Preparation and characterization of model humic polymers containing organic phosphorus

The nature of organic P in soil organic matter was studied by evaluating the incorporation of serine, phosphoserine, ethanolamine, phosphoethanolamine and glycerophosphate into model humic polymers prepared by chemical oxidation of polyphenols. Elemental and functional group analysis indicated that the composition of model humic polymers ranged as follows: organic C, 50.6–56.8%; total acidity, 7.86–11.87m-equiv g^?1; carboxyl, 1.42–2.00 m-equiv g^?1; total hydroxyl, 6.79-10.0 m-equiv g^?1; ash, 6.4–13.9%; E₄/E₆ ratio, 5.34–6.19; organic N, 0.70–1.65% and organic P, 0.254–0.942%. These values are within the ranges reported for soil humic substances. The only non-phenolic compounds incorporated into model humic polymers were those containing free amino groups. The P content of model polymers was not increased by the presence of KH₂PO₄, glycerophosphate, serine or ethanolamine whereas phosphoserine and phosphoethanolamine resulted in model polymers containing 0.254 and 0.942% P, respectively. Further characterization studies of the model polymer containing phosphoethanolamine (HA-PE) showed that most of the C (83.2%), N (79.8%) and P (75.3%) was in the humic acid fraction. Gel filtration of HA-PE showed that 0.5% of the polymer was present in high molecular weight (mol. wt) components (mol. wt > 100,000) and 74.8% of the polymer was in two components of mol. wt 10,000–50,000. The majority of the organic P in HA-PE was associated with the medium molecular weight fractions (79.2%) while 16.8% of the P was associated with materials possessing mol. wt < 10,000. Attempts to demonstrate the presence of organic P functional groups contained in HA-PE by infrared spectroscopy was limited by the relatively small amounts of organic P incorporated into the model humic polymers. The results obtained show that a portion of the unidentified organic P in soil humic substances may arise from the incorporation of organic compounds containing both amino and phosphate ester functional groups during oxidative polymerization of polyphenols.     

The distribution of nitrogen in some highly organic tropical volcanic soils

The qualitative and quantitative distribution of N-compounds in 10 tropical soils, and in a number of humic materials extracted from representative samples thereof, was determined after 6 N HCl hydrolysis.Eighty to 98% of the total N in the soils and humic materials was hydrolysable by 6n HCl. Slightly less than one half the hydrolysable N in the soils and humic fractions consisted of amino acids. Well-drained soils and fulvic acids extracted from them contained unusually high concentrations of the acidic amino acids, aspartic and glutamic acids. Between 80 and 95% of the amino acids in the soils was accounted for in the humic materials + NaOH-insoluble organic residues. NH⁺₄-N released by acid hydrolysis was generally higher for the soil samples than for the humic materials. Amino sugar-N constituted relatively small proportions of the total N in the soils and humic fractions.Our data suggest that large quantities of amorphous allophanic materials coupled with relatively high enzymic activity are responsible for the observed accumulation of acidic amino acids in the well-drained tropical volcanic soils.     

Transformation of organic matter from maize residues into labile and humic fractions of three European soils as revealed by 13C distribution and CPMAS-NMR spectra

The dynamics of incorporation of fresh organic residues into the various fractions of soil organic matter have yet to be clarified in terms of chemical structures and mechanisms involved. We studied by ¹³C‐dilution analysis and CPMAS‐¹³C‐NMR spectroscopy the distribution of organic carbon from mixed or mulched maize residues into specific defined fractions such as carbohydrates and humic fractions isolated by selective extractants in a year‐long incubation of three European soils. The contents of carbohydrates in soil particle size fractions and relative δ¹³C values showed no retention of carbohydrates from maize but rather decomposition of those from native organic matter in the soil. By contrast, CPMAS‐¹³C‐NMR spectra of humic (HA) and fulvic acids (FA) extracted by alkaline solution generally indicated the transfer of maize C (mostly carbohydrates and peptides) into humic materials, whereas spectra of organic matter extracted with an acetone solution (HE) indicated solubilization of an aliphatic‐rich, hydrophobic fraction that seemed not to contain any C from maize. The abundance of ¹³C showed that all humic fractions behaved as a sink for C from maize residues but the FA fraction was related to the turnover of fresh organic matter more than the HA. Removal of hydrophobic components from incubated soils by acetone solution allowed a subsequent extraction of HA and, especially, FA still containing much C from maize. The combination of isotopic measurements and NMR spectra indicated that while hydrophilic compounds from maize were retained in HA and FA, hydrophobic components in the HE fraction had chemical features similar to those of humin. Our results show that the organic compounds released in soils by mineralization of fresh plant residues are stored mainly in the hydrophilic fraction of humic substances which are, in turn, stabilized against microbial degradation by the most hydrophobic humic matter. Our findings suggest that native soil humic substances contribute to the accumulation of new organic matter in soils.     

