EDDHA or HBED) and iron (II), (BPDS) 3. Orange trees treated with
iron leonardite fertilizer presented similar yield and fruit quality and iron nutrition than FeEDDHA treated trees
at the end of the field assay.
Iron leonardite fertilizers are apparently less efficient than iron chelates in soil because of kinetics effects
but, at high doses, they are capable to correct iron chlorosis in the long-term field experiment. They provide
increasing iron availability in the roots soil interface that allows a slow uptake of Fe by the plants. Although
further research is required, our study proposes that iron leonardite fertilizers probably form iron plaque on the
roots surface that induce a slow redox cycled process in the rhizosphere and, in this way, enable iron plant
nutrition.
Keywords: Kinetic, iron complex fertilizers, Mössbauer, leonardite.
REFERENCES
1-Kovács K, Czech V,Fodor F, Solti A, Lucena JJ, Santos-Rosell S, Hernández-Apaolaza, L. 2013. J.
Agric. Food Chem., 61:50.
2-Chen Y, Clapp C, Magen H. 2004. Soil Sci and Plant Nutr., 50:7.
3-Garcia-Mina JM. 2006. Org. Geochem., 258:1987.
4-Olego MA, Cordero J, Quiroga MJ, Sánchez-García M, Álvarez JC, Garzón-Gimeno E. 2015. ITEA,
111:3.
5-Eshghi S.and Garazhian M. 2015. Iran Agric. Res., 34:1.
ACKNOWLEDGEMENT: The project AGL2013-44474-R of Spanish Ministry of Science and Innovation and
Fertinagro SL financially supported this study.
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