Rates of foliar penetration of chelated Fe(III): role of light, stomata, species, and leaf age

Rates of foliar penetration of Fe(III) chelates of imidodisuccinic acid (IDHA), ligninsulfonic acid (Natrel), and citric acid (ammonium ferric citrate) were studied at 20 degrees C using a leaf disk method. After drying of the donor droplets, the humidity over the donor residues was maintained at 100% because Fe(III) chelates deliquesce only when humidity is higher than 90%. The wetting agent Glucopon 215 CSUP was added at a concentration of 0.2 g L(-1) to all donor solutions. With fully expanded stomatous broad bean leaves, penetration of Fe-IDHA followed first-order kinetics and rate constants of penetration were higher in light (0.073 h(-1)) than in the dark (0.042 h(-1)). Permeability of broad been leaves to CaCl2 was about 8 times higher than to Fe-IDHA. Doubling the Fe-IDHA concentration in the donor from 2.5 to 5 mmol L(-1) decreased rate constants of Fe-IDHA penetration by a factor of 2.2. Adding the silicon surfactant Break Thru S240 at 10 g L(-1) to the donor induced infiltration of open stomata and about 80% of the applied Fe-IDHA penetrated during droplet drying, while with Glucopon 215 CSUP stomatal infiltration was not observed. With broad bean leaves, penetration of Natrel and ammonium ferric citrate also followed first-order kinetics and rate constants were also higher in light than in the dark. Adaxial astomatous surfaces of fully expanded pear, apple, and grapevine leaves were practically impermeable to Fe-IDHA while stomatous abaxial leaf surfaces were permeable, but rate constants of penetration decreased with time and differed greatly among species. Astomatous surfaces of young unfurling grapevine and peach leaves were permeable to Fe-IDHA, but permeability of stomatous surfaces was much higher. The effect of light on permeability of stomatous leaf surfaces is attributed to the presence of aqueous pores in cuticles over guard cells, and it is suggested that permeability of these pores increases as stomata open. Consequences of these results for foliar applications of Fe chelates are discussed.     

Comparison of iron chelates and complexes supplied as foliar sprays and in nutrient solution to correct iron chlorosis of soybean

The application of synthetic chelates is the most efficient remedy for correcting iron (Fe) chlorosis. However, chelates are usually expensive and nondegradable products. Recently, new degradable chelates have been proposed for their use as Fe fertilizers. Also, Fe complexes cheaper than synthetic chelates and derived from natural products are also used to correct Fe deficiencies. Fifteen products, including five different synthetic chelates (Fe‐EDDS, Fe‐IDHA, and three Fe‐EDTA formulations) and ten natural complexes (humates, lignosulfonates, amino acids, glycoproteins, polyamines, citrate, and gluconate), have been compared when applied at low concentration to soybean (Glycine max L.) chlorotic plants grown in hydroponics under controlled conditions. In the first experiment, Fe compounds were applied to the nutrient solution, while in the second trial, Fe was foliar‐supplied. Dry matter, Fe concentration in shoots and roots, and SPAD values were used to evaluate the effectiveness of the Fe in the different products. In the nutrient‐solution experiment, synthetic chelates provided better plant growth, Fe concentration, and SPAD values than complexes. Among the Fe complexes, transferrin generally provided good plant responses, similar to those obtained with synthetic chelates. After foliar application, the highest regreening was observed for plants treated with synthetic chelates and amino acid complexes, but the translocation to roots only occurred for Fe lignosulfonate. Fe‐EDDS and Fe‐EDTA performed in a similar way when applied in nutrient solution or as foliar sprays.     

Potential use of biodegradable chelate N-(1,2-dicarboxyethyl)-D,L-aspartic acid/Fe3+ as an Fe fertilizer

In the past several years, concern about the environmental fate of recalcitrant synthetic ligands (e.g., EDTA) has increased. The used of new biodegradable chelating agents such as imidodisuccinic acid (IDHA) has been proposed as an alternative. However, its application as an iron ligand to correct iron chlorosis in agriculture has not yet been studied. Then the objective of this work is to determine the fertilizer capacity of IDHA/Fe3+ using interaction assays with soils and soil materials and evaluating Fe nutrition of efficient and susceptible plants. Interaction of IDHA/Fe3+ with soil materials produces a reduction of the amount of soluble Fe. This is in good agreement with studies on the stability of the IDHA/Fe3+ chelate. In general, plant response to IDHA/Fe3+ in hydroponics is acceptable and better than that to EDTA/Fe3+. This good behavior seems to be related to the lower coordination of the iron in IDHA/Fe3+ with respect to EDTA/Fe3+.     