Soil enzymatic response to addition of heavy metals with organic residues

Changes in organic C, available P, available heavy metal contents and enzymatic activities induced by addition of two heavy metal rich organic residues [a municipal solid waste compost (MWC) and a non-composted paper sludge (PS)] were determined in two different soils during a 280-day incubation experiment. The addition of the organic materials caused a rapid and significant increase in the organic C and enzymatic activities in both soils, this increase was specially noticeable in soils treated with MWC. In general, enzymatic activities in amended soils tended to decrease with the time. Organic materials also increased heavy metal contents in soil. However, the presence of available soil heavy metals due to the addition of the organic materials at doses of 50,000 kg ha^-1 did not negatively affect dehydrogenase, #-glucosidase or urease activities in the soils. There were significant and negative correlations between heavy metals and phosphatase activity in the soils at the beginning of the incubation. This negative correlation was probably due to the decrease in the enzyme activity in soils treated with PS in which high levels of available P were also found. It is difficult, therefore, to attribute an inhibition of the enzyme activity to the presence of these heavy metals because a high available P concentration in soils also depresses phosphatase activity.     

Sorption and desorption of cobalt by soils and soil components

The sorption of Co by individual soil components was studied at solution Co concentrations that were within the range found in natural soil solutions. Soil-derived oxide materials sorbed by far the greatest amounts of Co although substantial amounts were also sorbed by organic materials (humic and fulvic acids). Clay minerals and non-pedogenic iron and manganese oxides sorbed relatively little Co. It is considered that clay minerals are unlikely to have a significant influence on the sorption of Co by whole soils. Cobalt sorbed by soil oxide material was not readily desorbed back into solution and, in addition, rapidly became non-isotopically exchangeable with solution Co. In contrast, Co was relatively easily desorbed from humic acid and a large proportion of the Co sorbed by humic acid remained isotopically exchangeable. Cobalt sorbed by montmorillonite was more easily desorbed than that sorbed by soil oxide but less easily than that sorbed by humic acid. Cobalt sorption isotherms for whole soils at low site coverage were essentially linear and the gradients of isotherms increased with pH. A comparison of isotherm gradients for whole soils and individual soil components supported the suggestion that Co sorption in whole soils is largely controlled by soil oxide materials.     

Labile ester sulphate in organic matter extracted from podzolic soils

Summary 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 g 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 g 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.     

Sulfur K-edge XANES spectroscopy reveals differences in sulfur speciation of bulk soils, humic acid, fulvic acid, and particle size separates

X-ray absorption near edge structure (XANES) spectra at the sulfur (S) K-edge (E=2472 eV) were compared for bulk soil material, humic and fulvic acid fractions, and different particle size separates from Ah horizons of two arable Luvisols, from an O and a Bs horizon of a Podzol under Norway spruce forest, and from an H horizon of a Histosol (peat bog). In the bulk soil samples, the contribution of reduced organic S (organic mono- and disulfides) to total sulfur increased from 27% to 52%, and the contribution of ester sulfate and SO₄²⁻-S decreased from 39% to 14% of total S in the following order: arable Luvisols Ah—forested Podzol O—Histosol H. This sequence reflects the increasing organic carbon content and the decreasing O₂ availability in that order. Neither sulfonate nor inorganic sulfide was detected in any of the bulk soil samples. For all samples except the Podzol Bs, the XANES spectra of the bulk soils differed considerably from the spectra of the humic and acid fractions of the respective soils, with the latter containing less reduced S (16-44% of total S) and more oxidized S (sulfone S: 19-35%; ester sulfate S: 14-38% of total S). Also the S speciation of most particle size fractions extracted from the Ah horizon of the Viehhausen Luvisol and the Bs horizon of the Podzol was different from that of the bulk soil. For both soils, the contribution of oxidized S species to total S increased and the contribution of sulfoxides and organic mono- and disulfides decreased with decreasing particle size. Thus, sulfur K-edge XANES spectra of alkaline soil extracts, including humic and fulvic acids or of particle size separates are not representative for the S speciation of the original soil sample they are derived from. The differences can be attributed to (i) artificial changes of the sulfur speciation during alkaline extraction (conversion of reduced S into oxidized S, loss of SO₄²⁻ during purification of the extracts by dialysis) or particle size separation (carry-over of water-soluble S, such as SO₄²⁻), but also to (ii) preferential enrichment of oxidized S in hydrophilic water-soluble soil organic matter (ester sulfate) and in the clay fraction of soils (ester sulfate, adsorbed SO₄²⁻).     

