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1.
Dissolved organic matter (DOM) plays a fundamental role for many soil processes. For instance, production, transport, and retention of DOM control properties and long-term storage of organic matter in mineral soils. Production of water-soluble compounds during the decomposition of plant litter is a major process providing DOM in soils. Herein, we examine processes causing the commonly observed increase in contribution of aromatic compounds to WSOM during litter decomposition, and unravel the relationship between lignin degradation and the production of aromatic WSOM. We analysed amounts and composition of water-soluble organic matter (WSOM) produced during 27 months of decomposition of leaves and needles (ash, beech, maple, spruce, pine). The contribution of aromatic compounds to WSOM, as indicated by the specific UV absorbance of WSOM, remained constant or increased during decomposition. However, the contribution of lignin-derived compounds to the total phenolic products of 13C-labelled tetramethylammonium hydroxide (13C-TMAH) thermochemolysis increased strongly (by >114%) within 27 months of decomposition. Simultaneous changes in contents of lignin phenols in solid litter residues (cupric oxide method as well as 13C-TMAH thermochemolysis) were comparably small (−39% to +21% within 27 months). This suggests that the increasing contribution of lignin-derived compounds to WSOM during decomposition does not reflect compositional changes of solid litter residues, but rather the course of decomposition processes. In the light of recently published findings, these processes include: (i) progressive oxidative alteration of lignin that results in increasing solubility of lignin, (ii) preferential degradation of soluble, non-lignin compounds that limits their contribution to WSOM during later phases of decomposition.  相似文献   

2.
Dissolved organic matter (DOM) in soils is partially adsorbed when passing through a soil profile. In most adsorption studies, water soluble organic matter extracted by water or dilute salt solutions is used instead of real DOM gained in situ by lysimeters or ceramic suction cups. We investigated the adsorption of DOM gained in situ from three compartments (forest floor leachate and soil solution from 20 cm (Bg horizon) and 60 cm depth (2Bg horizon)) on the corresponding clay and fine silt fractions (< 6.3 μm, separated together from the bulk soil) of the horizons Ah, Bg, and 2Bg of a forested Stagnic Gleysol by batch experiments. An aliquot of each clay and fine silt fraction was treated with H2O2 to destroy soil organic matter. Before and after the experiments, the solutions were characterized by ultra‐violet and fluorescence spectroscopy and analyzed for sulfate, chloride, nitrate, and fluoride. The highest affinity for DOM was found for the Ah samples, and the affinity decreased in the sequence Ah > Bg > 2Bg. Dissolved organic matter in the 2Bg horizon can be regarded as slightly reactive, because adsorption was low. Desorption of DOM from the subsoil samples was reflected more realistically with a non‐linear regression approach than with initial mass isotherms. The results show that the extent of DOM adsorption especially in subsoils is controlled by the composition and by the origin of the DOM used as adsorptive rather than by the mineralogical composition of the soil or by contents of soil organic matter. We recommend to use DOM gained in situ when investigating the fate of DOM in subsoils.  相似文献   

3.
Accurate estimation of the available potassium (K+) supplied by calcareous soils in arid and semi‐arid regions is becoming more important. Exchangeable K+, determined by ammonium acetate (NH4OAc), might not be the best predictor of the soil K+ available to crops in soils containing micaceous minerals. The effectiveness of different extraction methods for the prediction of K‐supplying capacities and quantity–intensity relationships was studied in 10 calcareous soils in western Iran. Total K+ uptake by wheat grown in the greenhouse was used to measure plant‐available soil K+. The following methods extracted increasingly higher average amounts of soil K+: 0.025 M H2SO4 (45 mg K+ kg?1), 1 M NaCl (92 mg K+ kg?1), 0.01 M CaCl2 (104 mg K+ kg?1), 0.1 M BaCl2 (126 mg K+ kg?1), and 1 M NH4OAc (312 mg K+ kg?1). Potassium extracted by 0.01 M CaCl2, 1 M NaCl, 0.1 M BaCl2, and 0.025 M H2SO4 showed higher correlation with K+ uptake by the crop (P < 0.01) than did NH4OAc (P < 0.05), which is used to extract K+ in the soils of the studied area. There were significant correlations among exchangeable K+ adsorbed on the planar surfaces of soils (labile K+) and K+ plant uptake and K+ extracted by all extractants. It would appear that both 0.01 M CaCl2 and 1 M NaCl extractants and labile K+ may provide the most useful prediction of K+ uptake by plants in these calcareous soils containing micaceous minerals.  相似文献   