Cuticular penetration of calcium salts: effects of humidity,anions, and adjuvants

Physical laws of cuticular penetration of calcium salts have been studied using astomatous isolated pear (Pyrus communis L.) leaf cuticular membranes (CM). Penetration followed first order kinetics and was greatly affected by humidity, hygroscopicity, solubility of salts, and nature of adjuvants. Penetration required dissolution of the salts and this is determined by their point of deliquescence (POD). POD corresponds to the humidity over a saturated salt solution containing undissolved salt. When humidity was above POD the salt residue on the cuticle dissolved, while below a solid residue was formed and penetration ceased. CaCl₂ and Ca(NO₃)₂ have POD's of 32 and 55%, respectively, while POD's of organic calcium salts (acetate, lactate, propionate) were between 95 and 100%. Furthermore, aqueous solubility of the inorganic calcium salts is one to two orders of magnitude higher than that of the organic salts. Thus, organic calcium salts are not well suited for foliar nutrition since POD's are very high and driving forces of penetration are low due to low solubility even at 100% humidity. CaCl₂ and Ca(NO₃)₂ penetrate even at low humidity and solubility is much higher. When humidity was above the POD, rate constants of penetration increased with increasing humidity by about a factor of three and maximum rates were measured at 100%. Temperature did not affect rate constants of penetration from which it can be concluded that penetration is most rapid during the night when humidity is high. All salts should be used with an effective wetter as with an alkyl polyglucoside half time of penetration was decreased from 204 to 17 h. All other adjuvants tested (protein hydrolysates, EDTA, gum guar) decreased rate constants of penetration by factors of 3 to 9. This finding is discussed in relation to mixing foliar nutrients with fungizides.     

Demetalation of Fe, Mn, and Cu chelates and complexes: application to the NMR analysis of micronutrient fertilizers

The application of nuclear magnetic resonance (NMR) for the quality control of fertilizers based on Fe(3+), Mn(2+), and Cu(2+) chelates and complexes is precluded by the strong paramagnetism of metals. Recently, a method based on the use of ferrocyanide has been described to remove iron from commercial iron chelates based on the o,o-EDDHA [ethylenediamine-N,N'bis(2-hydroxyphenylacetic)acid] chelating agent for their analysis and quantification by NMR. The present work extended that procedure to other paramagnetic ions, manganese and copper, and other chelating, EDTA (ethylenediaminetetraacetic acid), IDHA [N-(1,2-dicarboxyethyl)-d,l-aspartic acid], and complexing agents, gluconate and heptagluconate. Results showed that the removal of the paramagnetic ions was complete, allowing us to obtain (1)H NMR spectra characterized by narrow peaks. The quantification of the ligands by NMR and high-performance liquid chromatography showed that their complete recovery was granted. The NMR analysis enabled detection and quantification of unknown impurities without the need of pure compounds as internal standards.     

Interactions of calcium ions with weakly acidic active ingredients slow cuticular penetration: a case study with glyphosate

Potassium and calcium salts of glyphosate were obtained by titrating glyphosate acid with the respective bases to pH 4.0, and rates of penetration of these salts across isolated astomatous cuticular membranes (CMs) were measured at 20 degrees C and 70, 80, 90, and 100% humidity. K-glyphosate exhibited first-order penetration kinetics, and rate constants (k) increased with increasing humidity. Ca-glyphosate penetrated only when the humidity above the salt residue was 100%. At 90% humidity and below, Ca-glyphosate formed a solid residue on the CMs and penetration was not measurable. With Ca-glyphosate, the k value at 100% humidity decreased with time and the initial rates were lower than for K-glyphosate by a factor of 3.68. After equimolar concentrations of ammonium oxalate were added to Ca-glyphosate, high penetration rates close to those measured with K-glyphosate were measured at all humidities. Adding ammonium sulfate or potassium carbonate also increased rates between 70 and 100% humidity, but they were not as high as with ammonium oxalate. The data indicate that at pH 4.0 one Ca2+ ion is bound to two glyphosate anions. This salt has its deliquescence point near 100% humidity. Therefore, it is a solid at lower humidity and does not penetrate. Its molecular weight is 1.82 times larger than that of K-glyphosate, and this greatly slows down rates of penetration, even at 100% humidity. The additives tested have low solubility products and form insoluble precipitates with Ca2+ ions, but only ammonium oxalate binds Ca2+ quantitatively. The resulting ammonium salt of glyphosate penetrates at 70-100% humidity and at rates comparable to K-glyphosate. The results contribute to a better understanding of the hard water antagonism observed with glyphosate. It is argued that other pesticides and hormones with carboxyl functions are likely to respond to Ca2+ ions in a similar fashion. In all of these cases, ammonium oxalate is expected to overcome hard water antagonism.     

