Sum Of Exchangeable Cations Research Articles

Physicochemical Properties and Fertility Level of the Vertisols Surface Horizons for muskuwaari [Sorghum bicolor (L.) Moench] Cultivation in the Sudano-Sahelian zone of Cameroon

Poor agricultural practices coupled with climatic aberrations have led to the degradation of vertisols intended for muskuwaari cultivation and consequently result in a drastic drop in crop yield. Faced with this situation, the knowledge of the state of their physicochemical properties and fertility level becomes a priority to develop strategies to restore their fertility. In this perpective, this work is inscribed to contribute to the knowledge of the state of the physicochemical properties of vertisols and the evaluation of the associated fertility level. To do this, 6 samples of cultivated vertisols associated with the rhizosphere were surveyed and collected in the surface horizon (0-30 cm) including, three samples in each administrative region of the North (Houla, Bangli, Pitoa) and the Far North (Dargala, Ibba, Moutourwa) respectively. Physical characterisation revealed that almost all of these vertisols have rather a silty texture with a very small proportion of the clay fraction (25.66-28.66%) compared to normal (40-80%). Chemically, acidity is spatially variable with generally low proportions (pH= 5.50-7.16) compared to normal (7-7.5). These vertisols also have very low proportions of nitrogen (0.03-0.08 %), organic carbon (0.95-1.9%), organic matter (1.63-3.39%), C/N ratio (19.45-49.14%), assimilable phosphorus (5.92-45.31 mg/kg), the sum of exchangeable cations (4.10-7.56 meq/100 g), cation exchange capacity (16.51-18.49 meq/100 g) and saturation of the exchangeable complex (23.33-43.14%) compared to normal especially for organic matter (2-4%), the sum of exchangeable cations (25-40 meq/100 g), the cation exchange capacity (20-45 meq/100 g) and the saturation of the exchangeable complex (80-100%). Therefore, the fertility level associated with these vertisols was very low with at least one limiting parameter. One fertility rehabilitation strategy for these vertisols is based on the use of inputs such as mycorrhizae and/or compost.

Assessment of fallow grey forest soils fertility in sub-taiga zone of Omsk Priirtyshye

There is a need to obtain information on the current state of their properties when reintroducing fallow soils into arable land. The aim of the research was to study fertility indicators of grey forest soils (Luvic Greyzemic Phaeozems) The research area was located in the city of Tara, Omsk region (south of Western Siberia). A field survey of soils and vegetation cover was carried out in plots with different age of fallow land with the establishment of the value of the above ground mass. The results of the research showed that the fallow area with age of less than 10 years is represented by a thick grey forest soil, with age of 10-20 years - by a medium thick grey forest soil. The value of air-dry aboveground mass of plants varied from 1.01 to 1.01 2.58 t/ha. High density, low porosity, and aeration porosity were found in soils throughout the profile. The humus content and reserves in soils are low and average; its distribution in profiles is markedly decreasing. Reaction of soil medium is acidic (рН=4.4-4.8). The sum of exchangeable cations in humus horizons is elevated and high. In composition of cations calcium prevails (71.5-74.9 %) with magnesium share - 22.4-26.9 % and insignificant content of sodium (1.6-2.5 %). The surveyed soils can be reintroduced to arable land. However, it is necessary to provide measures to reduce acidity, improve organic matter balance, reduce density, and increase porosity of upper and subsoil horizons.

English

Arbuscular mycorrhizal fungi (AMF) are organisms that can establish symbioses with 80% of terrestrial plants. Soils were collected in three agroecological zones (AEZ) of the Central African Republic (CAR). The aim of this research is to study the diversity of AMF in the CAR. The spore extraction and enumeration, granulometric and physicochemical analyses of each soil were performed. The results showed that AEZ3 has a large number of spores; it is therefore the densest followed by AEZ2 and AEZ1. The particle size analysis showed that AEZ1 and 2 have a sandy-clay texture and AEZ3 is sandy-silty. The average water pH of the three surveyed areas is 5.13. The organic matter content is low. The total nitrogen content of the soils varies from one area to another. The C/N ratio of the studied soils varies from 9.65 to 15.5 with an average of 13.8. The total phosphorus content is lower than the norm. The best calcium content is obtained in AEZ3 followed by AEZ1. Magnesium, sodium, the sum of exchangeable cations and cation exchange capacity (CEC) were below the critical thresholds.   Key words: Diversity, Arbuscular mycorrhizal fungi (AMF), agroecological zones, Central African Republic.

