Extractable Soil Organic Matter Research Articles

Effects of soil organic matter extracted from soil on acid phosphomonoesterase

Extract of soil organic matter (SOM) at concentrations of 0.05, 0.5, 2.5, 5 and 50 mg l −1 inhibited commercial acid phosphomonoesterase activity by 10.5, 13.3, 65.5, 77.2 and 89.3%, respectively. The inhibition was not due to adsorption of the product, because p-nitrophenol was not adsorbed on the SOM extract. At concentrations of 0.05 and 0.5 mg l −1 the SOM extract affected the enzyme kinetics considerably: apparent K m increased significantly, from 1.76 to 2.15 and 3.94 m m, respectively, but V max changed only slightly. With higher concentrations of the SOM extract (2.5–50 mg l −1) the reaction no longer followed Michaelis-Menten kinetics. The observed interaction with SOM and acid phosphomonoesterase might be ecologically interesting, especially in soils with high SOM concentrations, because of the importance of phosphomonoesterases in the mineralization of organic P esters in soils and rhizospheres.

Arylsulfatase activity in soil and soil extracts using natural and artificial substrates

The arylsulfatase activity of soil and humic arylsulfatase complexes extracted from soil were measured using the substrates p-nitrophenyl sulfate and low molecular weight (500–10000) soil ester sulfate compounds. Soil samples from the Aphorizon of a Podzol from S-amended wheat plots and a Regosol from dykeland hayfield plots were investigated. Soil arylsulfatase activity (assayed with p-nitrophenyl sulfate) in the fall was significantly higher than spring samples; however, no seasonal differences were observed when humic-arylsulfatase complexes were assayed with p-nitrophenyl sulfate. The discrepancy between arylsulfatase activity in soil and soil extracts was probably due to inhibitors which were found in soil materials. These results appear to support the theory that abiotic arylsulfatase is a relatively stable and persistent component of soil. There was a marked difference in the response by humic-arylsulfatase complexes to the artificial substrate p-nitrophenyl sulfate and natural low molecular weight soil substrates. Humic-arylsulfatase complexes hydrolysed 35–80% of added low molecular weight substrates depending on the treatment. The molecular size, concentration, and chemical composition of the low molecular weight ester sulfate compounds affected hydrolysis of the low molecular weight substrates. The response by humic-arylsulfatase complexes to the chromogenic ester sulfate, p-nitrophenyl sulfate did not reflect the ability of these complexes to hydrolyse natural soil substrates. In an experiments we examined arylsulfatase activity and soil S status in relation to the total S in plant tissue and grain from wheat plants grown in the Podzol. Tissue S was more strongly associated with soil S than the wheat grain. Hydriodic acid-S, Ca(H2PO4)2-extractable sulfate, and hydrolysable ester sulfates in the high molecular weight (>10000) and low molecular weight (500–10000) fractions of soil organic matter extracts were strongly positively correlated with tissue S. Arylsulfatase activity in soil and humic-arylsulfatase extracts assayed with p-nitrophenyl sulfate were also strongly correlated with tissue S, while humic-arylsulfatase activity assayed with the low molecular weight substrate was negatively correlated with tissue S.

Physical protection of soil organic S studied by extraction and fractionation of soil organic matter

Physical protection of soil organic S may, in part, be responsible for the constraints on the ability of soils to supply S to plants. We investigated the short-term cycling of S into soil organic matter fractions protected by soil structure or by the nature of the organic compounds. Organic S fractions were labelled by incubation with carrier-free 35S, and then extracted by aqueous acetylacetone, with or without ultrasonic dispersion of the soil. The extracted organic S was fractionated according to molecular weight (MW) using gel permeation chromatography. It was found that soil dispersion increased the amount of extractable S by 1.6 – 3.3 times, suggesting a large part of organic S was physically protected inside aggregates. Turnover of S in the protected fraction was slow, as illustrated by low incorporation of 35S during incubation. The main part of the soil organic S was present in either very large organic matter molecules (MW > 100,000 Da) or in small molecules (700–5000 Da). During the 8-wk incubation, 35S was initially incorporated into the MW < 700 Da fraction and then recycled into the 700–5000 Da fraction. Little S-cycling was evident in fractions >5000 Da, and it is concluded that physical protection of organic S was caused by both the nature of the organic compounds and by association with clay in soil aggregates.

