Characterization of commercial iron chelates and their behavior in an alkaline and calcareous soil

Iron deficiency is a common problem for many plants grown in alkaline and calcareous soils. To correct this problem, iron is supplied to plants as chelates. Several iron chelates are sold under diverse trademarks with different characteristics. This work evaluated 18 commercial products containing the most representative chelated iron sources used in agricultural practice in Spain when the study was done, namely the ferric chelates of EDDHA, EDDHMA, EDDCHA, EDDHSA, EDTA, and DTPA. The chelates were comprehensively characterized and quantitated by several techniques, including several chromatographic methods. Iron and chelate dynamics in soil were also studied in a model alkaline and calcareous soil. Results indicate that, in this model soil, among the different iron compounds studied only FeEDDHA and analogues have the capacity to maintain soluble iron in soil solution over time. These results are in agreement with general experience under field conditions. Furthermore, among the different ortho-ortho isomers of FeEDDHA's, FeEDDHSA and FeEDDCHA showed greater capacity than FeEDDHA and FeEDDHMA to maintain the chelated iron in soil solution over time.     

Effects of synthetic and microbially produced chelates on the diffusion of iron and phosphorus to a simulated root in soil

Summary Hydroxamate siderophores (HS) are microbially produced, ferric-specific chelates, known to occur in soil, and to be capable of providing iron to higher plants. This study examined the potential for HS to influence the diffusion of both iron and phosphorus to plant roots in soil.The HS desferrioxamine-B (DFOB) and desferriferrichrome (ferrichrome) were compared with the synthetic chelates ethylenediamine [di(o-hydroxyphenylacetic)acid] (EDDHA) and ethylenediamine-tetraacetic acid (EDTA), and citrate, oxalate, and distilled water in their ability to increase diffusion of iron using a simulated root technique. Chelate solutions were pumped through porous fiber bundles imbedded in soil previously labeled with⁵⁵Fe. In a sandy loam of pH 7.5,⁵⁵Fe diffusion caused by 10^–4 M DFOB was twice that of water, but similar to that caused by 10^–4 M EDDHA. However, 10^–3 M EDDHA resulted in greater diffusion than 10^-3 M DFOB. The diffusions resulting from equimolar quantities of citrate, oxalate, and EDTA were similar to that with distilled water. In a clay soil of pH 5.2 previously labeled with⁵⁵Fe and³² P, the response in⁵⁵Fe diffusion to chelate treatments was: 10^–4 M EDDHA > 10^–4 M ferrichrome > 10^–3 M DFOB > 10^–4 M DFOB > water. Both ferrichrome and EDDHA caused² P diffusion to increase substantially over that of distilled water. These results suggest that hydroxamate siderophores present in the rhizosphere could effectively increase the level of soluble iron for root uptake and possibly increase phosphorus uptake by solubilization of phosphorus from iron phosphates at acid pH.     

Analysis of iron chelates in commercial iron fertilizers by gel chromatography

A gel chromatographic method for the quality control of iron chelate fertilizers is described. The iron chelates are separated on a column of Sephadex G-10 and the eluates are analysed for iron. Using a sample quantity of 25 mg in a volume of 5 ml water and eluting with 0.15 M soidum chloride solution, a separation was achieved of commercial products of Fe-EDDHA or Fe-EDDHMA. The chromatographic analysis of Fe-EDTA or Fe-DTPA calls for a better resolution. This was obtained by decreasing the sample quantity and eluting with 0.035 M calcium chloride solution of pH 7.0. In this way it is possible to eliminate the interference of iron chelates of moderate stability which can be present in commercial products containing Fe-EDTA or Fe-DTPA.     

The stability of iron chelates in calcareous soils

The stability of Fe-EDTA and Fe-CDTA was investigated in order to evaluate their effectiveness under calcareous soil conditions. To accomplish this evaluation the reaction rate of fixation, K, the adsorption coefficient, K_d, and the retardation factor, S, of the iron chelate were determined through column experiments at pH 7.8 and two ionic strengths, I, of CaCl₂. The results indicated that iron in Fe-EDTA was more fixed than in Fe-CDTA. The fixation increased by increasing the ionic strength. Also it increased linearly with increasing CaCO₃ content of the soil. The values of retardation factor, S, showed that this parameter depended more on the surface area of the soil than on I or CaCO₃ content. The product KS depends on CaCO₃ content, surface area of the soil, ionic strength and chelating agent used. It can be taken as an index for the efficiency of the iron chelate under different conditions. Fe-EDTA was more adsorbed than Fe-CDTA, the adsorption increased with increasing ionic strength and surface area of the soil.     