Near-infrared, mid-infrared or combined diffuse reflectance spectroscopy for assessing soil fertility in rice fields in sub-Saharan Africa

Assessment and monitoring of soil resources is needed for ensuring environmental sustainability of rice production in sub-Saharan Africa (SSA). Diffuse reflectance spectroscopy has the potential to offer means to evaluate and monitor soils at large scale in an efficient, affordable and timely manner. However, its accuracy for predicting chemical and physical properties of soils under rice cultivation is little known. The objectives of this study were to i) determine physical and chemical soil fertility properties which can be accurately analyzed using near infrared (NIR) (700–2500 nm), mid-infrared (MIR) (2500–16,670 nm), or a combination of both (NIR-MIR) (700–16,670 nm) spectral libraries, ii) compare their prediction potential for identifying the most suitable spectral range for simultaneous analysis of soil fertility properties, and iii) assess degrees of variation of 29 soil fertility properties for 2845 soil samples collected from 42 study sites in 20 SSA countries. Diffuse reflectance spectroscopy data were obtained using a Fourier-transform infrared spectrometer (FT-IR) Tensor 27 with a high-throughput screening (HTS-XT) extension unit. About 10% of the whole sample set was chosen for conventional wet chemistry soil analysis, and was used for developing best fitted models with partial least squares regression (PLSR) that can estimate soil fertility properties using infrared (IR) spectra. The prediction performances were evaluated by R2, RMSE and RPIQ. Good prediction models (0.75 < R2 ≤ 0.86 and 1.36 ≤ RPIQ ≤ 3.78) were obtained for 13 soil properties consisting of pH H2O 1:2, exchangeable Ca, exchangeable Mg, sum of exchangeable cations, CEC, ECEC, base saturation percentage, total N, total organic C, clay content, silt content, phosphorus sorption index (PSI) and extractable Al. Satisfactory predictions (0.53 ≤ R2 ≤ 0.75 and 0.59 ≤ RPIQ ≤ 2.56) were obtained for pH H2O 1:2.5, exchangeable K, extractable Mn, Cu, and B, and sand content. NIR, MIR, and combined NIR-MIR diffuse reflectance spectroscopy demonstrate the best prediction potential for 14, 21, and 76% of the studied soil fertility properties, respectively. Except soil pH, most of soil properties are moderate to highly variable (CV = 21–131%). On average, soils in rice fields are characterized by moderate acidity, and low total N, available P and B. In conclusion, the combined NIR-MIR diffuse reflectance spectroscopy can offer an alternative to conventional wet chemistry methods for assessing soil fertility properties in rice fields in SSA, except for those having poor prediction potentials.

Transformation of Trioctahedral Mica in the Upper Mineral Horizon of Podzolic Soil during the Two-Year-Long Field Experiment

An experiment on transformation of biotite (fraction <1 μm) particles placed into containers with different permeability in the AEL horizon of podzolic soil was performed in order to estimate the contribution of different factors to the transformation of biotite in the modern soil. After two-year-long incubation in the AEL horizon, biotite was transformed into vermiculite, mixed-layer biotite–vermiculite, and pedogenic chlorite. The most intense vermiculitization of the biotite took place under the impact of fungal hyphae and, to a lower degree, fine plant roots and components of the soil solution. The formation of labile structures from biotite was accompanied by thinning of the mica crystallites, the disturbance of the homogeneity of layers, the removal of interlayer K, the removal and oxidation of octahedral Fe, the increase in the sum of exchangeable cations, and the appearance of exchangeable Al. The process of chloritization was definitely diagnosed upon the action of plant roots and fungal hyphae on the biotite. Strong complexing anions released by fungal hyphae partly inhibited chloritization. Chloritization led to a decrease in the cation exchange capacity of vermiculitic structures.