Orthophosphate and organic phosphate in the soil solution of four sandy soils in relation to pH‐evidence for humic‐FE‐(AL‐) phosphate complexes

Abstract

Soil from the Ap‐horizon of four acid sandy soils differing mainly in Corg content was adjusted to pH values between 3 and 7.5 with NaOH and HCl respectively and incubated for two weeks. Afterwards, displaced soil solution was obtained and analyzed.

The concentrations of Fe, Al, and P showed a broad minimum in the pH range from 4 to 6. The concentration of these elements strongly increased with the increase of pH to 7.5. Acidification below pH values of 4 led to a slight increase.

Separation of dissolved organic carbon by ultrafiltration before the photometric orthophosphate determination decreased measured concentrations in comparison to direct determination in two of the four soils. This decrease was more pronounced for soil solutions with higher concentrations of organic carbon. The effect of acid hydrolysis of organic phosphorus during orthophosphate determination can be explained by existence of humic‐Fe‐(Al phosphate complexes in the soil solution. These complexes can account for more than 50% of the total organic P in solution.     

Decomposition of 14C-labeled lignins,model humic acid polymers,and fungal melanins in allophanic soils

During 1 yr, CO₂-C losses from 7 agricultural soils containing 0.5–1.5% organic C ranged from 70 to 243 mg 100 g ^{? 1} while losses from three allophanic soils containing 4.9–8.9% organic C varied from 92 to 191 mg. Losses as ¹⁴CO₂ from ring-labeled model and cornstalk lignins averaged about 30% from the agricultural soils compared to about 11% for the allophanic soils. Losses of 2-side chain lignin carbons were about the same as for the ring carbons. Carbon losses from 1-side chain and methoxyl C varied from 42 to 59% in the normal soils while losses from the allophanic soils were a third to a half these values. From 6 to 9% of protein, cysteine, lysine, and glucosamine carbons linked into model humic acid polymers were lost during 1 yr in the allophanic soils compared with 13–24% from the normal soils. Comparable losses from two fungal melanins were 7–15% for the normal soils and 2–4% for the allophanic soils.     

THE NATURE OF ALKALI-SOLUBLE SOIL ORGANIC PHOSPHATES

Fractionation of the phosphates in a sodium hydroxide extract of an arable soil has shown the presence of a number of esters of a type not previously detected in soils. These included several mono-phosphorylated carboxylic acids with C to P ratios of approximately 7 or 8 to I and two esters each containing glycerol, myoinositol, chiroinositol and an unidentified component. Another ester, probably containing two phosphate groups, was also detected but was not completely separated from other compounds containing no P. These esters constituted only approximately 3 per cent of the total soil organic P but considerable losses of organic P occurred during the extraction and isolation procedures. The amounts of the inositol phosphates, nucleoside phosphates, and inorganic pyrophosphate in the extract were also measured.     

Influence of four levels of pyrophosphatase activity on the rate of pyrophosphate hydrolysis in organic soils

Abstract

In this study, the rate of pyrophosphate hydrolysis was measured in four organic soil materials similar in pyrophosphate retention values and in all other respects except pyrophosphatase activity. These soil materials had a bulk density of 0.20 kg/L and a pH (0.01 M CaCl₂) of 5.1, and contained 16% ash and 103 mg P/kg as Mehlich No. 1 extractable P. The difference in pyrophosphatase activity between the soil materials was attributed to response to Cu of previous crops at low values of 1 N HCl‐extractable Cu (10 vs 76 mg Cu/kg) and to pyrophosphatase inhibition by Cu at high Cu values (201 and 479 mg Cu/kg). Pyrophosphatase activity increased from 35.6 to 38.3 mmol/kg/(2h) with Cu contents increasing from 10 to 76 mg/kg, and decreased to 31.9 and 28.3 mmol/kg/ (2h) with Cu contents increasing respectively to 201 and to 479 mg/kg. However, no significant difference in course of pyrophos‐phate hydrolysis was observed among the soil materials under both laboratory and field conditions. The half‐life of pyrophosphate was nearly 1 day under laboratory conditions. The decrease in substrate concentration over time and the corresponding increase in products competing with substrate on active sites of enzymes tended presumably to mask the difference shown in pyrophosphatase activity among organic soil materials. Thus, a difference in pyrophosphatase activities larger than the one considered in this study would be required to influence the rate of pyrophosphate hydrolysis in organic soils of similar pyrophosphate retention characteristics. Such a difference in activity levels was not obtained despite a large difference in Cu contents among the soil materials. It was thus apparent that Cu contents, exceeding that generally found in Quebec organic soils, would not reduce the rate of orthophosphate production from polyphosphate fertilizers containing large amounts of pyrophosphate. Pyrophosphate hydrolysis would be rapid and not affected by a small reduction in pyrophosphatase activity.     