4.
不同浸提剂处理森林土壤溶解性有机碳含量比较   总被引：1，自引：0，他引：1  
丁咸庆  柏菁  项文化  侯红波  彭佩钦 《土壤》2020,52(3):518-524
为了解亚热带森林土壤溶解性有机碳(DOC)的特征规律,采用培养离心的方法获取土壤溶液测得DOC含量,对比传统水溶性有机碳(WSOC)提取法间的差异。选取湖南大山冲森林公园保存完好的3种亚热带典型次生林地,按10cm一层采集剖面土壤,采用不同方法提取测定土壤DOC和WSOC含量,分析与土壤理化指标的相关性及方法间的显著性关系。结果表明:①典型森林土壤DOC或WSOC含量随土壤剖面深度的增加,呈显著下降趋势。培养离心提取测得的土壤DOC含量明显较低,仅0.82～9.52 mg/kg,超纯水浸提的风干土WSOC含量达10.56～249.19 mg/kg,而0.5 mol/L K_2SO_4提取的鲜土WSOC含量达155.70～576.94 mg/kg,0.5mol/L K_2SO_4浸提的干土WSOC含量最高,达158.94～797.56 mg/kg,含量表现为:DOC干土超纯水浸提WSOC鲜土K_2SO_4浸提WSOC干土K_2SO_4浸提WSOC;②3种次生林土壤DOC或WSOC含量存在显著差异,不同方法测定的含量均表现为针叶林常绿阔叶林落叶林;③培养离心法测得土壤DOC含量与其他测定方法间存在极显著正相关(P0.01),并且土壤DOC和WSOC均与土壤pH、总有机碳、胡敏酸、富啡酸、全氮、全磷、速效态氮以及微生物生物量碳氮达到极显著相关(P0.01),与土壤含水率和容重显著相关(P0.05)。培养离心法测得土壤DOC含量远低于水溶液提取WSOC含量,该方法下的测得值更接近于原位土壤溶解性有机碳实际值。  相似文献   

5.
Abstract

It was the objective of this study to compare the suitability of different extractants for predicting the availability of sulfur (S) in natural grassland in a sulfur response trial on three different soil types in the Inner Mongolia steppe of China. For soil analysis, seven different extractants have been employed. The inorganic SO4–S concentration was determined by ion chromatography. Additionally, in the Ca(H2PO4)2 extract the total soluble S was determined employing turbidimetry. Weak salt solutions (0.15% CaCl2, Ca(H2PO4)2, and KH2PO4) extracted similar amounts of SO4–S. Extraction with 0.025 M KCl provided the lowest SO4–S values. Deionized water dissolved significantly more SO4–S in the control plots than most weak salt extractants. The concentration of soluble organic S decreased in the control plots after 100 days of plant growth, indicating that the organic S pool contributed significantly to the S nutrition of the forage crops. Significant relationships among the SO4–S in the soil determined in different extracts and crop yield, sulfur content in the forage, and total sulfur uptake were only found for the Ca(H2PO4)2 extract. In general, the correlation coefficients proved to be unsatisfactory for field experimentation.  相似文献   

6.
Dissolved organic matter (DOM) is an important part of the microbially utilizable organic matter in soils. This paper describes an incubation experiment by which the lability and mobility of DOM extracted from forest‐floor materials are related to their age and degree of degradation. DOM extracted from a chronosequence of decomposing leaves (green leaves, fresh fallen leaves, litter [1 y weathering], fibric matter [2–3 y], hemic matter [>3 y], or peat [100+ y]) was applied to intact soil cores, and the CO2 produced over 5 d was measured to determine biodegradability. Biodegradability of DOM varied somewhat along the chronosequence, with the green leaves yielding more CO2 on an equal C basis than the older substrates and equivalent to glucose which was used as a reference substrate. Thus, the DOM extracts of the older substrates contain some refractory components. The humic‐acid content (or that of its precursors) of the extracts from older substrates relates to the lowered lability. The hydrophobic and hydrophilic content of DOM extracted from substrates was not related to CO2 production in the incubation studies conducted.  相似文献   