Changes in Soil Quality by Compost and Hazelnut Husk Applications in a Hazelnut Orchard

ABSTRACTIn this study, changes in some soil quality indexes in a hazelnut orchard located in the Black Sea Region of Turkey were investigated after 6 months of compost (CMP) and hazelnut husk (HH) applications. CMP and HH applications increased soil organic carbon (OC) content from 1.40% to 2.57 and 3.51%, and electrical conductivity from 0.06 dS m−1 to 0.20 and 0.91 dS m−1, respectively (P < 0.01). In comparison to control treatment, CMP and HH applications increased the sum of exchangeable cations by 31 and 37%, aggregate stability by 2 and 7%, initial infiltration rate by 34 and 436%, and reduced bulk density by 20 and 33%, penetration resistance by 33 and 67%, respectively (P < 0.01). Physical and chemical soil quality parameters were improved using both HH and CMP in the hazelnut orchard. Although both organic matter sources were effective on quality of clay soil, slow mineralization rate of HH in soil due to including the highest C:N ratio (55%) caused greater effects of HH on soil quality indexes than that of CMP (having 22% C:N ratio) after 6 months of application.

A Comparison of Methods for the Determination of Cation Exchange Capacity of Soils/Porównanie Metod Oznaczania Pojemności Wymiany Kationów I Sumy Kationów Wymiennych W Glebach

Abstract The object of this study was to compare the results obtained with four methods of determination of cation exchange capacity (CEC) and sum of exchangeable cations (Ca, Mg, K) in soils. One of these methods is Kappen’s method and the others methods are based on different extracting reagents: sodium acetate (pH = 8.2), barium chloride and hexaamminecobalt(III) chloride. Values measured with barium ions and hexaamminecobalt(III) ions as index cations are very comparable and these two methods can be considered as equivalent. Kappen’s method gives overestimated results, especially for acid soils reach in organic matter and very calcareous soils. Sodium acetate, buffering the pH of the extracting solution, causes increase of numbers of negatively charged sites and particularly those bonded to organic matter and for this reason values obtained with this method are overestimated. Nevertheless, it is possible to correct this error for a given soil sample by regression equation considering pH of soil, clay and organic carbon content.

Effects of tillage, fallow and burning on selected properties and fertility status of Andosols in the Mounts Bambouto, West Cameroon

To assess the impact of land use on the Andosol fertility, changes in chemical and physical properties affecting soil quality were monitored on Andosols from Mount Bambouto submitted to four different land use and management systems: natural cover, tillage, burning and fallow. In comparison with the natural cover, tillage reduces Andosol OC (6.5 to 4.8%), total N (4.51 to 2.95‰), CEC (22.0 to 20.9 cmol.kg–1) and the abundance of soil macro-aggregates expressed by the water stable aggregates (WSA) varies from 53.8 to 12.0%; and increases the bulk density (0.69 to 1.09 g.cm–3) and the sum of exchangeable cations (3.58 to 4.84 cmol.kg–1). Burning also reduces Andosol OC (6.5 to 0.8%), total N (4.51 to 0.95‰) and CEC (22.0 to 10.2 cmol.kg–1), but increases soil pH (4.62 to 6.54), the sum of exchangeable cations (3.58 to 5.74 cmol.kg–1) and the abundance of soil macroaggregates (WSA: 38.2 to 57.0%). In comparison with tillage, fallow increases Andosol OC (4.8 to 6.5%), total N (2.95 to 5.04‰), CEC (18.0 to 21.6 cmol.kg–1), the sum of exchangeable cations (3.58 to 5.05 cmol.kg–1) and the abundance of soil macroaggregates (WSA: 12.0 to 48.8%). Globally, the tillage management deteriorates Andosol chemical and physical properties affecting fertility, whereas the fallow management restores them. The burning management also improves some Andosol chemical and physical properties affecting quality, but it won’t last long.

