Direct expression of an index for the degree of humification of humic acids using organic carbon concentration

Ikeya, Kosuke; Watanabe, Akira

doi:10.1080/00380768.2003.10409978

Cited by 74 publications

(80 citation statements)

References 22 publications

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“…An increase in the A 600 /C value and a decrease in the log (A 400 /A 600 ) value indicate an increase in the degree of humification of HA (Ikeya and Watanabe 2003). The degree of humification used here is synonymous with the degree of darkening (Kumada 1987;Ikeya and Watanabe 2003).…”

Section: Humification Degrees Of the Fractionsmentioning

confidence: 99%

“…The absorbances at 400 and 600 nm were immediately determined using a V-630 spectrophotometer (JASCO Corp., Tokyo, Japan). For the analysis of total organic C, the same solutions as those used for the absorbance measurements were mixed with four times the volume of 0.067 M potassium dihydrogen phosphate (Ikeya and Watanabe 2003), vortexed and then allowed to stand at room temperature overnight to remove inorganic C. The total organic C concentration of the mixture was determined using a total organic C analyzer (TOC-V E ; Shimadzu Co., Ltd., Kyoto, Japan). The degree of humification of the HAs was evaluated from the A 600 /C and log (A 400 /A 600 ) values, where A 400 , A 600 and C are the absorbances at 400 and 600 nm and the C concentration (mg mL −1 ), respectively (Ikeya and Watanabe 2003).…”

Section: Evaluation Of Humification Degreementioning

confidence: 99%

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Fractionation of soil humic acids by preparative polyacrylamide gel electrophoresis in the presence of concentrated urea

Karim

Aoyama

2013

Soil Science and Plant Nutrition

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To separate soil humic acids (HAs) into their constituents and characterize them, polyacrylamide gel electrophoresis (PAGE) was carried out in the presence of 7 M urea using a preparative electrophoresis system. Two types of soil HAs were fractionated into nine fractions by PAGE. The dark-colored constituents were recovered from the electrophoretic fractions by precipitation on acidification, and the brown-colored constituents dissolved in the acidic solution of fast-moving fractions were recovered by adsorption onto DAX-8 resin. High-performance size-exclusion chromatography (HPSEC) confirmed that the constituents of the HAs were separated based on their molecular size by PAGE. The dark-colored constituents exhibited higher degrees of humification than did the corresponding unfractionated HAs, except for the constituents remaining in the electrophoretic gels at the end of electrophoresis. Diffuse reflectance infrared spectroscopy revealed that the chemical properties of the dark-colored constituents changed regularly: the content of carboxyl groups decreased and the proportions of proteinous, aliphatic and polysaccharide moieties increased with increasing molecular size. The humification degrees of the constituents adsorbed onto DAX-8 resin were considerably lower than those of the corresponding unfractionated HAs. The chemical properties of the DAX-8-adsorbed constituents were different from those of the dark-colored constituents. Observation of electrophoretic fractions under blue light (470 nm) and HPSEC with fluorescence detection at an excitation wavelength of 460 nm and an emission wavelength of 520 nm showed that green fluorescent substances were largely concentrated in the smallest molecular size fractions and were partitioned into both the dark-colored precipitates and DAX-8-adsorbed fractions. The proportion of organic carbon recovered by precipitation and adsorption onto DAX-8 resin was 45-63%, indicating that substantial parts of the HA constituents were missing. The unrecovered constituents were considered to be acid-soluble, nearly colorless substances. The dissociation of the acid-soluble constituents from the acid-insoluble dark-colored constituents during the preparative PAGE of soil HAs was ascribed to disruption of hydrogen bonding and hydrophobic interactions caused by concentrated urea.

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Section: Humification Degrees Of the Fractionsmentioning

confidence: 99%

Section: Evaluation Of Humification Degreementioning

confidence: 99%

Fractionation of soil humic acids by preparative polyacrylamide gel electrophoresis in the presence of concentrated urea

Karim

Aoyama

2013

Soil Science and Plant Nutrition

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“…An increase in the A 600 /C value and a decrease in the log(A 400 /A 600 ) value were known to indicate an increase in the degree of humification of HA [15]. The degree of humification used here is synonymous with the degree of darkening [15,20]. Kumada [20] classified HAs into four types according to their optical properties: type A HAs are the most humified, type B HAs are the intermediates between type A and type Rp, type Rp HAs are the least humified, and type P HAs are moderately humified, as indicated in Fig.…”

Section: Humification Degree Of the Fractionsmentioning

confidence: 99%

“…2). An increase in the A 600 /C value and a decrease in the log(A 400 /A 600 ) value were known to indicate an increase in the degree of humification of HA [15]. The degree of humification used here is synonymous with the degree of darkening [15,20].…”

