Nature-inspired soluble iron-rich humic compounds: new look at the structure and properties

Purpose

Humic substances (HS) being natural polyelectrolyte macromolecules with complex and disordered molecular structures are a key component of the terrestrial ecosystem. They have remarkable influence on environmental behavior of iron, the essential nutrient for plants. They might be considered as environmental friendly iron deficiency correctors free of synthetic iron (III) chelates disadvantages. The main goal of this study was to obtain water-soluble iron-rich humic compounds (IRHCs) and to evaluate their efficiency as chlorosis correctors.

Materials and methods

A facile preparation technique of IRHCs based on low-cost and available parent material was developed. The iron-containing precursor (ferrous sulfate) was added dropwisely into alkaline potassium humate solution under vigorous stirring and pH-control. A detailed characterization both of organic and inorganic parts of the compounds was provided, the iron species identification was carried out jointly by EXAFS and Mössbauer spectroscopy. Bioassay experiments were performed using cucumber Cucumis sativus L. as target plants. Plants were grown in modified Hoagland nutrient solution, prepared on deionized water and containing iron in the form of IRHCs. Total iron content in dry plants measured by spectrophotometry after oxidative digestion and the chlorophyll a content determined after acetone extraction from fresh plant were used as parameters illustrating plants functional status under iron deficiency condition.

Results and discussion

The high solubility (up to130 g/l) and iron content (about 11 wt%) of the IRHCs obtained allow considering them to be perspective for practical applications. A set of analytical methods has shown that the main iron species in IRHCs are finely dispersed iron (III) oxide and hydroxide nanoparticles. An application of the precursor solution acidification allows to obtain compounds containing a significant part of total iron (up to 30 %) in the form of partly disordered iron (II–III) hydroxysulphate green rust GR(SO₄ ^2?). Bioavailability of iron from IRHCs was demonstrated using bioassay in cucumber plants grown up on hydroponics under iron deficiency conditions.

Conclusions

The application of iron oxides chemistry for humic substance containing solution was proved to be an effective approach to synthesis of IRHCs. Using bioassay on cucumber plants C. sativus L. under iron deficiency conditions, the efficiency of compounds obtained as chlorosis correctors was demonstrated. Application of water-soluble IRHCs led to significant increase of chlorophyll a content (up to 415 % of the blank) and iron content in plants (up to 364 % of the blank) grown up on hydroponics.     

Thermodynamic analysis of the effect of strongly swelling polymer hydrogels on the physical state of soil and sediment samples

The effect of five Russian and foreign hydrogels on the water retention curve (WRC) and the related physical parameters of soils and sediments differing in their genesis and degree of dispersion has been considered on the basis of a proprietary version of the equilibrium centrifugation method. The new version of the method with the use of a high-speed centrifuge has allowed obtaining WRC in a wide range of matric potentials from 0 to 3000 J/kg (pF = 4.5) with the experimental estimation of almost all the soil-hydrological constants. The first analysis of strongly swelling polymer hydrogels (SSPHs) on WRC and the structural curves of the pore size distribution in heavy-textured soils has been performed, and the possibility has been shown of increasing their water capacity at the swelling of SSPHs in the region near water saturation. The most efficient is the use of SSPHs in light soils, which allows their water retention to be brought to the level of native loamy sands and loams in the SSPH content range of 0.1–0.3% of the enclosing coarse material. The best characteristics were observed for the Russian hydrogel VUM developed by the Institute of Technical Chemistry of the Urals Branch of the Russian Academy of Sciences and produced by the Urals Plant for Chemical Reagents.     

Soils of the Istra River valley within the New Jerusalem monastery and its surroundings

The paper studies the soils of the New Jerusalem monastery complex, which covers a vast area in the Istra River valley and has been significantly changed since the foundation of the monastery (in 1656). The main types of anthropogenically transformed and natural soils are identified; their morphological peculiarities and physical and chemical properties are characterized. The regularities of the spatial soil distribution, which are determined by both natural and anthropogenic factors, are ascertained. The results of the study can be used in implementing the restoration of the monastery and reconstruction of the historical landscape.     