Characterization of ester sulphate in a gypsum-amended podzol using an immobilized sulphatase reactor

An immobilized sulphatase reactor column was successfully used to determine the biochemical stability of ester sulphate in soil organic matter extracted from a podzol amended with gypsum. The sulphatase from Helix pomatia was covalently attached to controlled-porosity glass beads, and the immobilized enzyme was packed into a small glass column. The optimum pH, the time required to reach equilibrium, and the percentage of substrate consumed for the enzymatic hydrolysis of soil ester sulphate (pH 7.7, 90 min, 23–59%) were substantially different from those of p-nitrophenyl sulphate at similar concentrations of substrate (pH 7.0, 40 min, 99%). The striking difference in the biochemical stability and kinetic behaviour between soil ester sulphate and the simple synthetic substrate reflected their different chemical nature and structural features. The amounts of enzymatically hydrolysable (labile) ester sulphate in soil organic matter extracted from the podzol amended with gypsum at rates of 0, 50, and 200 kg S ha-1 were significantly different (P=0.0004), being 0.5, 1.1, and 1.4 μg S ml-1 soil extract (or 5, 11, and 14 μg S g-1 soil), respectively. The labile ester sulphate was not correlated with the total hydriodic acid-reducible organic sulphate with the soil organic matter extracts but with the hydriodic acid-reducible organic sulphate: organic C ratio, which increased as a result of gypsum amendment. This study revealed that input of inorganic sulphate as gypsum substantially increased the accumulation of labile ester sulphate in a podzol.

A Robust Method for Estimating Soil Properties in Unsampled Cells

For site-specific crop management (SSCM), fields are viewed as collections of small regions (cells) in which soil properties are nearly uniform. A field information system (FIS) can be used to store soil fertility data and to create application rate maps on a cell-by-cell basis. A data blocking procedure was developed to convert soil sample data into a new data set in which one value represents the soil property in each cell. A nonparametric distance-weighting algorithm was developed which produced about the same estimation errors as a kriging method, but was much faster. Example applications of the data blocking procedure to KC1 extractable nitrate and soil organic matter data are included.

Labile ester sulphate in organic matter extracted from podzolic soils

We studied the effect of soil pretreatment, molecular-weight fractionation, and K2SO4 addition on the concentration and biochemical stability of ester sulphate in soil organic matter. A labile ester sulphate fraction (8.1 μg S g−1 soil) was detected in the organic matter extracted from a sulphate-rich podzolic sandy loam. This fraction was susceptible to loss during soil pretreatment with water and KCl solution and subsequent extraction of organic matter from the soil. The low-sulphate loam was low in labile ester sulphate (0.6 μg S g−1 soil) and the pretreatments had little effect. The addition of K2SO4 to the organic matter extracted from the low-sulphate soil resulted in the formation of appreciable amounts of labile ester sulphate. Newly formed ester sulphate tends to be biochemically less stable than indigenous ester sulphate in soil humic polymers and the ester sulphate associated with the low molecular-weight fractoin of soil organic matter appears to be more susceptible to loss by enzymatic hydroylsis. The results were interpreted in terms of steric effect. Ester sulphate groups bound to external surfaces of soil humic polymers may be easily accessible to sulphatase enzyme and thus readily mineralizable during incubation or extraction of soil organic matter at low soluble-sulphate levels. Sulphate groups on inner surfaces of the organic polymers are “shielded” from the enzyme due to size exclusion and hence more stable.

Enzymatic hydrolysis of ester sulphate in soil organic matter extracts

A method of assessing the enzymatic hydrolysis of ester sulphate in soil organic matter was developed. Soil organic matter extracted using a mild, chelating resin extraction procedure was incubated with a sulphatase from Helix pomatia in 0.05 M sodium acetate buffer (pH 4–8) at 37°C for 2h and the sulphate released was determined by a high performance liquid chromatography-conductivity detector system. The effect of some soil factors on the enzymatic hydrolysis of ester sulphate was examined. The study showed that part of the ester sulphate in soil organic matter was biochemically reactive. In the three Podzols studied, the ester sulphate hydrolysed accounted for 2%–12% of the hydriodic acid-reducible organic sulphate extracted. The largest amount of hydrolysable ester sulphate was found in the soil with a low pH, high inorganic sulphate and high hydriodic acid-reducible organic sulphate.

Extraction of newly immobilized 15n from an illinois mollisol using aqueous phenol

Studies were conducted on an 15N-enriched Illinois Mollisol (Flanagan silt loam) to determine the extractability of newly immobilized N with aqueous phenol (45%, v/v). In comparison to mild extradants proposed as indexes of plant available N (i.e. 10 mw NaHCO 3 and hot 10 m m CaCl 2), phenol showed the highest selectivity for the immobilized N, both with regard to the amount of biomass N extracted and the magnitude of the extractability ratio (ER). Aqueous phenol was also more selective in removing the immobilized N than reagents used for extraction of soil organic matter (i.e. 150 m m Na 4P 2O 7 and 100 m m KOH). Results with soils incubated for up to 120 days showed that the amount of 15N extracted with aqueous phenol fluctuated with time and was related to changes in the soil microbial population, e.g. ER was highest when the bacterial population was maximal. Aqueous phenol shows promise as a selective extradant of potentially-available (labile) organic N in soils.