Three new, quick CEC methods for determining the amounts of exchangeable calcium cations in calcareous clays

AbstractThe cation exchange capacity (CEC) is one of the most important properties of clays in terms of their performance in both natural and technical processes. For decades, common methods for determining exchangeable cations have failed when calcareous clays or soils were examined, because calcite is at least partly dissolved throughout the exchange experiment which in turn increases measureable Ca2+ concentrations. As a result, exchangeable Ca2+ and the sum of exchangeable cations by far exceed the amount of negative charges. In the past, the silver-thiourea method (AgTU) has been modified to overcome this problem (AgTUcalcite), but is unsatisfactory as the method is laborious. In the present study three new methods based on two alternative metal complexes, cobalt(III) hexamine (CoHex) and copper(II) triethylenetetramine (Cu-trien), are proposed. The optimum solid/liquid ratios of these methods and the optimum complex concentration of Cu-trien are reported, depending on the mineralogical composition of the samples. The key development is that the exchange solutions are saturated with respect to calcite prior to the experiment. Approximately 70–90% of the dissolution of calcite present as an admixture in a clay sample is suppressed in the subsequent cation exchange experiment, but not all. The Ca2+ exchange is not suppressed and there is no evidence for any precipitation of this Ca2+. Three possibilities for how to handle this problem are discussed, one of which is to perform no further correction. The resulting error arises from the remaining calcite solubility of the different solutions after pre-treatment with calcite. This corresponds to errors of 0.2–1.3 (CoHexcalcite)and 0.7–8.4 (Cu-triencalcite) meq/100 gCa2+ for samples with small and large CEC values, respectively. As a consequence of the poor performance of Cu-triencalcite for samples with large CEC, a more concentrated Cu-trien5 × calcite solution was developed which performed much better: 0.1–0.8 meq/100 g(Cu-trien5 × calcite). For Cu-trien5 × calcite and CoHexcalcite at least, the errors are in the range of the non-systematic scattering for exchangeable Ca2+ determination. Therefore, the methods suggested provide ‘operationally correct’ Ca2+ values without additional effort. Moreover, owing to the high selectivity of the index cations applied in the present study, only one exchange step is required, providing a significant advantage over the AgTUcalcite method.

Evaluating near infrared spectroscopy for field prediction of soil properties

This paper demonstrates the application of near infrared diffuse reflectance spectroscopy (NIR-DRS) measurements as part of digital soil mapping. We also investigate whether calibration functions developed from a spectral library can be used for rapid characterisation of soil properties in the field. Soil samples were collected along 24 toposequences in the Pokolbin irrigation district, ~7 km2 of predominantly agricultural land in the Hunter Valley, NSW, Australia. Soil samples at 2 depths: 0–0.10 and 0.40–0.50 m were collected. The soil samples were scanned using NIR under 3 different conditions: field condition, dried unground, and dried ground. A separate spectral library containing soil laboratory measurements was used to develop functions to predict 3 main soil properties from NIR spectra (total C content, clay content, and sum of exchangeable cations). The absorbance spectra were found to be different for the 3 soil conditions. The field spectra appear to have higher absorbance, followed by dried unground samples and then dried ground samples. Although most spectral signatures or peaks were similar for the 3 soil conditions, field samples appear to have higher absorbance, particularly at 1400 nm and 1900 nm. The convex hull of the first 2 principal components of the soil spectra is an easy tool to evaluate the similarity of spectra from a calibration set to an observation. For field prediction, samples need to be calibrated using field samples. Finally, this study shows that NIR-DRS measurement is a useful part of digital soil mapping.