Theoretical speciation of ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA) in agronomic conditions

The presence of ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA) as the second largest component in commercial EDDHA iron chelates has recently been demonstrated. Here is reported the speciation of o,p-EDDHA by the application of a novel methodology through the determination of the complexing capacity, protonation, and Ca(2+), Mg(2+), Cu(2+), and Fe(3+) stability constants. The pM values and species distribution in solution, hydroponic, and soil conditions were obtained. Due to the para position of one phenol group in o,p-EDDHA, the protonation constants and Ca and Mg stability constants have different values from those of o,o-EDDHA and p,p-EDDHA regioisomers. o,p-EDDHA/Fe(3+) stability constants are higher than those of EDTA/Fe(3+) but lower than those of o,o-EDDHA/Fe(3+). The sequence obtained for pFe is o,o-EDDHA/Fe(3+) >/= o,p-EDDHA/Fe(3+) > EDTA/Fe(3+). o,p-EDDHA/Fe(3+) can be used as an iron chelate in hydroponic conditions. Also, it can be used in soils with limited Cu availability.     

Chemical properties and reactivity of manganese chelates and complexes in solution and soils

Commercial fertilizers containing synthetic manganese (Mn) chelates and complexes are currently used to alleviate Mn deficiency in crops. However, studies conducted on Mn sources in order to evaluate their behavior maintaining Mn soluble in nutrient solution and soil have not been done. In this work, representative commercial Mn fertilizers based on chelates and complexes were characterized and their chemical stability in solution and interaction with soils has been evaluated. Fertilizers studied were two ethylene diamine tetraacetic acid (EDTA) Mn chelates, one N‐(1,2‐dicarboxyethyl)‐D,L‐aspartic acid (IDHA) Mn chelate, two lignosulfonates, one carboxylate, one fulvate, one gluconate, and one heptagluconate‐based Mn complex. Characterization consisted of the determination of the soluble and chelated or complexed Mn, and the ligand identification by nuclear‐magnetic resonance (NMR). Stability study included batch experiments in Ca solution at different pH and three batch experiments with soil comparing with MnSO₄. Results indicate that most of the Mn fertilizers comply with the declared “soluble and chelated or complexed” metal content. At a usual pH range of calcareous soils (7.5–8.5), both chelates and complexes maintain more Mn in solution than MnSO₄ in the presence of Ca. Several factors affect the Mn remaining in solution after the interaction with the soil, especially, the soil‐to‐solution ratio. All chelates and complexes are better alternatives to the use of MnSO₄ in agronomical practices such as fertigation and soil application. Mn‐IDHA as chelate and Mn‐HGl or Mn‐Carb as complexes can be efficient, economical, and environmental friendly fertilizers for foliar application and hydroponic cultures. In soil application, Mn‐EDTA or Mn‐LS would be the best options. In this case, lignosulfonic acid represents a sustainable and low‐cost solution.     

Distribution pattern of root‐supplied 59iron in iron‐sufficient and iron‐deficient bean plants