7.
Abstract

Open and closed incubation systems were studied as means of quantifying sulfate fractions in sphagnum peat moss. Sulfate was extracted in the closed system with a 0.15% CaCl2‐H2O or a 500 mg P/L extractant. Sulfate was extracted in the open system with 10 mM KC1, 0.15% , CaCl2‐H2O, or 500 mg P/L extractant. Extractants were quantified by ion chromatography. Phosphate extractant released more sulfate than CaCl2, in the closed system. There was a significant increase over time of sulfate released by the CaCl2 extractant. In the open system, there was no significant difference in release and total amounts leached of sulfate‐S between extractants. The closed system released more sulfate‐S than the open system. Phosphate extractants in both systems mineralized 43% of initial sulfur content  相似文献   

8.
Carbohydrates are an important component of soil organic matter, and a method is needed to quantify them, which would be efficient in terms of time and cost. Different extractants and methods were examined in this work for their efficiency to extract carbohydrate C from four calcareous soils. Four extractants (distilled water, 0.5 M potassium sulfate (K2SO4), and 0.25 and 0.5 M sulfuric acid (H2SO4)) and three incubation methods (shaking for 16 h, heating in an oven (85 °C) for 16 h, and heating in a water bath (85 °C) for 2.5 h) were compared. The results show that significantly more carbohydrate C was extracted from all four soils with oven and water bath heating of the soil–extractant suspensions than with shaking them at room temperature. The efficiency of the extractants decreased in this order: 0.5 M H2SO4 > 0.25 M H2SO4 > 0.5 M K2SO4. The combination of the heated–water bath incubation method with 0.5 M H2SO4 as extractant was the most efficient method.  相似文献   

9.
Abstract

A laboratory incubation experiment was conducted to study the influence of organic matter and lime application on the recovery of added boron (B) by four different extractants (hot‐CaCl2, mannitol‐CaCl2, tartaric acid, and ammonium acetate) in two B‐deficient acid alluvial soils. Soils were brought to four relatively constant pHs and three organic matter levels before application of B. Recovery percentages of 23.9 to 60.9 of added B by the four extractants indicate a soil fixation of B. This is more so in fine‐than in coarse‐textured soils. Both liming (from pH 4.8 to 6.8) below neutrality and organic matter application increased such recovery of added B in all the extractable forms, the effect being more pronounced in fine‐than in coarse‐textured soils. A positive interaction between liming and organic matter particularly at the latter's higher level was observed. Complexation of added B and coating of the surfaces of Fe‐and Al‐oxides by soluble organic compounds are suggested as the possible reasons for such increased recovery of added B in soils.  相似文献   

10.
Abstract

Relative suitability of different extraction procedures for estimating available zinc (Zn) and copper (Cu) in soils was assessed using DTPA, 0.1 N HCl, ammonium acetate+EDTA, and double acid (HCl+ H2SO4) as extractants and rice as a test crop in Neubauer experiment. The relationships between Zn concentration and uptake of Zn by rice plants and Zn extracted by the different methods showed that DTPA‐TEA, pH 7.3, could very suitably be used to assess Zn availability in soils. However, 0.1 N HCl was better for assessing the Cu availability in soils to the rice plants. Water‐soluble and exchangeable fractions of Zn and Cu had significant positive correlations with Zn and Cu concentrations, respectively obtained by all the four extractants tested. The results also showed that DTPA and ammonium acetate+EDTA extracted organically bound Zn, whereas DTPA, 0.1 N HCl and ammonium acetate+EDTA extracted organically bound Cu. Water‐soluble, exchangeable and organic matter bound fractions exhibited significant relationships with Zn and Cu concentrations, their uptake and rice dry matter yield.  相似文献   