Fine root mineralization, soil organic matter and exchangeable cation dynamics in slash and burn agriculture in the semi-arid northeast of Brazil

The objective of this study was to understand the causes of crop productivity decline on a soil cultivated by the slash and burn method. The contribution of ashes, fine roots, and soil organic matter (SOM) mineralization to the pool of available nutrients of a nutrient-poor Haplustox of the semi-arid zone of northeastern Brazil was documented. Ashes were the most important input of nutrients to the soil. The burning of the vegetation debris produced 11 Mg ha −1 of ash containing considerable quantities of Ca and K, and some N, Mg and P. The ashes, in general, contained more Ca and Mg, and less N and K, than the estimated requirements of the cassava ( Manihot esculenta) crop during the cultivation cycle, whereas the P in ashes was equivalent to the crop P uptake. About 65% of the fine roots from the native vegetation decomposed in the soil during the first rainy season after the slash and burn, contributing Ca, N, and Mg to stores of available nutrients, with limited supply of K and P. The SOM content decreased with cultivation. The losses ranged from 4 to 16%, 6–18%, and 10–20%, for C, N and organic P, respectively. The sum of exchangeable cations, base saturation and pH increased after the burn, whereas the exchangeable Al and Al saturation strongly decreased, promoting better growing conditions for the cassava crop, particularly during the first years of the cultivation cycle. The soil properties reverted to pre-burn conditions within two or three crop years, productivity declined and the field was abandoned to natural fallow.

Changes in soil chemistry associated with changes in soil-pH in Victorian pastures

Relationships between changes in soil pH and changes in other soil chemical properties were examined using data from a survey of 107 pasture sites from across Victoria. At each site, soil samples (0-5, 5-10, 10-15 and 15-20 cm depths) were taken from the pasture and an adjacent undisturbed (reference) area for chemical analysis. Changes in soil chemical properties were inferred from differences between pasture and reference soils. Increases in extractable Al and extractable Mn and decreases in the sum of exchangeable cations were associated with decreases in pH. Changes in soil organic C, total soil N and total soil P were not associated with changes in pH but were related to pasture composition at each site. Increases in total soil P and exchangeable Ca, and decreases in exchangeable Mg were partly attributed to the application of superphosphate. Decreases in electrical conductivity are discussed in relation to vegetation and salinization.

Andisol formation in a Holocene beach ridge plain under the humid tropical climate of the Atlantic coast of Costa Rica

Soil formation has been studied in relation with time in a 5000-year old chronosequence on volcaniclastic beach ridges of the perhumid tropical Atlantic coast of Costa Rica. All soils are under tropical rainforest. Drainage conditions change by subsidence from excessively drained in the two youngest soils to imperfectly drained in the two oldest soils. Parent material is rather homogeneous andesitic sand with a volcanic glass component of less than 10%. It has been found that under these conditions Andisols form within 2000 years. Imperfect drainage caused mottling and accumulation of iron-coatings, as well as the formation of a thin O-horizon in the oldest profiles. Sand content of the soils decreases regularly with soil age, while the amount of fine material increases concurrently. The increase in fine material and the accumulation of organic matter cause an increase of CEC and andic properties, and a decrease in bulk density and pH with soil age. Depth of biological influence increases with soil age, but soil faunal activity is hampered in the oldest three profiles, probably by imperfect drainage. Due to the extreme leaching conditions, the sum of exchangeable cations is less than 2 cmol + kg −1 in the B-horizons of the older soils, notwithstanding the presence of a considerable amount of weatherable primary minerals.

