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1.
Equilibrium studies on soil require reliable estimates of ion concentrations in the soil solution under field conditions. We evaluated the previously described iterative method to approximate the equilibrium soil solution (ESS) with four acid forest soils. We examined for which ions the ESS is suitable, making use of the fact that concentrations in water extracts are functions of the soil: solution ratio. The electric conductivity, pH, and the concentrations of base cations, Mn2+, NO?3, SO42+, and dissolved organic carbon (DOC) were usually linear with the soil:solution ratio in water extracts, whereas no relation was observed for Al (with one exception) and Fe. Assuming that the ESS can be attributed the soil solution ratio of the field moist soil at the time of sampling, concentrations appeared as the continuation of the linear relation with the soil: solution ratio for base cations, pH, and the electric conductivity. This indicates that the ESS actually represents field conditions for these solution properties. For Al water extracts allowed no evaluation of the ESS result. The ESS underestimated SO42? concentrations under field conditions, presumably because the lack of DOC in the solutions added distorts the balance amongst anions.  相似文献   

2.
Chemical data for stagnopodzol soils and soil solutions are presented for grassland and plantation coniferous forest systems in upland mid-Wales. The results show that the introduction of the forest, with consequent increase in anion concentrations, has increased concentrations of Al in the soil solution by 1.5 to 3 times. Hydrogen ion concentrations have only increased by a small amount. Simple cation exchange relationships have been proposed to explain some of these changes.  相似文献   

3.
Abstract

Despite the increasing prevalence of salinity worldwide, the measurement of exchangeable cation concentrations in saline soils remains problematic. Two soil types (Mollisol and Vertisol) were equilibrated with a range of sodium adsorption ratio (SAR) solutions at various ionic strengths. The concentrations of exchangeable cations were then determined using several different types of methods, and the measured exchangeable cation concentrations were compared to reference values. At low ionic strength (low salinity), the concentration of exchangeable cations can be accurately estimated from the total soil extractable cations. In saline soils, however, the presence of soluble salts in the soil solution precludes the use of this method. Leaching of the soil with a prewash solution (such as alcohol) was found to effectively remove the soluble salts from the soil, thus allowing the accurate measurement of the effective cation exchange capacity (ECEC). However, the dilution associated with this prewashing increased the exchangeable calcium (Ca) concentrations while simultaneously decreasing exchangeable sodium (Na). In contrast, when calculated as the difference between the total extractable cations and the soil solution cations, good correlations were found between the calculated exchangeable cation concentrations and the reference values for both Na (Mollisol: y=0.873x and Vertisol: y=0.960x) and Ca (Mollisol: y=0.901x and Vertisol: y=1.05x). Therefore, for soils with a soil solution ionic strength greater than 50 mM (electrical conductivity of 4 dS/m) (in which exchangeable cation concentrations are overestimated by the assumption they can be estimated as the total extractable cations), concentrations can be calculated as the difference between total extractable cations and soluble cations.  相似文献   

4.
Abstract

Mixed‐bed cation + anion exchange resin bags are frequently used to assess in situ nutrient availability in forest soils, and have demonstrated their utility for comparing the impacts of different disturbances associated with treatments. They are generally installed in organic or mineral soil horizons for a certain time period, then recovered and extracted, to inform about nutrient availability during that period. For the method to be effective, the ion exchange sites of resins must be clear from any contaminants prior to installation in the soil. A washing procedure to be conducted before in situ burial of mixed‐bed resins was developed and is described. The IONAC NM‐60 H+/OH‐ resins are consecutively washed with 2 N NaCl, deionized water, and 0.1 N NaOH. Finally, resins are rinsed with deionized water and stored moist and cold until bag preparation and burial in the soil.  相似文献   

5.
In acid forest soils pores draining under conditions of low water tension contain a solution usually differing in composition from the equilibrium solution of the bulk soil. For tree nutrition, the former was described as comparable to the bulk soil solution or less favourable. Our recent work on solution quality contradicted the universal validity of these findings. It turned out that the methods usually recommended tend to consistently reproduce the pattern of more advanced acidification of coarse pores. We applied our combination of methods to a range of soils to find out whether our previous finding of more favourable solution conditions in undisturbed soil samples as compared to the bulk soil is common or rather an exception. Undisturbed cores and bulk soil were sampled from four forested sites differing in pH and base saturation. We used an iterative procedure to adjust the equilibrium soil solution of disturbed soil and a water extraction with a soil:solution ratio of 1:2. To extract solution from undisturbed soil cores only small volumes of water were added, and we distinguished analytically between total (by ICP) and ionic (by CE) concentrations of cations. We calculated Ca/Al molar ratios and the fraction of (Al3+ + H+) on total cationic charge in solution as criteria for solution quality. Whereas with total concentrations, there always appeared to be less favourable conditions in the soil pore solution, free ionic concentrations allowed a differentiation between the soils. In view of plant nutrition, the quality of the soil solution from undisturbed samples was better, equal to, or worse than that of the bulk soil, suggesting that forest sites represent a continuum with respect to these chemical gradients. Even in soils where gradients are not observed it is not necessary to assume an equilibrium achieved by internal processes to exist between coarse pores and the bulk soil.  相似文献   