In order to study the iron (Fe) distribution pattern in bean plants with different Fe nutritional status, french bean (Phaseolus vulgaris L.) seedlings were precultured in a complete nutrient solution with 8x10^‐5 M FeEDTA for five days. Thereafter, plants were further supplied with 8x10^‐5 M FeEDTA (Fe‐sufficient) or with only 2x10^‐6 M FeEDTA (Fe‐deficient) for another eight days. At this stage, the Fe‐deficient plants had much lower chlorophyll contents and lower dry weight of the leaves but higher reducing capacity of the roots compared with the Fe‐sufficient plants. For studies on short‐term distribution of Fe, the Fe‐sufficient plants were supplied 8x10^‐5 M ⁵⁹FeEDTA (specific activity 9.9 GBq/mol) and the Fe‐deficient plants 1x10⁶ M ⁵⁹FeEDTA (specific activity 98.8 GBq/mol). The plants were harvested after 4 and 24 hours. Despite a much lower supply of ⁵⁹FeEDTA/(factor 80), the Fe‐deficient plants took up significantly more ⁵⁹Fe but translocated less to the shoots (14.6% after 24 h) compared with the Fe‐sufficient plants (29.4% after 24 h). However, regardless of the Fe nutritional status of the plants, the majority of ⁵⁹Fe was translocated in the primary leaves. Our results demonstrate a similar distribution patterns of root‐derived ⁵⁹Fe in the shoots of Fe‐sufficient and Fe‐deficient plants, and thus, no preferential direct translocation of Fe to the shoot apex in the Fe‐deficient plants.     

Iron dissociates from the NaFeEDTA complex prior to or during intestinal absorption in rats

Sodium iron ethylenediaminetetraacetate (NaFeEDTA) has superior iron bioavailability especially in foods containing iron absorption inhibitors. However, mechanisms involved in the absorption and subsequent partitioning of iron complexed with EDTA are poorly understood. Our objectives were to compare retention and tissue distribution of iron administered to rats either as FeSO4 or NaFeEDTA, either orally (OR) or subcutaneously (SC). Weanling rats were fed semipurified diets supplemented with either FeSO4 or NaFeEDTA for 7 days. They were then given a meal containing 59Fe-labeled FeSO4 or NaFeEDTA, or they were injected SC with these two forms of radiolabeled Fe. 59Fe retention was measured by whole body counting. Urine was collected and counted at 24 h intervals throughout the counting period. Tissue samples were analyzed for nonheme iron and 59Fe activity. Absorption of iron from FeSO4 or NaFeEDTA was similar (57.7 and 53.4%, respectively). Seventy-seven percent of the injected Na59FeEDTA was excreted in the urine within 24 h, whereas only 0.5, 0.8, and 1.4% of the injected 59FeSO4, oral 59FeSO4, and oral Na59FeEDTA, respectively, was excreted in the urine. The nonheme iron content was lower in the liver and spleen, by 56.8 and 28.4%, respectively, among rats consuming the NaFeEDTA diet as compared to rats fed FeSO4. We conclude that iron is dissociated from EDTA prior to or during intestinal absorption and that some fraction of the dissociated EDTA is absorbed separately from the iron.     

The role of EDTA in malonaldehyde formation from DNA oxidized by Fenton reagent systems

Calf thymus DNA was oxidized by various Fenton reagent systems [Fe(II)/H(2)O(2)] with or without ethylenediamine tetraacetic acid (EDTA) under different reaction conditions. Calf DNA was also oxidized by a modified Fenton reagent (Fe(III)/H(2)O(2)/ascorbic acid) with EDTA. Malonaldehyde (MA) formed from DNA was derivatized into 1-methyl hydrazine, which was subsequently analyzed by gas chromatography with a nitrogen-phosphorus detector. MA formation increased linearly with an increase of Fe(II) concentration. MA formation reached a plateau at nearly 2 mmol/L of Fe(II) with 0.5 mmol/L of H(2)O(2). Addition of EDTA increased MA formation from DNA nearly 5 times. When DNA was oxidized with various amount of ethanol, MA formation decreased with an increase of ethanol concentration, either with or without EDTA. The rate of inhibition was greater without EDTA than with EDTA. When DNA was oxidized by a modified Fenton reagent, MA formation linearly increased with the increase of DNA. Ascorbic acid alone produced some MA upon oxidation.     

Interaction of Different Iron Chelates with an Alkaline and Calcareous Soil: A Complementary Methodology to Evaluate the Performance of Iron Compounds in the Correction of Iron Chlorosis