Changes in effective cation exchange capacity and exchangeable aluminum with soil pH in lime-amended field soils

Eleven acidic soils from northern N.S.W., having a wide range of values for ECEC, A1 and soil organic carbon (%C), were treated in the field with five rates of lime. The relationships between soil pH and the effective cation exchange capacity (ECEC), and between pH and exchangeable aluminium (Al), were investigated for the top 10 cm of these soils. Increases in the total exchangeable cations (TEC) calculated as ECEC-Al, were shown to be madelup almost entirely by increases in exchangeable calcium. There were no consistent changes in the amount of exchangeable magnesium, potassium or sodium due to liming these acidic soils. Formulae used to predict changes in A1 and ECEC with pH in the 'Lime-it' model were tested and modified on the 11 soils from northern N.S.W. A strong linear relationship was observed in each soil between Al and pH (transformed to hydrogen ion concentration x 103). The slope of this relationship (SALs) can be predicted from the pH and A1 values of unlimed soils. Strong linear relationships were also observed between pH and TEC, for each of the 11 soils. The SL, (the slope of the linear relationship TEC/pH for any soil 's') was shown by multiple regression analysis to be a function of TECi/pHi (where TECi is the sum of exchangeable cations of unlimed soil 's'; and pHi is the pH value of unlimed soil 's'), %C of the unlimed soil, and SALs. By using the measured values of pH, ECEC, Al and %C of unlimed soils, the values of Al, and TEB can be predicted for any pH value that may be measured (or predicted) after liming. The predictive relationships developed on N.S.W. soils were tested against independent data from New Zealand. The results confirmed the Al/pH predictions (R2 = 0.955), while the TEC/pH predictions were less well matched (R2= 0.62) possibly due to unusual clay mineralogy or organic matter fractions of 3 of the 18 soils tested.

SOME SIERRA LEONE SOILS

We studied 11 representative pedons from four physiographic groups. When Feoxide was removed before particle-size analyses, the percentage of clay was higher than when Fe-oxide was present. It was also commonly higher than clay estimated by the factor 2.5 x 15 bar moisture content. Therefore, 2.8 would be a more suitable factor than 2.5. The criterion, sum of exchangeable cations x 100/clay % ≤ 12 meq does not alone separate the oxic or kandic horizons from other diagnostic horizons of the soils studied. All pedons studied met this criterion. The criterion CEC x 100/clay % ± 16 meq was somewhat more useful. One soil narrowly failed to meet this limit, until 2.8 was used instead of 2.5, as suggested above. A critical value of about 0.09 for the ratios: %Fe2O3-d/clay % and %Fe2O3-d minus %Fe2O3-o3/clay % may help to separate oxic and nonoxic horizons.5

A rapid method to determine cation exchange capacity and exchangeable bases in calcareous, gypsiferous, saline and sodic soils

Summary A simple, single‐step extraction with LiEDTA for the estimation of CEC and exchangeable bases in soils has been developed. Multivalent cations are stripped from the soil adsorption sites by the strongly chelating agent EDTA, and are replaced by Li. In soils without CaCO3 or water soluble salts, exchangeable divalent cations (Ca, Mg) are chelated by EDTA and exchangeable monovalent cations (Na, K) are replaced in a single extraction step using 0.25–2.5 g of soil and 10.0 ml of extractant. In calcareous soils the CEC can be determined in the same way, but for the extraction of exchangeable Ca and Mg, another separate extraction is needed because dissolution of calcite by EDTA is unavoidable. This extraction is done with as much NaEDTA as needed to extract only exchangeable Ca and Mg in a 1:2 (m/V) soil/alkaline‐50% (V/V) aethanolic solution to minimize dissolution of calcite. In gypsiferous soils gypsum is transformed into insoluble BaSO4 and soluble CaEDTA by LiBaEDTA thus avoiding interference of Ca from dissolution of gypsum, which renders the traditional methods for determining CEC unsuitable for such soils. To determine exchangeable Ca and Mg, Na4EDTA is used as for calcareous soils. In saline/sodic soils replacement of Na by Li is incomplete but the Na/Li‐ratio at the complex after extraction is proportional to the molar Na/Li‐ratio in the extracts, so that the CEC and original exchangeable sodium (ESP) content can be calculated. Additional analysis of Cl and, if necessary, SO4 in the extracts of saline soils can be used to correct for the effect of dissolution of the salts on the sum of exchangeable cations. This new method is as convenient as the recently developed AgTU (silverthiourea), but is better suitable for calcareous and gypsiferous soils.