三种黑土中有机碳、氮、磷的形态分布与肥力的关系

土壤腐殖质是土壤的重要组分。土壤的许多属性都直接或间接地与腐殖质的性质有关。我们曾指出^[2]黑土的腐殖物质及其组分与土壤的物理、化学及生物化学有显著的相关性,这表明它们对氮、磷等营养物质的转化、供应及贮存起着重要的作用。     

Influence of intimate association with humic polymers on biodegradation of [C]labeled organic substrates in soil

A variety of [¹⁴C]labeled organic compounds and microbial products were incubated in soil alone or intimately associated with humic acid-type polymers achieved by freeze-drying mixed solutions of the polymers and [¹⁴C]labeled compounds at pH 6. The association of Chlorella protein with the polymers reduced mineralization over 12 weeks by 41%. Similarly decomposition of cysteine and Anabaena flos-aqua cytoplasm was reduced by 26% and glycine 16%. Tyrosine, lysine, aspartic acid, serine, cytosine, glucose, ferulic acid. also polysaccharides of Leuconostoc dextranicus, Azotobacter indicus, Hansenula holstii and Anabaena flos-aqua, as well as cells and cell walls of A. flos-aqua decomposed just or almost as readily when intimately associated with humic polymers as when added alone to the soils. The association with humic polymers did not influence the distribution of residual activity in humic acid, fulvic acid and extracted soil following incubation.     

Effect of ph on precipitation of humic acid from peat and mineral soils on the distribution of phosphorus forms in humic and fulvic acid fractions

Abstract

Humic and fulvic acid fractions were isolated from a mineral soil and a peat by adjusting the pH of the alkali extracts to a range of values from 0.2 to 2.5. Total inorganic and organic forms of phosphorus (P) in the acids were measured by chemical analysis and by ³¹P NMR spectroscopy. As the pH of precipitation of the mineral soil humic acid increased, there was an increase in the total P of the humic acid which related to the inorganic P component. In contrast with the peat, the increases observed in the pH range 0.2 to 1.5 were the result of changes in organic P. Using ³¹P nuclear magnetic resonance spectroscopy, the ratio of inorganic to organic P as mono‐ and di‐esters in the peat humic acid was found to increase from 1:4.8 at pH 2 to 1:19 at pH 2.5. In contrast with mineral soil humic acid, the ratio decreased from 1:6.1 at pH 0.2 to 1:1.3 at pH 2.5. The mono‐ester to di‐ester ratio was about 3 in the peat and 10 in the mineral soil and varied little with pH of precipitation. Phosphonates were detected only in the peat humic acid precipitated in the pH range 1.0 to 2.0     

Irrigation with plant extracts in ecofarming increases biomass production and mineral and organic nitrogen content of plants

Seedlings of alfalfa, rape, spinach, and wheat, potted on sandy soil, were irrigated with an aqueous extract of pea shoot (PE, 9.84 g dry weight l^–1) or a solution of Ca, K, Mg, P, and NO₃‐N salts (SS) in a concentration similar to that in PE, for 31–48 days. In comparison to water‐irrigated controls, both SS and PE treated plants showed nearly equal increases in shoot dry weight (29–40 %), whereas PE‐treated plants had higher fresh weights (38–84 %) due to increased succulence. Treatment with SS did not enhance, but sometimes even reduce, the concentrations of Ca, K, Mg, and several trace elements in shoot tissues. In contrast, PE‐treated plants had higher Ca, K, Mg, and organic N, but lower As and Ni contents and were thus of higher nutritive value. Reduced contents of metals in plant tissue correlated with their reduced solubility in the soil solution, which was not due to changes in pH. Fertilizer components such as K and Mg (metals of lower exchange intensity) were incorporated into the soil to release Ca, Sr, and Ba (metals of higher exchange intensity) and reduce the solubility of most trace elements and metal‐complexing humic substances. In addition, application of Ca precipitated heavy metals and humic complexes directly from the soil solution. This effect was partially overcome by PE. Its carboxylic acids could act as phytochelators of metal ions and as mobilizers of the highly diffusible humic substances which carry metals to roots. It is concluded that continuous PE application replaces the quantities of Ca, K, Mg, P, and organic N, but not of NO₃‐N consumed during plant growth. Using PE does not add any relevant quantities of toxic metals to the plant‐soil system.     