Abstract

A great number of studies have shown that the stability of iron chelates as a function of pH is not the unique parameter that must be considered in order to evaluate the potential effectiveness of Fe‐chelates to correct iron chlorosis in plants cultivated in alkaline and calcareous soils. In fact, other factors, such as soil sorption on soil components or the competition among Fe and other metallic cations for the chelating agent in soil solution, have a considerable influence on the capacity of iron chelates to maintain iron in soil solution available to plants. In this context, the aim of this work is to study the variation in concentration of the main iron chelates employed by farmers under field conditions—Fe‐EDDHA (HA), Fe‐EDDHMA (MA), Fe‐EDDHSA (SA), Fe‐EDDCHA (CA), Fe‐EDTA (EDTA), and Fe‐DTPA (DTPA)—in the soil solution of a calcareous soil over time. To this end, soil incubations were carried out using a soil:Fe solution ratio corresponding to soil field capacity, at a temperature of 23°C. The soil used in the experiments was a calcareous soil with a very low organic matter content. The variation in concentration of Fe and Fe‐chelates in soil solution over time were obtained by measuring the evolution in soil solution of both the concentration of total Fe (measured by AAS), and the concentration of the ortho‐ortho isomers for Fe‐EDDHA and analogs or chelated Fe for Fe‐EDTA and Fe‐DTPA (measured by HPLC). The following chelate samples were used: a HA standard prepared in the laboratory and samples of HA, MA, SA, CA, Fe‐EDTA, and Fe‐DTPA obtained from commercial formulations present in the market. The percentage of iron chelated as ortho‐ortho isomers for HAs was: HA standard (100%); HA (51.78%); MA (60.06%); SA (22.50%); and CA (27.28%). In the case of Fe‐EDTA and Fe‐DTPA the percentages of chelated iron were 96.09 and 99.12, respectively. Results show that it is possible to classify the potential effectiveness of the different types of iron chelates used in our experiments as a function of two practical approaches: (i) considering the variation of total iron in soil solution over time, MA is the best performing product, followed by HA, CA, SA, DTPA, EDTA, and ferrous sulfate in the order listed and (ii) considering the capacity of the different iron chelates to maintain the fraction of chelated iron (ortho‐ortho isomers for HA, MA, SA, and CA and total chelated iron for EDTA and DTPA) in soil solution, the order is: SA > CA > HA > MA > EDTA ≈ DTPA. This result, that is related to the nature of the chelate and does not depend on the degree of chelated Fe in the products, indicates that SA and CA might be very efficient products to correct iron chlorosis. Finally, our results also indicate the suitability of this soil incubation methodology to evaluate the potential efficiency of iron compounds to correct iron chlorosis.     

Determination of suitable chemical extraction methods for the available iron content of brown forest soils in Turkey

The aim of this research was to determine the available iron (Fe) content of brown forest soils of Edirne Province and the most suitable chemical extraction method. Eight chemical extraction methods (the 0.005 M DTPA + 0.01 M CaCl2 + 0.1 MTEA, 0.05 M HCl + 0.012 M H2SO4, 1 M NH4OAc (pH: 4.8), 0.01 M EDTA + 1 M NH4OAc, 1 M MgCl2, 0.01 M EDTA + 1 M (NH4)2CO3, 0.005 M DTPA + 1 M NH4HCO3, and 0.001 M EDDHA methods) and six biological indices (the dry matter yield, Fe concentration, Fe uptake, relative dry matter yield, relative Fe concentration, and relative Fe uptake) were compared. The biological indices were determined with barley (Hordeum vulgare L.) grown under greenhouse conditions. At the end of the experiment, the highest correlation coefficients (r) were determined to be between the 0.005 M DTPA + 0.01 M CaCl2 + 0.1 M TEA method and the biological indices and between the 0.005 M DTPA + 1 M NH4HCO3 method and the biological indices. The corresponding correlation coefficients (r) for the 0.005 M DTPA + 0.01 M CaCl2 + 0.1 M TEA method and the six biological indices were 0.621**, 0.823**, 0.810** 0.433**, 0.558**, and 0.640**, respectively. For the 0.005 M DTPA + 1 M NH4HCO3 method, these coefficients were equal to 0.618**, 0.520**, 0.679**, 0.521**, 0.492**, and 0.641**, respectively (** indicate the validity of the relationships at p < 0.01) These extraction methods, out of all the methods tested, were suggested for the determination of the available Fe content of the brown forest soils. Published in Russian in Pochvovedenie, 2006, No. 9, pp. 1068–1074. The text was submitted by the author in English.     