Cation exchange capacity of roots: Titration, sum of exchangeable cations, copper adsorption

Abstract The cation exchange capacity of roots (CECR) has been measured according to three different methods : titration of H‐roots with NaOH in the presence of CaCl2, MgCl2, or NaCl 0.1 N, saturation of roots with mixed Ca‐Mg‐Na solutions of eight different compositions and extraction of the adsorbed cations with copper, saturation of roots with Cu‐ions and extraction with HC1. Two types of roots were studied : roots of ryegrass (Lolium multiflorum Lm.) and roots of clover (Trifolium pratense L.) The very good coincidence of the results from the three methods tends to prove the reliability of the experimental procedures. The simplicity and the reproducibility of the Cu‐method renders it recommendable in view of possible standardization of the methods in the future.

Aqueous Geochemistry and the Exchangeable Cation Composition of Glauconite in the Aquia Aquifer, Maryland

ABSTRACTThe cation composition of water in the Aquia aquifer of southern Maryland changes systematically in the direction of ground‐water flow. In the upgradient parts of the aquifer, calcium is the dominant cation in solution. Between 10 and 20 miles downgradient, calcium and magnesium are dominant. Between 20 and 35 miles downgradient, magnesium and potassium are dominant, and, beyond 40 miles downgradient, sodium is the most abundant cation in solution. The exchangeable cation composition of glauconite in the Aquia aquifer changes systematically in the direction of flow in a manner similar to the changes in water chemistry. These observations are interpreted as evidence that cation exchange reactions are processes that simultaneously alter water composition and glauconite composition along the flowpath.Exchange parameters K’and n for glauconite in the Aquia aquifer were determined for the reactions: image image image The exchange parameters for each reaction were tested by an indirect method. Molar ratios of exchangeable cations or glauconite were calculated from water chemistry data using the derived k’and n values. In each case, the trend of calculated molar ratios compared favorably with measured molar ratios. The calculated exchange parameters demonstrate that the exchange process is not linear for the Ca2+ ‐Na+ and Mg2+ ‐Na+ ion pairs.The sum of exchangeable cations on glauconite samples is significantly lower in the outcrop area than downgradient. Corresponding to this, the concentration of dissolved silica and dissolved oxygen in Aquia water is high near the outcrop area and decreases downgradient. This pattern suggests that incongruent dissolution of glauconite is an additional process that modifies glauconite composition near the outcrop area but is less important downgradient.

THE USE OF pH-DEPENDENT CATION-EXCHANGE CAPACITY FOR CHARACTERIZING THE B HORIZONS OF BRUNISOLIC AND PODZOLIC SOILS

A study was made of the pH-dependent C.E.C. as a means of characterizing and differentiating the B horizons of Brunisolic and Podzolic soils. The pH values were measured in 0.01 M CaCl2 after which the soils were extracted with Nacl to determine the percentage base saturation and sum of exchangeable cations. The total C.E.C. values were determined with Ca(OAc)2 + CaCl2 at pH 7 of the untreated soil and of the soils after H2O2 treatment, after extraction with acid ammonium oxalate, and after heating at 200 °C in an atmosphere of N2. The pH-dependent C.E.C. represented by the difference between the C.E.C value determined with Ca(OAc)2 + CaCl2 and the sum of cations extracted with NaCl was found to be small for the B horizons of Brown Forest and Brown Wooded soils. The B horizons of Podzol, Humic Podzol, Acid Brown Wooded, Concretionary Brown, and some Acid Brown Forest soils had high pH-dependent C.E.C. The horizons with high pH-dependent C.E.C. contained significant quantities of amorphous sesquioxide–organic complexes as shown by their relatively high organic matter and free sesquioxide contents and by their exchange properties. The pH-dependent charge appeared to be as effective a primary chemical means of characterizing horizons with spodic properties as were techniques based on the effects of free oxide extraction or heating in N2 on the exchange capacity.