6.
Abstract. In most soils of temperate regions nitrate is not held on soil surfaces and moves freely in solution. But when soils carry positive charges, nitrate is held as an exchangeable anion. As a result, leaching of nitrate is delayed relative to the movement of water. The delay can be predicted provided the anion exchange capacity (AEC) can be measured and the concentration of counter-anions is known. For soils with variable charge, the AEC varies with both pH and ionic strength, and the effective AEC should be determined under conditions similar to those in soil solution. A simple leaching method is described which satisfies this requirement. Delays in the leaching of nitrate measured in columns of repacked soil were strongly related to the AEC.  相似文献   

7.
Abstract

Knowledge of the change in soil extractable phosphorus (P) as a consequence of soil P fertilization could be useful in discriminating soils with a potential for soil P release to runoff or movement of P along the soil profile. In this research, soils with low to medium P retention capacity were equilibrated for 90 days with soluble P (KH2PO4) at rate of 100 mg P kg‐1 soil. After this period, soil samples both with and without the P addition were analyzed using six conventional methods: 1) Olsen, 2) Bray 1,3) Mehlich3,4) Egner, 5) Houba, dilute CaCl2 solution, and 6) distilled water, and three “innovative”; P‐sink methodologies: 1) Fe oxide‐coated paper strip, 2) anion exchange resin membrane, and 3) cation‐anion exchange resin membrane. The soils without P addition had low levels of extracted P as determined by all nine procedures. Net increases in the amount of P extracted from the soils with added P ranged from 4.2 mg kg‐1 (CaCl2 extraction) to 57.6 mg kg‐1 (cation‐anion resin membrane extraction). Relationships between change in extracted P and i) physical and chemical characteristics, and ii) soil P sorption properties are also presented and discussed.  相似文献   

8.
Sago palms (Metroxylon sagu Rottb.) growing on peat soils were found to grow more slowly and to show a lower production than palms growing on mineral soils. This difference was related to the physical and chemical constraints of peat soils, which include low bulk density, high acidity, and low N, P, K, Ca, Zn, and Cu levels. In coastal lowland peat soils, the distance from the sea has been found to be an important determinant of soil elemental composition. We predicted that a sufficient supply of N at the rosette stage would improve sago palm growth and that the availability of N in soil to which controlled release N fertilizer was applied might be higher than that in soil treated with soluble fertilizer. To investigate the changes in the nutrient composition of peat soils at various distances from the sea and the effect on sago palm growth, we studied sago palm areas in Indonesia and Malaysia. To observe the influence of N on the growth performance, we also conducted a fertilizer experiment on coastal lowland peat soil in Indonesia. Distance from the sea had no significant effect on the cation concentration in the soil solution (with the exception of Mg) or on the levels of soil-exchangeable cations. No significant differences were observed between the concentrations of exchangeable cations in surface peat soils and those in mature leaves. However, the concentrations of K, Na, and Ca in mature leaves increased significantly with their concentrations in the soil solution. This finding implies that the concentrations of cations in sago palm leaves depend directly on the concentrations of cations in the soil solution. No significant effect of N fertilizers on plant height and leaf formation was observed. N fertilizers applied twice a year did not affect appreciably the foliar concentration of N determined in December 1998 (5 months after the initial application) and December 1999. In June 2000, we detected a significantly higher concentration of N (p < 0.01) in young leaves of the palms treated with LP-100 or urea than in control leaves. However, no significant difference was detected between the LP-100 and urea treatments in the concentration of N in both mature and young leaves. This finding indicated that the concentration of N in sago palm leaves increased with the level of soil-applied N, regardless of whether N was applied as controlled release fertilizer or in the soluble form. We anticipate that a significant difference in the effects of these N fertilizers may occur during the next rainy season, when there should be a considerable loss of soluble N.  相似文献   