Interaction of iron chelate and nitrogen fixation in peanuts grown on calcareous soil

The interaction of iron (Fe) nutrition and nitrogen (N₂) fixation was examined in peanuts grown in the field for two growing seasons. The treatments were: a) inoculated with Rhizobium, not fertilized with N, b) uninoculated, fertilized with N, and c) uninoculated not fertilized with N. These treatments were tested with or without Fe chelate application. Inoculated peanuts produced up to 42% higher N yield than the uninoculated, non‐fertilized plants. Moderately chlorotic peanuts fertilized with Fe did not increase significantly their yield but had bigger nodules than peanuts not fertilized with Fe. There were no interactions between Fe and N treatments, indicating that both nutrients were important for growth and for N₂ fixation. Remedy of Fe chlorosis on calcareous soils with FeEDDHA will not reduce N₂ fixation.     

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.     

Effect of carbon dioxide on the stability of iron chelates

The effect of carbon dioxide partial preassure on the stability of iron chelates in calcareous soils is often laid aside. Theoretical stability diagrams have been developed showing the large importance of this compound on total iron solubility from Fe‐EDTA and ‐DTPA chelates. As CO₂ increases free Ca²⁺ activity in solution decreases. Then chelation of iron increases. CO₂ partial preassure does not change the stability of Fe‐EDDHA since percentage of chelation is 100% in all conditions tested for this chelate.

Experimental data fit theoretical diagrams well when CO₂ partial preassure is high, but when CO₂ ^‐free air is used, chelation is greater than expected. Causes that can produce this difference are discussed.     

Effect of redox conditions on phosphate exchangeability and iron forms in a soil amended with ferrous iron

Application of iron (Fe) -rich amendments to soils has been proposed as a means of decreasing phosphorus (P) losses from soils. However, anoxic conditions following soil saturation are known to increase Fe and P solubility in soils, thus cancelling out the potential benefits. Our aim was to evaluate the effects of continuous oxic, continuous anoxic and alternating anoxic/oxic conditions on P exchangeability and Fe forms in soil amended with Ca(OH)₂ and FeSO₄. We incubated amended and unamended soils under these conditions for 8 weeks and measured Fe forms and P exchangeability. Under oxic conditions, addition of Ca(OH)₂ and FeSO₄ resulted in a strong decrease in P exchangeability and an increase in oxalate-extractable Fe. Mössbauer analyses suggested that an unidentified Fe oxide (D1oxide) with a strong sorbing capacity for P was precipitated. Under continuously anoxic conditions, P exchangeability and oxalate-extractable Fe increased with or without the amendments. Mössbauer analyses suggested that there was a partial dissolution of the D1oxide phase, precipitation of another unidentified Fe oxide (S3) and a reduction of structural Fe³⁺ in phyllosilicate, thereby increasing soil negative charge. These transformations resulted in a strong increase in rapidly exchangeable P. Alternating anoxic and oxic periods induced the dissolution and precipitation of iron oxides and the increase and decrease in P exchangeability. Implications of the results for limiting P losses from grassland soils are discussed.     

Inhibition of iron uptake from iron salts and chelates by divalent metal cations in intestinal epithelial cells

Iron chelates, namely, ferrous bisglycinate and ferric EDTA, are promising alternatives to iron salts for food fortification. The objectives of this study were to compare iron uptake from radiolabeled ferrous sulfate, ferrous ascorbate, ferrous bisglycinate, ferric chloride, ferric citrate, and ferric EDTA by Caco-2 cells with different iron status and in the presence of divalent metal cations. Iron-loaded Caco-2 cells, with reduced DMT-1 and elevated HFE mRNA levels, down-regulated uptake from ferrous ascorbate and bisglycinate but not from ferric compounds. Nevertheless, iron uptake from all compounds was markedly inhibited in the presence of 100-fold molar excess of Co2+ and Mn2+ cations, with ferrous compounds showing a greater percent reduction. Our results suggest that ferrous iron is the predominant form of iron taken up by intestinal epithelial cells and the DMT-1 pathway is the major pathway for uptake. Iron uptake from chelates appears to follow the same pathway as uptake from salts.     

