Stability in solution and reactivity with soils and soil components of iron and zinc complexes

Abstract

Naturally derived complexes with the ability to complex (unidentate) or chelate (polydentate) metals are a cheaper alternative to synthetic chelates to correct micronutrient deficiencies, but despite their widespread use there is a lack of knowledge on their agronomic performance. The aim of this paper was to evaluate the stability of iron (Fe) and zinc (Zn) lignosulfonate, gluconate, amino acid, and humate complexes in solution over time and at different pH values. Also, their stability in a concentrated nutrient solution and their reactivity with soils and soil components was evaluated. In our experimental conditions, all the complexes (except Fe amino acid) remained stable in solution for an extended period of time. All Zn complexes and the Fe lignosulfonate were stable in solution up to pH 7.0–7.5, while Fe gluconate only maintained 20%–40% of the iron in solution in the pH range 5–11 and Fe amino acid and humate complexes barely maintained small concentrations of Fe in solution above pH 3. Most of the complexes maintained Fe and Zn in concentrated nutrient solutions for irrigation systems, but Fe amino acid only maintained around 70% of the iron added. In general, the interactions of complexes with soils and soil components produced a high retention. The interaction of Fe lignosulfonate with peat, illite, and ferrihydrite, and Fe gluconate with peat and illite resulted in significant amounts of Fe to remain in solution, while for the Fe amino acid and humate the Fe remaining in solution was low. All Zn complexes were highly retained in an acidic peat, illite, and montmorillonite clays and soils, while no retention was observed on ferrihydrite. In conclusion, the stability of complexes in different conditions is related to the percentage of complexed element in the products. While complexes can be used to maintain micronutrients in solution in aqueous media (foliar and fertigation), their application to soil should be considered as a measure to increase metal availabilities but not their solubility.

Effect of Fe:ligand ratios on hydroponic conditions and calcareous soil in Solanum lycopersicum L. and Glycine max L. fertilized with heptagluconate and gluconate

“…These complexing agents present a wide variety of functional groups, such as carboxylic and hydroxyl groups, which are also present in G7 and G6. The presence of other complexing agents in the complexing agents G6 and G7 used was discarded by theC NMR and FTIR spectra (Fig. ), thus confirming that the fact that there was a higher Fe 3+ complexing capacity for G7 than for G6 was not due to impurities.…”

“…in hydroponics, where the G6 was able to provide Fe to deficient soybean plants in a similar concentration to Fe 3+: EDTA and Fe 3+ :IDHA, but lower than for Fe 3+ :EDDHA. Lucena et al . also confirmed that the percentage of Fe remaining in solution for G6 in the pH range 5–7.5 was around 20%.…”

Inheritance of iron deficiency chlorosis resistance in groundnut (Arachis hypogaeaL.)

“…Application of inorganic-Fe fertilizer to soil is of little benefit as the Fe ionizes and gets converted into insoluble Fe 3C compounds, while foliar application has the problem of poor translocation of applied Fe within the plant (H€ uve et al 2003). Organic-Fe fertilizer is readily adsorbed onto soil particles, which can reduce the fertilizer effect, hence often used in soilless cultivation and as a foliar spray (Cesco et al 2000;Lucena, Garate, and Villen 2010). Chelated-Fe fertilizer is more expensive and often applied to high-value crops, hence economically not feasible in the semi-arid tropics where groundnut is mainly grown as a rainfed subsistence crop.…”

Residual effects of organic Zn fertilizers applied before the previous crop on Zn availability and Zn uptake by flax (Linum usitatissium)

“…The plant availability of this residual Zn depends, amongst other factors, on the source of Zn used. Organic Zn sources such as synthetic chelates and organic complexes are nowadays commonly used (Aboulroos, 1981;Al-Mustafa et al, 1994;Lucena et al, 2010). Gangloff et al (2002) have reported that Zn chelates are highly effective sources of Zn for crops.…”