11.
The more labile forms of aluminium in a range of soils from areas of permanent grassland were determined with a number of selective extractants. The amounts of exchangeable A1 extracted with molar KCl were dependent upon pH, while the amounts exchangeable with 0.3 M LaCl3, although much greater, were not well correlated with pH. There were good correlations between soil organic C content and A1 extracted by (i) 0.5 M EDTA and (ii) 0.1 M potassium pyrophosphate. Pyrophosphate extracted greater amounts than any of the other extractants (sodium citrate/dithionite, ammonium oxalate (dark), acid oxalate (UV radiation), as well as those already mentioned). It was concluded that much of the extractable A1 in soils was associated with organic matter. Addition of lime to one of the soils reduced the amount of A1 extracted by all reagents except dithionite and acid oxalate solutions. There were considerable differences between soils in their release of A1 to continuous leaching with 0.01 M CaCl2. Despite these differences between the soils in organically bound extractable Al, the differences in the amounts and patterns of release of A1 with CaCl2 did not appear to be related to organic matter contents, nor to the other determined properties.  相似文献   

12.
The retention of dissolved organic matter in soils is mainly attributed to interactions with the clay fraction. Yet, it is unclear to which extent certain clay‐sized soil constituents contribute to the sorption of dissolved organic matter. In order to identify the mineral constituents controlling the sorption of dissolved organic matter, we carried out experiments on bulk samples and differently pretreated clay‐size separates (untreated, organic matter oxidation with H2O2, and organic matter oxidation with H2O2 + extraction of Al and Fe oxides) from subsoil horizons of four Inceptisols and one Alfisol. The untreated clay separates of the subsoils sorbed 85 to 95% of the dissolved organic matter the whole soil sorbed. The sorption of the clay fraction increased when indigenous organic matter was oxidized by H2O2. Subsequent extraction of Al and Fe oxides/hydroxides caused a sharp decrease of the sorption of dissolved organic matter. This indicated that these oxides/hydroxides in the clay fraction were the main sorbents of dissolved organic matter of the investigated soils. Moreover, the coverage of these sorbents with organic matter reduced the amount of binding sites available for further sorption. The non‐expandable layer silicates, which dominated the investigated clay fractions, exhibited a weak sorption of dissolved organic matter. Whole soils and untreated clay fractions favored the sorption of ”︁hydrophobic” dissolved organic matter. The removal of oxides/hydroxides reduced the sorption of the lignin‐derived ”︁hydrophobic” dissolved organic matter onto the remaining layer silicates stronger than that of ”︁hydrophilic” dissolved organic matter.  相似文献   

13.
Abstract

Soils have substantial capacity for sorption of sulfur dioxide (SO2) but little is known about the nature of the sorbed S. Three surface soils varying in pH, organic matter, CaCO3 equivalent and surface area were exposed to air containing 5% SO2 and subsequently analyzed by ten different procedures to characterize the sorbed S. Most of the sulfur retained by soils after exposure to SO2 could be recovered as CaCl2‐extractable S, Ca(H2PO4)2‐extractable S, or S released as H2S by hydriodic acid (HI). Only small amounts of sulfur could be recovered as tetrachloromercurate (TCM)‐extractable S, S released as SO2 by HCl, or S released as H2S by HCl + Zn, HCl + Sn, or Raney Ni and NaOH. However, large amounts of S released as SO2 by HCl were recovered from the air‐dry Webster and the moist Storden soils indicating that SO2 sorption is influenced by organic matter in air‐dry soils and by CaCO3 in moist soils.  相似文献   

14.
Labile ester sulphate in organic matter extracted from podzolic soils   总被引：1，自引：0，他引：1  
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.  相似文献   