Free and HF-HO-extractable amino acids determined by high performance liquid chromatography in a loamy sand soil

Amino acids were extracted from fertility plots of a loamy sand soil with 0.05 M HF-HCl and with a 10% ethanol solution (“free” amino acids) and analysed by reverse-phase high performance liquid chromatography (HPLC). The total quantities of amino-N compounds analysed were 4.4 μg/g soil for the acid treatment and 22.6 μg/g soil for the 10% ethanol extract. Glycine and glutamic acid were the most abundant of 15 amino-N compounds in the HF-HCl extracts, whereas glutamic acid and ornithine + NH+4 were found in the highest concentration in the 10% ethanol extracts. The HF-HCI pretreatment is used to increase the efficiency of the extraction of soil organic matter. Although this pretreatment removed some amino acids, the acids extract less than 1% of the total amino-N content of the crude soil extracts. The pretreatment, therefore, was not overly destructive. Comparisons between the amino acids extracted from the fertility plots were not conclusive, except for glycine, which was greater in concentration in the higher fertilizer N plots of the same crop rotation.

Extraction of soil organic matter by supercritical fluids

Extraction of soil organic matter by supercritical fluids

Extraction of soil organic matter under chemically mild conditions

Abstract Large additions of urea greatly increased the effectiveness of some chemically mild extractants of soil organic matter. Brief agitation with an ultrasonic disintegrator also enhanced the action of these mixed solutions. With a range of soils, 0.05M Na4P2O7 in 8M urea extracted at least as much soil carbon as 0.05M Na4P2O7 in 0.5M NaOH. A solution of 0.3M NaHCO3 in 8M urea usually extracts less carbon but introduces only Na+ as a mineral contaminant.

A PROCEDURE FOR THE CHARACTERIZATION OF SOIL ORGANIC MATTER

In a recent cooperative study, in which four laboratories participated, organic matter in a large number of Canadian soil samples was characterized by relatively simple methods. As result of this work we are proposing a procedure for the extraction, separation and characterization of soil organic matter. The procedure includes determinations of organic C and total N in initial soils, followed by the isolation from the soils of humic and fulvic acids. Total C and N and E4/E6 ratios are then determined in the latter fractions. From these data, proportions of extractable soil-C and soil-N and HA/FA ratios are computed.

APPLICATIONS OF NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY TO THE STUDY OF THE STRUCTURE OF SOIL ORGANIC MATTER

SummaryRecent developments in the application of nuclear magnetic resonance (n.m.r.) spectroscopy to soil science are reviewed. Progress in 1H, 13C and CP‐13C n.m.r. spectroscopy of humic substances is reported. Methods of determining the fraction of aromatic carbon in soil organic matter extracts are discussed, and methods by which structural group analysis can be carried out on in situ organic matter of whole soils are reviewed.

Enzymatic Activities and Extractable Organic Matter in Soils Invaded by Lycopodium tristachyum Fairy Rings

AbstractThe interaction of fairy rings of Lycopodium tristachyum Pursh. with the soil which they invade was examined by measurement of various soil enzymatic activities and extractable soil organic matter. The activities of cellulase, xylanase, inulinase, α‐galactosidase, invertase, peroxidase, chitinase, and polygalacturonase were enhanced in soil under the rings compared with soil just outside the rings. The activity of urease was lower under the ring while the activity of β‐glucosidase was unaffected. The amount of nitrogen, hexose, and phenolics extracted by 0.01M CaCl2 during autoclaving was enhanced in soil under the ring. The level of reducing substances extracted by dilute buffer and the optical density of buffered extracts were similarly elevated. Extractable lipid, humic acid, and β‐humus were independent of soil location. Significant correlations between some readily extractable organic components and the activities of chitinase, invertase, xylanase, and α‐galactosidase in the soil were observed.