Plant-Available Phosphorus after Application of Synthetic Chelating Agents

Fertilizer phosphorus (P) can become immobilized in acidic soils through bonds with iron (Fe) and aluminum (Al). Two chelating agents, ethylenediamine tetraacetic acid disodium salt (EDTA) and hydroxyethyl ethylenediamine triacetic acid (HEEDTA), were tested in a greenhouse study for efficiency at increasing plant-available P to corn (Zea mays L.). Fertilizer P was added with or without chelate to the center of pots, simulating a starter band of P. Without the presence of chelates, biomass above and below ground increased linearly as P fertilizer rates increased at 0, 9.6, 19.3, 28.9, and 38.5 kg P ha^?1. Applications of EDTA and HEEDTA did not significantly increase water-soluble P (WSP), Mehlich 1 P, and Mehlich 3 P compared to soils without chelates. Applications of EDTA increased P uptake in the belowground biomass. Despite previous research showing that chelates increased WSP in soils, a decrease in P sorption was not observed with the additions of chelating agents to soils.     

The use of iron chelates in compound fertilizers containing trace elements

Abstract

The chemical behaviour of iron chelates, incorporated in compound fertilizers with inorganic micronutrient compounds, was studied. Pot experiments were conducted to evaluate the effectiveness of these products in controlling iron deficiency. A commercial compound fertilizer, containing 0.09% Fe as Fe‐DTPA, 0.12% Cu, 0.16% Mn and 0.04% Zn as sulfates, proved to be ineffective in preventing iron chlorosis in Chamaecyparis lawsoniana ’Alumii’, growing on sphagnum peat at two lime levels. The same fertilizer formulation with 0.09%‐ Fe as Fe‐EDDHA did prevent iron chlorosis at both lime levels. Fe‐EDTA, incorporated in the compound fertilizer, gave good results at the lower but not at the higher lime level, due to the low stability of Fe‐EDTA at high pH. Data from laboratory experiments showed that copper replaced the chelated iron in the compound fertilizer containing Fe‐DTPA, causing the iron to precipitate. The strong competition between copper and iron for the organic ligand is due to a specific affinity of copper for DTPA, resulting in a copper chelate with high stability constant and a molar ratio of copper to chelating agent of 2 : 1.

In the case of Fe‐EDDHA and Fe‐EDTA the competition between iron and copper is much weaker. In contrast to Fe‐DTPA, these chelates remain rather stable when incorporated in fertilizers containing micronutrients.     

EDTA辅助小藜修复Pb及Pb-Cd复合污染土壤的研究

通过盆栽试验,研究了Pb及Pb-Cd复合污染土壤添加EDTA（乙二胺四乙酸）对小藜生长和转运、富集Pb、Cd的影响。结果表明,高浓度的EDTA对小藜的生长有抑制作用,Pb及Pb-Cd复合处理下EDTA最佳添加浓度均为2.5 mmol·kg^-1,此时小藜对Pb的转运系数达2.66和2.41,富集系数达1.51和1.82,分别比对照提高554%和493%、8 431%和2 367%;对Cd的转运系数达1.87和3.47,富集系数达1.78和10.8,分别比对照提高165%和355%、77%和283%。2.5 mmol·kg^-1EDTA辅助小藜修复Pb-Cd复合污染土壤的效果优于修复Pb污染土壤的效果。     

Interaction of iron chelates with several soil materials and with a soil standard

Frequently the effectiveness of iron (Fe) chelates is low because they can be retained or destroyed by soil materials. The high cost of these Fe fertilizers makes it necessary to study soil material reaction with Fe chelates. Commercial Fe chelates with EDTA, EDDHA, and EDDHMA as ligands and their standards, prepared in the laboratory, were shaken for one hour with various soil materials [amorphous Fe(III) oxide, acid peat, calcium (Ca)‐montmorillonite and calcium carbonate (CaCO₃)] and with a soil standard made in the laboratory. After agitation, the chelate‐soil mixtures were filtered and the micronutrients and chelated Fe that remained in solution were determined. Among the soil materials used, amorphous Fe(III) oxide and acid peat had the greatest affect on the amount of chelated Fe remaining in solution. The type of chelating agent was the next major factor that affected the availability of soluble Fe following reaction with the soil materials. Another factor was the commercial formulation of the Fe chelates. The chelates comprised of EDDHA or EDDHMA maintained the highest percentages of chelated Fe in solution after interaction with the solid phases, except for the acid peat. The last soil material, acid peat, retained more chelated Fe for the Fe chelates with EDDHA or EDDHMA than with EDTA as the chelating agent. The commercial Fe‐EDDHA chelates had greater losses of chelated Fe than their standard after interaction with all the solid phases. The commercial Fe‐EDDHA chelate (Sequestrene) and the commercial Fe‐EDDHMA chelate (Hampirón) solubilized the highest amount of copper (Cu) from soil standard. This was attributed to the presence of by‐products in the commercial formulations since the Fe‐EDDHA standard did not have Cu in solution after the interaction. Therefore, the commercial Fe chelate by‐products are able to form Cu‐complexes which could affect chelated Fe and its availability to plants.     