15.
The dissolution of organic matter in soil is of fundamental relevance for the fate of organic contaminants associated with organic matter and for the microbial availability of organic matter. In this study, the kinetics of soil organic matter (SOM) dissolution from a sandy forest soil was investigated under different electrolyte conditions, using a continuous extraction method. The mathematical analysis of the concentration signal obtained from extractions with constant flow rates and after sudden flow rate changes showed that the dissolution of SOM is diffusion limited. The dissolution rate was lower during extraction with 0.01 M CaCl2. The reaction on sudden flow rate changes was slower when extracting with 0.01 M CaCl2 as compared to water, and the mechanism was different. These observations were explained by a gel phase developing in the swelling SOM. The lower dissolution rates found for extractions with 0.01 M CaCl2 could indicate a more stable gel structure in the presence Ca2+. The development of the gel phase may be influenced by mechanical strain due to increased flow rates.  相似文献   

16.
Abstract

Mustard (Brassica juncea) is an important oilseed crop of northern India, which is widely grown in Delhi and adjoining States. This crop has a relatively high requirement of sulphur (S), and is sensitive to S‐deficiency. For predicting response of mustard to S application, several extractants have been tried with variable results. Since selection of a promising extractant for a particular soil needs careful consideration, the present investigation was planned to select the most promising extractant to predict the availability of S to mustard grown on Inceptisols of Delhi. For this purpose, a greenhouse experiment was conducted with twenty soils (two from each often important soil series from the cultivated alluvial soil belt of Delhi. Nine extractants, commonly used for estimating the availability of S, were evaluated and S in soil extract and in plant digest was estimated using the turbiditimetric method. The results indicate that the phosphate salt methods extracted comparatively more S than other extractants. The amount of S extracted by these extractants was found in the following order: KH2PO4‐500 ppm P>Ca(H2PO4)2‐500 ppm P>0.001 M HCl>NaOAc+HOAc>heat soluble S>0.15% CaCl2>l% NaCl> water soluble S>NH4OAc+HOAc. Simple correlation coefficients of the amounts of S extracted by different extractants and the forms of S with the plant parameters were worked out. To determine the combined effect of soil characteristics on S extraction by different extractants, stepwise multiple regression analysis was carried out. Based on this study, the suitability of the extractants for mustard crops in Inceptisols of Delhi may be arranged as follows: 0.15% CaCl2>water soluble S>0.001 M HCl>Ca(H2PO4)2‐500 ppm>1%NaCl>NH4OAc+HOAc>NaOAc+HOAc>KH2PO4‐500 ppm P>heat soluble S.  相似文献   

17.
The direct effects of dissolved organic matter (DOM) on the sorption of orthophosphate onto gibbsite, goethite, and kaolin were examined using a one-point phosphorus sorption index and the linear Tempkin isotherm model. DOM extracted from fresh and decomposed agricultural residues, as well as model organic and humic acids, were used. Changes in the chemical and sorptive characteristics of the DOM in the absence and presence of added orthophosphate (50 mg l−1) were also determined. For residue-derived materials, DOM sorption to all minerals correlated well with percent hydrophobicity, apparent molecular weight, and phenolic acidity in the absence of added orthophosphate. Sorption of DOM to goethite and gibbsite was significantly decreased in the presence of added P. The correlation coefficient values of percent hydrophobicity, apparent molecular weight, and phenolic acidity to sorption also declined in the presence of added P. Thus, the addition of P substantially lowered fractionation of DOM after sorption to goethite and gibbsite. In contrast, few significant P sorption-induced differences were observed in the kaolin system. According to one-point P sorption results, DOM in the form of Aldrich humic acid, oxalate, and decomposed clover and corn residue, significantly inhibited P sorption to goethite at concentrations of 50 and 200 mg total soluble carbon (CTS l−1). Phosphorus sorption to gibbsite was significantly inhibited by 50 mg CTS l−1 derived from decomposed corn residue, fresh dairy manure residue, and oxalate solution. At 200 mg CTS l−1, all DOM solutions were found to inhibit P sorption to gibbsite. This study suggests that DOM inhibition of P sorption depends on the chemical properties of both the sorbent and the DOM itself. In general, DOM from decomposed organic materials inhibited P sorption to a greater extent than did DOM derived from fresh materials. This stronger inhibition highlights the importance of microbial processes in the release of soluble soil P, a key determinant of P availability to plants.  相似文献   