覆膜对有机物料的腐解及土壤有机质特性的影响

砂滤管长期培养试验结果表明,有机物料和农肥施入土壤后,腐解残留率(Yt)与有机物料施入后的时间(t)遵循Yt=Y^λ.t_oe方程式,式中Yo为有机物料缓分解成分的碳理占加入总碳量的百分数,λ为缓解成分的分解速率。覆膜使Yt和Yo值明显降低。田间试验结果表明,覆膜降低了有机质的活性,使PQ值(胡敏酸占可提取腐殖酸的百分数)和A2/A3比值(胡敏酸在波长200nm和300nm处吸光度之比)增高,胡敏酸对光吸收增强。     

Reaction rates of phenolic humus constituents and anilines during cross-coupling

Oxidative coupling processes operative in soil during the formation of stable humic materials and bound residues involving anilines and soil organic matter were studied. We examined the relationship between chemical structure and reactivity for the peroxidase-mediated coupling of potential phenolic humus constituents of plant and microbial origin. The results demonstrated that the acrylic group significantly increased the reactivity of the naturally-occurring phenolic compounds tested. These results suggested that lignin-derived phenols containing the acrylic group, e.g. ferulic acid, may be utilized preferentially during the peroxidase-mediated synthesis of humic materials in soils. We also investigated the peroxidase-mediated cross-coupling of mono-substituted anilines with various phenolic compounds. Reactivity of aniline, nitroaniline and chloroaniline was greatly enhanced in the presence of a highly-reactive electron donor such as ferulic acid. The enhanced reactivity suggested that the aniline compounds were reacting by a different mechanism than when they are present as sole electron donors. The most plausible mechanism is a secondary chemical reaction between anilines and intermediates or products produced during the enzymatic oxidation of phenolic electron donors.     

Nitrogen forms in 1- to 7-year-old opencast lignite mine soils

We studied the distribution of different forms of N in very young (0- to 7-year-old) soils from the Meirama lignite mine in northwest Spain. Total N increased rapidly with soil age, largely in the humic acid-associated fraction. Acid hydrolysis indicated that amino acid N and a hydrolysable unknown form of N increased with soil age. The fractionation reported by Bettany et al. (1980) indicated that alkali/pyrophosphate-extractable humus increased with soil age. All these data suggest that there is rapid stabilization of organic N during the first few years of evolution of these mine soils, to the extent that distribution of N forms in the 7-year-old soil is very similar to that in native soils.     

The involvement of iron and aluminum in the bonding of phosphorus to soil humic acid

Abstract

With a peat soil similar amounts of phosphorus (P) were coprecipitated with humic acid from alkali extracts over a limited range of strongly acidic pH, whereas with a mineral soil the amount was pH dependent. The difference between the two soils relates to the much greater total amounts of inorganic P and aluminum (Al) present in the extract of the mineral soil. In this acid mineral soil, Al rather than iron (Fe) may be involved in the formation of metal bridges in humic acid‐metal‐inorganic P complexes. Neither Al or Fe were implicated in binding of organic P to humic acid. The P species observed in humic acids was dependent on the pH at which they were precipitated from the alkali extracts. In the peat soil the inorganic P was an order of magnitude lower than the organic P.     

Further investigations on the chemistry of fungal “humic acids”

In view of the considerable interest in laboratory-prepared fungal “humic acids” as possible precursors or incorporated structural components of soil humic substances, we degraded four fungal “humic acids” by the relatively mild alkaline cupric oxide oxidation. The oxidation products were extracted into organic solvents, methylated, separated by thin-layer chromatography and identified on a gas chromatographic-mass spectrometric-computer system.Average yields of major degradation products were: (a) aliphatic compounds, 38 per cent; (b) benzene-carboxylic compounds, 25 per cent; and (c) phenolic compounds, 21 per cent. The remaining 16 per cent consisted of a number of dialkyl phthalates. Our data agree with those that we reported earlier when we degraded a number of fungal “humic acids” by the more drastic alkaline permanganate oxidation and show that fungal “humic acids” are enormously complex organic materials containing aliphatic and aromatic structures, (some of which contain N), but only a relatively small proportion of which is phenolic. Most of the aliphatics isolated consisted of alkanes and fatty acids, which are known to persist in soils over long periods of time and are frequently firmly retained by soil humic substances.