Effectiveness of iron chelates and FeSO4 for correcting iron chlorosis of peanut on calcareous soils

The effectivenness of different Fe chelates to correct lime induced chlorosis of peanut (Arachis hypogaea) was tested on calcareous soils in Cyprus. Among the chelates tested, Fe‐DTPA and Fe‐EDTA were less effective than Fe‐EDDHA. In one experiment. Fe‐EDDHMA Was less effective while in another experiment was equally effective compared to Fe‐EDDHA . Three different commercial chelates of the form Fe‐EDDHA were equally effective in correcting iron chlorosis. The stability of the Fe‐EDDHA chelate in the soil does not affect its efficiency in curing chlorosis of peanut due to the short growing season for this crop. Ferrous sulfate applied without an acidifying soil amendment was not effective to correct iron chlorosis of peanut.     

Inulin affects iron dialyzability from FeSO4 and FeEDTA solutions but does not alter Fe uptake by Caco-2 cells

The in vitro effects of inulin on the fluxes of Fe (F(Fe)) and uptake by Caco-2 cells from FeSO4 and FeEDTA were evaluated. Cell ferritin formation was used as a measure of Fe uptake. Mitochondrial (MTT test) and lysosomal activities were monitored as biomarkers of the changes of cellular metabolism. Changes in mRNA expression of Fe transporters, DMT1 and Dcytb, were evaluated. Inulin decreased dialyzability and F(Fe) from FeSO4 solution, suggesting a mineral binding effect, but increased those from FeEDTA. Cultures exposed to FeEDTA solutions exhibited higher ferritin values and MTT conversion percentages. Regardless of Fe source, cell Fe uptake and mRNA expression of Fe transporters were similar with or without inulin, suggesting that inulin did not impair Fe uptake. These observations might indicate a faster cellular Fe internalization from FeEDTA solutions. From a physiological perspective, the decreased F(Fe) from FeSO4 might be reflected in a decreased Fe uptake.     

Impact of liming on utilization of 59Fe‐chelates by lettuce (Lactuca sativa L.)

A pot experiment was conducted to determine the utilization of iron (Fe) by lettuce (Lactuca sativa L. cv. Australian gelber). Iron was applied as ⁵⁹Fe in inorganic and chelated form, particularly biodegradable chelate, ⁵⁹Fe‐EDDS. Two stereoisomeric forms of ethylenediaminedisuccinate: [S,S]‐EDDS and a mixture of EDDS containing 25% [S,S]‐EDDS, 25% [R,R]‐EDDS, and 50% [S/R]/[R/S]‐EDDS, ethylenediaminetetraaceticacid (EDTA) and ethylenediimino bis(2‐hydroxyphenyl)acetic acid (EDDHA) were used as ligands. Lettuce was grown in unlimed and limed quartz sand with nitrate as the sole source of nitrogen. Liming decreased lettuce yields but had no effect on Fe concentrations, indicating that Fe concentrations were a poor indicator of Fe bioavailability within the plant. In unlimed sand, utilization of ⁵⁹Fe from all ⁵⁹Fe‐chelates was on the same level (2.8%–3.6%). In limed sand, only ⁵⁹Fe‐EDDHA maintained the ⁵⁹Fe utilization on a level (3%) comparable to that in unlimed sand. Although the utilization of ⁵⁹Fe from the other chelates decreased to 0.6%–1.1% after liming, Fe concentrations were not affected due to the increased uptake of indigenous Fe. The most biodegradable form of EDDS, namely ⁵⁹Fe‐EDDS(S,S), provided ⁵⁹Fe for lettuce as efficiently as the mixture of ⁵⁹Fe‐EDDS stereoisomers and the ⁵⁹Fe‐EDTA. Utilization of ⁵⁹Fe in inorganic form was 0.5% and 0.03% in unlimed and limed sand, respectively. This study shows that biodegradable ligands are able to serve as chelators to sustain Fe availability in calcareous environments. They may be of use especially in drip irrigation, where ligand accumulations may pose a threat to groundwater quality.