Section: Humification Degree Of the Fractionsmentioning

confidence: 99%

“…For the precipitated fraction, 1 mg of the freeze-dried sample was dissolved in 800 μL of 0.1 M NaOH and a part of the solution was mixed with four times the volume of 0.067 M potassium dihydrogen phosphate [15], vortexed, and then allowed to stand at room temperature overnight to remove inorganic carbon. The total organic carbon concentration of the mixture was determined using a total organic carbon analyzer (TOC-V E ; Shimadzu Co., Ltd., Kyoto, Japan).…”

Section: Determination Of Organic Carbonmentioning

confidence: 99%

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Separation of acid-soluble constituents of soil humic acids by dissolution in alkaline urea solution and precipitation with acid

Aoyama

2015

Chem. Biol. Technol. Agric.

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Background: Humic substances are considered to be composed of relatively small, heterogeneous molecules bound by weak linkages. The dissociation of acid-soluble constituents from soil humic acids (HAs) during the preparative polyacrylamide gel electrophoresis in the presence of concentrated urea has been previously demonstrated. Moreover, the dissociation of acid-soluble constituents has been attributed to the action of concentrated urea. The aim of this study was to investigate the effects of concentrated urea on the dissociation of acid-soluble constituents of soil HAs. Results: Three types of soil HAs were solubilized in 0.1 M NaOH containing 7 M urea and precipitated after 16 h by acidifying the samples to pH 1.0. The acid-soluble constituents were separated from the dark-colored precipitates by concentrated urea treatment and accounted for 16-45 % of the total organic carbon in HAs. Approximately half of the acid-soluble constituents was recovered in the DAX-8-adsorbed fraction. The humification degree of the DAX-8-adsorbed fraction was considerably lower than that of the corresponding unfractionated HA. In contrast, the humification degree of the precipitated fraction increased due to the separation of acid-soluble constituents. The molecular sizes of the DAX-8-adsorbed and DAX-8-non-adsorbed fractions, estimated by high-performance size exclusion chromatography, were similar and smaller than the precipitated fraction. Three-dimensional excitationemission matrix fluorescence spectroscopy revealed that the acid-soluble constituents exhibited fluorescence similar to that of fulvic acid (FA), added to which the DAX-8-non-adsorbed fraction exhibited protein-like fluorescence. Diffuse reflectance infrared Fourier transform spectroscopy showed that the DAX-8-adsorbed fraction contained proteinous moieties and the DAX-8-non-adsorbed fraction was rich in proteinous and polysaccharide moieties.

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Stability of soil organic matter accumulated under long‐term use as a rice paddy

et al. 2016

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To understand the mechanism responsible for the enhanced accumulation of soil organic matter (SOM) under long-term use as a rice paddy, soil samples from the plow layer from 16 fields that have been used for irrigated rice production from 5 to 2000 years in the Hangzhou Bay, China, were analyzed. The humin in silt/clay particles was isolated as a representative relatively stable SOM pool, and isotopic signatures (δ 13 C, δ 15 N, and 14 C concentration), 13 C nuclear magnetic resonance (NMR) spectra, and biodegradability in an incubation were examined. The amounts of C and N in the bulk soil, silt/clay, and silt/clay-humin increased with increasing period of use as a rice paddy within the east and west zones, respectively. The degree of humification determined for humic acids indicated that the progression of humification did not contribute to the accumulation of C beyond 100 years. The δ 15 N of silt/clay-humin suggested an increase in organic N derived from chemical fertilizer or recent biological fixation with increasing amount of this fraction. The 14 C concentration showed a negative correlation with the amount of silt/clay-humin C. The structural property with regard to 13 C NMR spectra and biodegradability of the silt/clay-humin remained constant with the length of use as a rice paddy or 14 C concentration. These results suggest that the larger C or N accumulation in the soils with a longer rice paddy history can be attributed to an enhancement in the accumulation of recently generated SOM rather than the stable accumulation of humus over the years.

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Direct expression of an index for the degree of humification of humic acids using organic carbon concentration

Cited by 74 publications

References 22 publications

Fractionation of soil humic acids by preparative polyacrylamide gel electrophoresis in the presence of concentrated urea

Fractionation of soil humic acids by preparative polyacrylamide gel electrophoresis in the presence of concentrated urea

Separation of acid-soluble constituents of soil humic acids by dissolution in alkaline urea solution and precipitation with acid

Stability of soil organic matter accumulated under long‐term use as a rice paddy

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