9.
Iodine-129 is an important radionuclide released from nuclear facilities because of its long radioactive half-life and its environmental mobility. Its retention in surface soils has been linked to pH, organic matter, and Fe and Al oxides. Its inorganic solution chemistry indicates I will most likely exist as an anion. Three investigations were carried out to provide information on the role of the inorganic and organic chemistry during sorption of I by soil. Anion competition using Cl? showed that anion exchange plays a role in I sorption in both mineral and organic soils. The presence of Cl decreased the loss of I? from solution by 30 and 50% for an organic and a carbonated sandy soil respectively. The I remaining in solution was associated primarily with dissolved organic carbon (DOC). The loss rate from solution appears to depend on two reactions of I with the soil solids (both mineral and organic) creating both a release to and a loss from solution, and the reaction of I with the DOC (from very low to high molecular weight). Composition analyses of the pore water and the geochemical modelling indicate that I sorption affects the double-charged anion species in solution the most, particularly SO4 ?. Iodide introduced to natural bog groundwater at three concentrations (10?3, 10?1 and 10 meq L?1) remained as I? and was not lost from solution quickly, indicating that the association of I with DOC is slow and does not depend on the DOC or I concentration. If sorption of I to soil solids or DOC is not sensitive to concentration, then stable I studies, which by necessity must be carried out at high environmental concentrations, can be linearly extrapolated to radioactive I at much lower molar concentrations.  相似文献   

10.
Groundwater pollution by nitrate from agricultural fields is a worldwide problem. To improve the understanding of nitrate transport processes through volcanic ash soils overlying groundwater aquifers, salt sorption experiments were performed. Salt sorption is the process that involves the simultaneous use of cation and anion adsorption mechanisms without changing the pH. Prepared six different concentrations of potassium chloride (KCl) solutions were mixed with soil samples. Anion and cation contents of the liquid and solid phases were determined. Experiments were performed in triplicate of six kinds of KCl solutions for three types of soils. Thus, total 54 of samples were analyzed. Relationships between ionic strength and sorption capacity increments of cations and anions were determined. The results show that if ionic strength of the infiltrating solution to the volcanic ash soil is known, the ECEC (effective cation exchange capacity) and EAEC (effective anion exchange capacity) can be reliably estimated. The resulting prediction equations can be included to improve reactive transport simulation models. Consequently, it will be possible to better understand solute transport with changing sorption capacity for the solid soil phase.  相似文献   

11.
Abstract

The effect of soil pH on the exchangeability and solubility of soil cations (Ca, Mg, Na, K, and NH4‐N) and anions (NO3‐N, Cl, and P) was investigated for 80 soils, spanning a wide range in physical and chemical properties and taxonomic groups. This information is needed from environmental and agronomic standpoints to estimate the effect of changes in soil pH on leachability and plant availability of soil nutrients. Soils were incubated with varying amounts of acid (H2SO4) and base (CaCO3) for up to 30 days. Although acid and base amendments had no consistent effect on cation exchangeability (as determined by neutral NH4OAc), amounts of water‐soluble Ca, Mg, Na, K, NH4‐N, and P decreased, while NO3‐N and Cl increased with an increase in soil pH. The increase in cation solubility was attributed to an increase in the negative charge of the soil surface associated with the base addition. The change in surface electrostatic potential had the opposite effect on amounts of NO3‐N and Cl in solution, with increases in N mineralization with increasing soil pH also contributing to the greater amount of NO3‐N in solution. The decrease in P solubility was attributed to changes in the solubility of Fe‐, A1‐, and Ca‐P complexes. The logarithm of the amount of water‐soluble cation or anion was a linear function of soil pH. The slope of this relationship was closely related (R2 = = 0.90 ‐ 0.96) to clay content, initial soil pH, and size of the cation or anion pool maintaining solution concentration. Although the degree in soil pH buffering increased with length of incubation, no effect of time on the relationship between cation or anion solubility and pH was observed except for NO3‐N, due to N mineralization. A change in soil pH brought about by acid rain, fertilizer, and lime inputs, thus, affects cation and anion solubility. The impact of these changes on cation and anion leachability and plant availability may be assessed using the regression equations developed.  相似文献   