REACTIONS BETWEEN METALS AND HUMIFIED ORGANIC MATTER

SummaryWe studied the properties of the soluble and dispersed compounds of Cu, Mn, Co, Ni, Pb, Zn, and Cd formed by the action of aerobically decomposing plant matter on the respective metal oxides. The metals were mobilized partly in association with colloidal humified organic matter, and partly in true solution as complexes that seemed to be anionic.In the presence of a clay soil there was no net mobilization of colloidally bound Cu, but the dialysable Cu complex was not appreciably sorbed by the mineral colloids and was leached from the reaction mixture.The metals were not precipitated under alkaline conditions from the dialysable complex forms. Material with similar complexing properties was found in the dialysable fractions of a soil organic matter extract, of water squeezed from a raw peat, and of laboratory lysimeter solutions from a podzol under Calluna.Below about pH 6 the exchange of Cu on a soil clay was not affected by the presence of colloidal decomposition products of lucerne. With Co, Ni, and Zn the corresponding pH value was about 4, and the critical value for Cu in the presence of colloidal soil organic matter was also about 4. Below these values the metal and organic matter sorption curves were diametrically opposed so that under these conditions Cu is apparently not strongly bonded to colloidal organic matter.

INFLUENCE OF EXTRACTED ALUMINUM ON ORGANIC MATTER FRACTIONATION IN SOILS DERIVED FROM VOLCANIC ASH

The presence of humic acid B fraction in alkaline extracts of volcanic ash-derived soils (high in reactive aluminum) was studied. The humic acid B does not exist as defined organic matter in these soil extracts. Its formation as an insoluble fraction at pH 4.8 is due to an Al(OH)3 gelatin precipitate formation which adsorbs onto its surface the soluble fulvic acid fraction. The phosphate extracted by the alkaline extractant would be adsorbed on the Al(OH)3 surface in a similar way. The artificial formation of the so-called HA-B is easily avoided by eliminating the Al ions of the acid organic matter solution by means of a cation exchanger. In this way the extracted soil organic matter can be fractionated only into two really different fractions according to their solubility in alkaline or acid medium: humic and fulvic acids.

Effect of chelation on the toxicity of aluminum

Maize seedlings with roots exposed to solutions of Al complexed by citrate, EDTA, or soil organic matter extract, were not significantly different in appearance, yields, or chemical analyses of their tops from plants not receiving Al. In contrast were plants treated with ionic hydroxy Al in the same concentrations. Roots were severely injured and their yields and Ca and Mn contents depressed; yields and P, Ca, and Mn contents of tops also were lowered. Translocation of Al to tops was negligible with chelation.

CHEMICAL PROPERTIES OF ORGANIC MATTER EXTRACTED FROM A NUMBER OF Ah HORIZONS BY A NUMBER OF METHODS

The organic matter of eight Ah horizons, representing four soil Orders, was extracted and purified by a number of procedures, all designed to extract humic acid or high-molecular weight complexes. Organic carbon and total nitrogen contents of the air-dried soils were determined. The humic substances extracted from the soil were analyzed for carbon, nitrogen, total and carboxyl acidity, and ash and a number of its constituents. The nitrogen content and carboxyl acidity of the humic acids as well as the soluble silicon, calcium, and phosphorous content of the ash varied with the method used to extract the humic substances. The extraction of soil organic matter from Ah horizons by chelating resins merits pursuance. Often, high carboxyl acidities, as confirmed by infrared spectra, existed notwithstanding high ash contents. Other criteria, such as nitrogen content of the humic substances, may also have to be considered in this ash–carboxyl acidity relation. The materials extracted from the Lithic Regosol had relatively high calcium contents, low nitrogen and ash contents, and high calcium content of the ash, as compared with the other seven soils, regardless of method. With two methods total acidity was also high.

Heterotrophic nitrification in soils— a preliminary investigation

Isolates of heterotrophic organisms from a Teak soil were tested for their ability to produce nitrite and/or nitrate in a glucose-peptone medium, soil organic matter extract, and in sterilized soils. The amounts of nitrite and nitrate formed varied with the medium used. The ability to produce nitrite and/or nitrate was more common and more efficient among the fungi where up to 4.76 ppm nitrite-nitrogen and 12.88 ppm nitrate-nitrogen were obtained after 14 days incubation.

Organic Phosphorus and Inositol Phosphates in Molecular Size Fractions of a Soil Organic Matter Extract

AbstractSoil organic matter extracted with the chelating resin Dowex A‐1, was fractionated into three fractions on a column of Sephadex G‐75. The first fraction, which has an approximate lower molecular weight limit of 50,000, contained 36% of the total organic P in the extract. The second fraction, with intermediate molecular weights in the range 1,000–50,000, contained 31% of the P. The third fraction, which was considered below the fractionation range and therefore is below 1,000 molecular weight, contained 7.8% of the organic P in the extract. Inositol phosphates were detected in the second and third fractions but not in the first fraction. Inositol phosphates in the third fraction were considered to be in the free form, while those in the second fraction must be in either a polymer form or bound to other organic compounds.