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.     

Interaction of naphthalene and naphthol with soil organic matrix

The sorption of naphthalene and naphthol from water solutions by peat, chernozem, and humic and fulvic acids was studied. The sorption isotherms of naphthalene and naphthol by chernozem corresponded to the Langmuir isotherms. More complex nonlinear isotherms were obtained for peat. Binding of naphthalene and naphthol by humic and fulvic acids can proceed through hydrophobic interactions with aromatic fragments of humic substances and hydrogen bonds between the polar groups of humic molecules and naphthol OH groups.     

Effects of green iron nanoparticles on iron changes and phytoavailability in a calcareous soil

Green iron nanoparticles (Fe NPs) can be a practical solution to combat iron (Fe) deficiency in calcareous agricultural soils. The main aim of the present work was to assess the effects of green Fe NPs on Fe availability in calcareous soils. For this purpose, green Fe NPs were synthesized using green tea (G-Fe NPs), Shirazi thyme (T-Fe NPs), walnut green hull (W-Fe NPs), and pistachio green hull (P-Fe NPs) extracts and applied as a source of Fe fertilizer to sorghum (Sorghum bicolor L. Moench) plants. Results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and dynamic light scattering (DLS) indicated that the green Fe NPs were amorphous in nature and the polyphenols obtained from plant-part extracts acted as both capping and reducing agents. Similar to the behavior of Fe-ethylenediamine-N,N''-bis(2-hydroxyphenyl) acetic acid (Fe-EDDHA) in calcareous soils, G-Fe NPs, T-Fe NPs, W-Fe NPs, and P-Fe NPs increased Fe release compared with the control and FeSO₄ treatment. Cumulative Fe release data fitted well to the power function, intra-particle diffusion, and Elovich kinetic models. According to the pot experiment, the increment in soil Fe availability upon Fe-EDDHA and Fe NPs application led to an increase in Fe uptake, growth, and photosynthetic pigment contents of the sorghum plants. Although further research is needed to evaluate the residual effect and environmental impact of green Fe NPs, they may be an appropriate substitute for traditional Fe fertilizers in calcareous soils.     

Fractionation of copper and cadmium and their binding with soil organic matter in a contaminated soil amended with organic materials

Purpose  

The contamination of agricultural soils by heavy metals is a worldwide problem. Organic amendments can be used for the immobilization and binding of heavy metal ions in soils by complexation, adsorption, and precipitation. A field trial was carried out to evaluate the influence of some low-cost organic materials such as rice straw (RS), green manure (GM), and pig manure (PM) on the distribution of Cu and Cd and the retention of these metals by organic matter fractions in heavy metal-polluted soils.     

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.     

Interaction of aluminum and iron oxides and clay minerals and their effect on soil physical properties: A review

Abstract

Amorphous and crystalline aluminum and iron oxide minerals play a major role in stabilizing soil structure as measured by aggregate stability and clay dispersion. Aluminum and iron oxide interactions with clays are pH dependent. At low pH, where the oxides carry sufficient positive charge, they precipitate on clay surfaces. These coatings, once formed, are stable at higher pHs. Precipitation of oxides at high pH occurs as phases separate from the clays. Aluminum and iron oxides stabilize clay minerals by decreasing critical coagulation concentration, clay dispersion, water uptake, and clay swelling and by increasing microaggregation. The presence of aluminum and iron oxide minerals in soils has a favorable effect on soil physical properties, increasing aggregate stability, permeability, friability, porosity, and hydraulic conductivity, and reducing swelling, clay dispersion, bulk density, and modulus of rupture.     

Aluminium and iron oxides affect the soil structure in a long-term mineral fertilised soil

Journal of Soils and Sediments - The influence of iron and aluminium (hydr)oxide on soil aggregation is still not sufficiently understood. Therefore, we undertook a study on the effects of Al and...     