12.
In the quest for better understanding of cation movement through undisturbed soils, leaching experiments on 300-mm long undisturbed soil columns of two contrasting soils were carried out. One soil was a weakly-structured alluvial fine sandy loam, the other a well-structured aeolian silt loam. About 2000 mm of solutions of MgCl2 and Ca(NO3)2 of 0·025 M were applied at unsaturated water flow rates of between 3 and 13 mm h?1. Solute movement was monitored over several weeks by collecting effluent under suction at the base. In the sandy loam anion transport was influenced by exclusion from the double layer, whereas in the Ramiha soil anion adsorption occurred. Cation transport was described by coupling the convection-dispersion equation with cation exchange equations. Good simulations of the Mg2+ and Ca2+ concentrations in the effluent and on the exchange sites were obtained if 80% of the exchangeable cations, as measured using the 1 M ammonium acetate method, were assumed to be active. Local physical or chemical disequilibrium did not need to be explicitly taken into account. About 400 kg ha?1 of native potassium was leached from the alluvial soil, but only about 10 kg ha?1 was leached from the aeolian soil. The convection-dispersion equation coupled with exchange theory was found to describe cation transport under unsaturated flow through undisturbed soil satisfactorily.  相似文献   

13.
Self-diffusion coefficients of calcium, sodium, rubidium and caesium on the topsoils and subsoils of contrasting soil series are presented. The distribution ratios of each cation on each soil, at the moisture content of the diffusion experiments, have been calculated by extrapolation from series of suspensions. Diffusion coefficients were found in each case to be greater than expected by considering the liquid phase alone. Surface-phase impedance factors, fs, were calculated. Although impedance factors are considerably smaller on the surface than in solution, the surface flux may exceed the flux in the liquid phase. Differences of an order of magnitude separated average values of fs for each cation. For a given cation, variations between soils were considerably less. No correlation was found between fs and soil mineralogy or composition. Values of fs were found to decrease with increasing distribution ratio. Reasons for this observation are discussed, in particular the energy of adsorption of the cations. The possibility of extrapolating these findings to other soils, to potassium and to other cations is discussed.  相似文献   

14.
Abstract

The chemical characterization of soil phosphorus (P) desorbed by anion and cation exchange membranes is of major importance to better understand which P forms are available to plants in short‐ and long‐term time periods. Two distinct soils, one acidic and one calcareous, were analyzed for P using two extraction procedures with mixed anion and cation exchange membranes. The short‐term (ST) experiment evaluated the effect of increasing the extraction periods up to 24 h, whereas the long‐term (LT) experiment consisted of a sequential extraction procedure using up to seven successive 24‐h extractions. In both experiments, the Chang and Jackson inorganic P fractionation methodology was carried out after each extraction treatment, and each treatment consisted of three replicates. Data were statistically analyzed by ANOVA and nonlinear regressions. In the ST experiment, increasing the extraction time increased the extracted P according to an asymptotic relationship (y=c?ab x ). Extracted P proceeded from the most labile fractions in the acidic soil. In calcareous soils, calcium phosphates may also contribute for extractable P. The LT experiment revealed that a single extraction, regardless of that extraction method, cannot predict the long‐term capacity of soils to supply P to the plants. An exponential relationship (P=a×n b ) was found between extracted P and the extraction number. Desorbed P proceeded from the most labile fractions in the acidic soil. However, in calcareous soils, some precaution is needed when considering the biological meaning of the results, because the occluded Fe phosphates also revealed significant decreases, probably due to the redox conditions in which these long extractions are performed.  相似文献   

15.
One main problem with current research on spatio‐temporal modeling of ion fluxes in forest soils is the separation of space and time effects in the soil‐monitoring concept. This article describes an approach to overcome this weakness. Time trends of point information on soil‐solution data (base‐cation concentrations and fluxes) are scaled by linking them to soil‐chemical data which is available in higher spatial resolution and can be upscaled to an area base. This approach is based on a combined evaluation of bulk soil and soil‐solution data using both statistical and process‐oriented methods. Multiple‐linear‐regression analyses coupled with geostatistics were developed to predict spatial patterns of exchangeable cation percentages. In a second step, empirical ion‐distribution coefficients were adapted according to Gapon using data of suction‐cup plots and bulk‐soil samples. Seasonally adjusted time‐series data of soil‐solution chemistry were then connected with the maps of the predicted exchangeable‐cation percentages by means of the Gapon equations. This evaluation step provided both time‐ and space‐dependent maps of cation concentrations in the soil solution. Finally, using the results of a water‐budget model it was possible to derive spatio‐temporal patterns of soil cation fluxes. Methodological limitations and the results of verification processes are discussed. The methods described can only be used in acidic soils and should not be used in soil layers rich in humus, since adsorption to C compounds differs from adsorption to clay minerals. The time increments of the models should be not shorter than yearly in order to suppress annual periodicity. Although the Gapon equations were not based on laboratory‐determined exchange solutions at quasi‐equilibrium, but rather on field data from the suction‐cup technique, the exchangeable‐cation percentages showed steady functions of selectivity coefficients. The methods tested at a watershed scale may be flexible enough to be applied at other scales as well.  相似文献   

