Changes in Physical Properties of Chernozems under the Impact of No-Till Technology

Eurasian Soil Science - This article presents the results of research on the impact of no-till technology on the natural bulk density and macro- and microaggregate composition of the topsoil...     

Optical Properties of the Extractable Organic Matter Fractions in Typical Chernozems of Long-Term Field Experiments

Eurasian Soil Science - The extractable fractions of organic matter (OM) differing in their mobility—water-extractable organic matter, labile humic substances, and humic substances—have...     

Copper(II) binding by free and kaolinite-sorbed humic substances

Humic preparations isolated from different sources—soils (a soddy-podzolic soil and a typical chernozem), high-moor peat, and brown coal—have been used. To analyze the binding of copper ions by humic substances (HSs), the preparations were obtained in two forms: solutions and humic-clay complexes (HSs irreversibly sorbed on kaolinite). With this approach, the binding of copper(II) ions by HSs has been studied in different systems: (1) Cu(II)-HSs irreversibly sorbed on kaolinite, (2) Cu(II)-dissolved HSs, and (3) Cu(II)-dissolved HSs-HSs irreversibly sorbed on kaolinite. In the systems containing both dissolved HSs and humic-clay complexes, HSs of similar structure isolated from the same source were used. The quantitative estimation of the copper binding was based on the constant of sorption (K) for HSs in humic-kaolinite complexes and the stability constant (β) of complexes for free (dissolved) substances. Both parameters were expressed in similar units: L/kg. The values of logK = 3.31—3.33 are independent of the quantity and quality of the HSs in the sorption complexes but reliably exceed the K value for pure kaolinite (2.92). The value of β is not affected by the presence of insoluble HSs together with their soluble forms, but it depends on the source of HSs. The value of logβ varies in the range from 5.62 to 6.93, which significantly exceeds K and indicates a significantly higher affinity of dissolved HSs for copper ions than that of irreversibly sorbed HSs. The revealed regularities have shown that the content of HSs in the soil solution can significantly affect the mobility of a heavy metal bound to the soil organic matter.     

Heterogeneity of Organic Matter of Aggregates of Protocalcic Chernozems

Eurasian Soil Science - Layers were step-by-step removed from macroaggregates (2–1 mm in diameter) of Protocalcic Chernozems via successive abrasion in a revolving rotator during 5, 10, 15,...     

Methodological Aspects of the Determination of Fatty Acids in Soil by Thermochemolysis

Eurasian Soil Science - Fatty acids (FAs) are among the most informative parts of nonspecific soil organic matter). Their composition and content reflect the specific features of many soil...     

Contents of Organic Carbon and Nitrogen in Particle-Size Fractions of Aggregates of Typical Chernozems (Protocalcic Chernozems)

Eurasian Soil Science - Specific features in the content and accumulation of organic carbon and nitrogen in the aggregates of typical chernozems (Protocalcic Chernozems) of long-term experimental...     

Changes in the Ratio of Aggregate Fractions in Humus Horizons of Chernozems in Response to the Type of Their Use

Eurasian Soil Science - Data on the aggregate-size distribution (dry sifting method) in humus horizons of chernozems were processed by principal components analysis (PCA) with the centered logratio...     

Enzymatic activity inside and outside of water-stable aggregates in soils under different land use

A method is presented for assessing the distribution of enzymatic activity inside and outside of water-stable aggregates. Two samples of water-stable aggregates >1 mm have been isolated from dry aggregates of 1–2 mm. To determine the enzymatic activity, a substrate has been added to one of the samples without disaggregation; the other sample has been preliminarily disaggregated. Enzymatic activity within waterstable aggregates has been assessed from the difference between the obtained results under the supposition that the penetration of substrate within the water-saturated aggregates is hampered, and enzymatic reactions occur only at the periphery. The levels and distributions of enzymatic (peroxidase, polyphenol oxidase, and catalase) activities in water-stable aggregates of soddy-podzolic soils under forest and plowland and typical chernozems of long-term field experiments have been studied. The peroxidase, polyphenol oxidase, and catalase activities of water-stable aggregates vary from 6 to 23, from 7 to 30, and from 5 to 7 mmol/(g h), respectively. The ratio between the enzymatic activities inside and outside of soil aggregates showed a higher dependence on soil type and land use, as well as on the input of organic matter and the structural state, than the general activity level in water-stable aggregates.     

Irreversible sorption of humic substances causes a decrease in wettability of clay surfaces as measured by a sessile drop contact angle method

Purpose

The objective of the study was to obtain quantitative assessments of the hydrophobic impact of irreversible sorption of humic substances (HSs) onto clay mineral surfaces using a sessile drop contact angle method.

Materials and methods

Two clays (kaolin and montmorillonite) were modified with four humic materials: (1) sod podzolic soil, (2) chernozem, (3) peat, and (4) coal (leonardite). The humic materials were characterized using elemental analysis, size exclusion chromatography, and ¹³C NMR spectroscopy. Both clay samples were saturated with Ca²⁺ prior to modification with HS using a sorption isotherm technique. Contact angles (CAs) of the obtained HS-clay complexes were determined using a static sessile drop method after drying the obtained HS-clay complexes in the form of a thin film.

Results and discussion

HS modification rendered both clays under study—kaolin and montmorillonite—more hydrophobic. In case of Ca-kaolin, the CA values increased from 27° (Ca-kaolin) up to 31°–32° (all HS-kaolin complexes) with no significant difference among the HS types used for modification. In the case of Ca-montmorillonite, the CA values increased from 41° (Ca-montmorillonite) up to 51°–83° with the following ascending trend for the humic types investigated: chernozem HS < coal HS < peat HS < sod-podzolic HS. This trend is in reverse to the degree of aromaticity of the HS, expressed as the content of aromatic carbon, and it is directly proportional to the molecular weight of each HS.

Conclusions

Application of a sessile drop method showed increased surface hydrophobicity of HS-modified clays. Much more substantial hydrophobization was observed for montmorillonite as compared to kaolin, which was explained by the differences in the sorption mechanism.