Precipitation of iron in a poorly drained alluvial soil

Abstract

Ferruginous deposits from the outfall and backfill of a newly‐installed drainage scheme in a poorly drained alluvial soil have been characterised using selective chemical dissolution, X‐ray diffraction, and chemical analysis and compared with the iron (Fe) deposits found in various micro‐environments within the soil profile. In the drainage ditch and on the permeable backfill around the drainage pipes, the mineralogy of the ferruginous deposits is dominated by the poorly ordered mineral, ferrihydrite, whereas within the soil environment the hydrous iron oxides display a wider range of structural order. It is probable that the initial precipitation product is poorly‐ordered material but that within the soil transformation to a more well ordered mineral, goethite, can occur.     

旱地土壤氮素矿化参数与氮素形态的关系

应用间歇淋洗培养方法 ,以长期不同培肥定位试验土壤为研究对象 ,求得土壤氮素矿化参数 ,并探讨氮素矿化潜势 (N0)、碱解氮、微生物氮、可浸提易矿化氮、全氮之间的关系。结果表明 ,在 35℃和 20℃条件下培养 ,一级动力学模型能够很好的拟合试验数据 ,模拟方程和模拟参数均达到极显著水平。经过 15年的培肥和轮作 ,无论是单施氮肥区 ,还是氮肥与有机肥配合施用区 ,N0均有不同程度的增加 ,这标志着土壤活性有机氮库增加。k值变化范围在0.004628～0.013148d-1之间 ,说明可矿化氮以每天 0.46 %～1.31%的平均速率矿化释放。而且 ,在本试验条件下 ,淋洗液中均含有一定数量的可溶性有机态N ,因此进行氮素矿化研究时 ,同时测定NH4-N、NO3-N和Norg的含量是必要的。 35℃下 ,N0 占全氮的比例为 7.23%～17.36% ,变异系数30.4% ;易矿化有机态氮占全氮的比例为0.27%～0.48% ,变异系数 200% ;碱解氮占全氮的比例为 5.55%～6.54% ,变异系数仅 5.8% ;微生物氮占全氮的比例在 2.16%～5.18%之间 ,变异系数28.8%。从几种指标测得的平均值看 ,N0碱解氮 微生物氮 易矿化氮 ,而变异系数是N0微生物氮 易矿化氮 碱解氮。虽然N0的绝对值远高于田间实际矿化量 ,     

应用几种植物物质及化合物抑制土壤脲酶活性和提高植物尿素氮的回收率

Effects of residues of 9 plants, lemon eucalyptus (Eucalyptus citriodora Hook., P1), robust eucalyptus (E. robusta Smith, P2), Nepal camphortree (Cinnamomum glanduliferum (Wall.) Nees, P3), tea (Camellia sinensis (Linn.) O. Ktze. f., P4), oleander (Nerium indicum Mill, P5), rape (Brassica campestris L., P6),Chinese tallow tree (Sapium sebiferum L., P7), tung (Vernicia fordii (Hemsl.), P8), and croton (Croton tiglium L., P9), 7 chemicals, boric acid (C1), borax (C2), oxalic acid (C3), sodium oxalite (C4), sodium dihydrogen phosphate (C6), sodium silicate (C7) and sodium citrate (C8), and a natural organic substance,humic acid (C5), on urease activity of a neutral purple soil and recovery of urea nitrogen by maize were studied through incubation and pot experiments. Hydroquinone (HQ) was applied as the reference inhibitor. After incubation at 37 ℃ for 24 h, 7 inhibitors with higher ability to inhibit urease activity were selected and then incubated for 14 days at 25 ℃. Results of the incubation experiments showed that soil urease activity was greatly inhibited by them, and the inhibition effect followed an order of P2＞P4＞C3＞C2＞P3＞C1＞HQ＞P1.The 7 selected materials reduced the accumulative amounts of N released from urea and the maximum urease activity by 11.7%～28.4% and 26.7%～39.7%, respectively, and postponed the N release peak by 2～4 days in the incubation period of 14 days under constant temperature, as compared to the control (no inhibitor).In the pot experiment with the 7 materials at two levels of addition, low (L) and high (H), the C1 (H), C3(H), C1 (L), P4 (L) and C2 (L) treatments could significantly increase the dry weights of the aboveground parts and the total biomass of the maize plants and the apparent recovery rate of urea-N was increased by 6.3%～32.4% as compared to the control (no hibitor).