18.
Determination of the labile soil carbon (C) and nitrogen (N) fractions and measurement of their isotopic signatures (δ13C and δ15N) has been used widely for characterizing soil C and N transformations. However, methodological questions and comparison of results of different authors have not been fully solved. We studied concentrations and δ13C and δ15N of salt‐extractable organic carbon (SEOC), inorganic (N–NH4+ and N–NO3?) and organic nitrogen (SEON) and salt‐extractable microbial C (SEMC) and N (SEMN) in 0.05 and 0.5 m K2SO4 extracts from a range of soils in Russia. Despite differences in acidity, organic matter and N content and C and N availability in the studied soils, we found consistent patterns of effects of K2SO4 concentration on C and N extractability. Organic C and N were extracted 1.6–5.5 times more effectively with 0.5 m K2SO4 than with 0.05 m K2SO4. Extra SEOC extractability with greater K2SO4 concentrations did not depend on soil properties within a wide range of pH and organic matter concentrations, but the effect was more pronounced in the most acidic and organic‐rich mountain Umbrisols. Extractable microbial C was not affected by K2SO4 concentrations, while SEMN was greater when extracted with 0.5 m K2SO4. We demonstrate that the δ13C and δ15N values of extractable non‐microbial and microbial C and N are not affected by K2SO4 concentrations, but use of a small concentration of extract (0.05 m K2SO4) gives more consistent isotopic results than a larger concentration (0.5 m ).  相似文献   

19.
A comparison of different indices for nitrogen mineralization   总被引：3，自引：0，他引：3  
Indices of N mineralization in soils of contrasting texture, pH, and organic matter contents were compared at different dates during the growing season. The indices were derived from a 12-week aerobic incubation, determination of the amount of microbial biomass at the start of the incubation, determination of the increase in NH 4 + after boiling with 2 M KCl for 2h, and extraction of total soluble N with 0.01 M CaCl2. Cumulative mineral N increased linearly with time in the course of the incubations. Rates of mineralization in soil samples taken in March 1989 and 1990 were significantly correlated with soluble organic N, while correlations between the mineralization rate and the increase in NH 4 + after boiling with 2 M KCl for 2 h were poor for sandy soils and absent for loamy soils. Correlations between NH 4 + after boiling with 2 M KCl for 2h and the soil N concentration were highly significant, but no general relationship was found between the mineralization rate and the soil N concentration. Neither biomass N nor biomass C was significantly correlated with the mineralization rate or with one of the chemical indices. Among the methods tested, soluble organic N extracted with 0.01 M CaCl2 was the only method with any promise for routine measurement of the mineralization capacity of the individual sites.  相似文献   

20.
Abstract

Sulfate (SO4 2‐) is present in soils as salts of various metals, and the different metals associated with sulfate may influence adsorption of SO4 2‐by soils. The analytical method used for determination of SO4 2‐could be affected by the type of metal associated with the SO4 2‐. Four analytical methods based on different principles were evaluated for determination of SO4 2‐in different metal salts and in soil extracts obtained with three extractants {0.1M lithium chloride (LiCl), 0.15% calcium chloride (CaCl2), and 500 mg P/L as calcium phosphate [Ca(H2PO4)2]}. The analytical methods were: (i) a methylene blue (MB) colorimetric method after the reduction of SO4 2‐to hyrogen sulfide (H2S), (ii) an ion Chromatographie (IC) method, (iii) a turbidimetric (TD) method, and (iv) an indirect barium (Ba) atomic absorption spectrophotometric (SP) method. The recovery of SO4 2‐associated with various mono‐, di‐, and tri‐valent metals was quantitative by the MB method. But, trivalent metals, such as aluminum (Al), indium (In), lanthanum (La), and scandium (IC), decreased the recovery of SO4 2‐by the other three methods. The MB and IC methods gave similar values for SO4 2‐in soils by using the three extractants. The TD and SP methods gave variable results and, in general, underestimated the amounts of SO4 2‐in soils. Among the four methods, the MB and IC methods were the most accurate and precise.  相似文献   

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