Discrimination between orange juice and pulp wash by (1)H Nuclear Magnetic Resonance spectroscopy: identification of marker compounds

The potential of NMR spectroscopy and multivariate analysis methods to detect the adulteration of orange juice with pulp wash is demonstrated. Principal component analysis has been applied to (1)H NMR spectra of >300 orange and pulp wash juices, and stepwise linear discriminant analysis was used to classify the samples. A model with six principal components gave a high success rate of classification (94%) for both training and validation sets. An important principal component loading showed that dimethylproline played a key role in the discrimination between the two types of juice, with higher levels in pulp wash. Dimethylproline was not previously known as a marker compound for orange juice adulteration. An ANOVA test revealed at least 21 other NMR signals that differed significantly between the authentic and pulp wash groups. The compounds they represent could be seen as potential marker compounds in addition to dimethylproline. This makes NMR with chemometrics an attractive screening tool with advantages in terms of rapidity, simplicity, and diversity of information provided.     

Speciation of Selected Minor and Major Elements in Oil Ash I. Operationally Defined Chemical Associations and Aqueous Speciation

This study is focused on the speciation of selected elements in oil ash. Our efforts were directed primarily to obtain information on the various forms of vanadium, chromium and nickel. One sample was characterized via its total composition and via its capacity for releasing various elements. The latter was estimated by hot water and nitric acid extractios. A rapid cold water extraction technique has been developed and utilized for sample preparation prior to aqueous speciation by high pressure ion chromatography (HPIC). Results of the HPIC measurements, in agreement with electron spin resonance (ESR) investigations performed on the solid sample, indicate that 38% of the vanadium is present as VOSO₄, 58% of the chromium is Cr₂(SO₄)₃ and 30% of the nickel is NiSO₄. The pH and the redox potential values of the cold water extract support the existence of these forms. Results of a generic study with successive fractionation extractions show the probable existence of oxides, associations with organic matter and aluminosilicate minerals.     

Characterization of pine nuts in the U.S. market, including those associated with "pine mouth", by GC-FID

Taste disturbances following consumption of pine nuts, referred to as "pine mouth", have been reported by consumers in the United States and Europe. Nuts of Pinus armandii have been associated with pine mouth, and a diagnostic index (DI) measuring the content of Δ5-unsaturated fatty acids relative to that of their fatty acid precursors has been proposed for identifying nuts from this species. A 100 m SLB-IL 111 GC column was used to improve fatty acid separations, and 45 pine nut samples were analyzed, including pine mouth-associated samples. This study examined the use of a DI for the identification of mixtures of pine nut species and showed the limitation of morphological characteristics for species identification. DI values for many commercial samples did not match those of known reference species, indicating that the majority of pine nuts collected in the U.S. market, including those associated with pine mouth, are mixtures of nuts from different Pinus species.     

The Influence of Vegetation on the Forest Soil Properties in the Republic of Karelia

Eurasian Soil Science - The effect of vegetation on soil properties (acidity, C/N ratio, content of exchangeable nutrients) was assessed for the northern and middle taiga forests in the Republic of...     

Effect of Compost-Fertilizer Combinations on Wheat Yields

Combining composts made from industrial wastes with fertilizer in amounts to equal the N requirement of wheat (Triticum aestivum L.) was done with the purpose of determining the effect of such mixtures on yield and N content. Composts made from jute mill waste (JMW) or from sugar mill wastes (SIW) were mixed with fertilizer in a loam soil so that 0, 25, 50, or 100% of the N was supplied by the compost. Each treatment except the control received the equivalent of 125 kg N/ha and 75 kg P/ha. Wheat, variety Pb 81, was grown for 6 months. The 50% compost:50% fertilizer combinations were equal to or better than the 100% complete fertilizer treatment in terms of grain yield. The synergistic response from the compost-fertilizer treatment may have been the result of other ingredients in the compost such as micronutrients or organic matter. These data demonstrate that composts can substitute for a portion of mineral fertilizer which may result in a savings for farmers.