16.
For the survey of saline and alkali soils sampling soil solution in situ is difficult. An alternative is to take soil samples, analyse their extracts and then calculate the chemical composition of the soil solution. A model (EXPRESO) has been designed to calculate both the chemical speciation of electrolyte solution and the exchange equilibrium with an adsorbed phase during simulated dilution and concentration. EXPRESO was validated using reclaimed saline soil samples. Results demonstrated that EXPRESO is a thermodynamically coherent and mass conservative model that allows the calculation of the chemical composition of both the soil solution and the exchange complex over a large range of soil water content (0.250–5 kg water kg–1 soil). EXPRESO enables the estimation of the chemical composition of the in situ soil solution, giving a comprehensive picture of the soil status under different field conditions. Modélisation de la concentration ou de la dilution des systèmes eau-sols salés Résumé  相似文献   

17.
Abstract

In 100 different soils, hot (100C) water extractable boron was determined and the results were compared with boron data after extraction of the same soil samples with cold (20C) 0.01 M CaCl2. Since the boron concentrations in cold soil extracts are too low for direct determination, the extracted boron was converted into BF4‐ and subsequently extracted with a liquid anion exchanger, Aliquat 336, into xylene, and measured by ICP‐AES. A linear relation with R2 = 0.74 was found between the two tested procedures. It is, therefore, concluded that with a cold 0.01 M CaCl2 extraction equally valuable soil boron values can be obtained as with the more difficult to standardize hot water extraction procedure.  相似文献   

18.
Isotopically exchanged phosphorus is difficult to determine in soils that strongly sorb P (so that there is little P in solution) and in soils with large concentrations of colloidal P in soil suspensions. A method is proposed in which anion exchange membranes (AEM) are added to the soil suspension after an initial period of isotopic exchange with 32P‐labelled phosphate ions. Isotopically exchanged P, termed EAEM, is calculated from the ratio of labelled phosphate ions to the total phosphate ions on the membrane. The EAEM was compared with the E value measured in an aqueous soil extract (EWater extract) for 14 soils with different degrees of P sorption. The two methods gave similar results in soils with large P concentrations in an aqueous soil extract. However, EWater extract values significantly exceeded the EAEM values by up to 18‐fold when soluble P was near the determination limit (0.008 mg P l?1). In a second experiment, two Ferralsols received further P from inorganic and plant sources and were incubated for 7 days. Treatment effects on labile P were erroneous as detected by the EWater extract but were significant as detected with the AEM method. Third, EAEM values were followed in a Lixisol and a Ferralsol which received labelled phosphate ions with carrier just before the beginning of a 23‐day incubation. The approximate recovery of added inorganic P in the EAEM value suggested that this method adequately samples labile P in P‐sorbing soils. All these results showed that errors in the determination of E values for soils with very small concentrations of P in the soil solution are reduced using the proposed method.  相似文献   

19.
为了研究三峡调蓄过渡期长江河口地区秋季滨海滨江土壤的盐渍化状况,进行土样采集和盐分组成测定,利用统计分析软件对区域土壤盐渍化类型和特点进行主成分分析,对区域土壤盐分剖面类型进行聚类分析。分析结果表明:三峡调蓄过渡期河口地区秋季土壤以盐化潮土为主,阳离子组成Na+为主,阴离子组成SO42-型略多于Cl-型,土壤剖面盐分以上升积聚为主,盐分积聚既呈现短期盐峰又有长期积累现象,存在盐渍化趋势,并主要受干旱枯水因素影响。三峡调蓄的影响程度有待进一步研究。提出应有针对性地采取合理灌排措施和Na质盐碱土改良措施。  相似文献   

20.
Paper mill residuals may beneficially be used to improve the fertility of tropical acid soils. The effects of paper pulp on soil pH, exchangeable Al and soil solution composition of three acid tropical soils were compared with the effects of equivalent rates of lime in two batch experiments. Paper pulp was more effective than lime in increasing soil pH. However, both amendments were equally effective in decreasing exchangeable Al. Paper pulp and lime similarly influenced the composition of the soil solution by increasing soil solution pH, dissolved organic carbon, inorganic carbon, NO3, SO4, Ca and Mg. The supply of nitrate by the soil, however, was reduced in paper pulp treatments compared to lime treatments. Nitrate had a major role in controlling nutrient concentrations in the soil solution. Reduced NO3 concentrations in paper pulp treated soils compared to limed soils could therefore result in lower nutrient availability and limited losses by leaching.  相似文献   

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