Variation In Cation Exchange Capacity Research Articles

Fertilisation with P, N and S requires additional Zn for healthy plantation tree growth on low fertility savanna soils

Context Soil nutrient limitations characterise savanna soils globally and are one of several constraints to establishing productive tree plantations and enhancing economic opportunities in tropical regions. Fertilisation offers an approach to overcome soil nutrient limitations to maximise tree growth and health, but requires research on nutrient contents, composition, rates and methods of delivery in the context of soil characteristics. Aims To determine the optimal contents, rates and methods of application of fertiliser to maximise the growth and health of the plantation timber species Pinus caribaea on low fertility savanna soils. Methods Factorial field experiments tested growth responses to applications of phosphorus (P), nitrogen (N) and sulfur (S) on three soils near Darwin, Australia. Further experiments tested effects of zinc (Zn), copper (Cu) and potassium (K) application and small-scale variation in soil characteristics on tree performance. Key results Positive growth responses to P, N and S were recorded, yet unhealthy trees developed, particularly in better-performing treatments. Second phase experiments addressing potential causes of ill health confirmed Zn limitations. Intense spatial soil sampling demonstrated substantial variation in cation exchange capacity and composition over short distances. Conclusions Nutrient additions to enhance plantation tree growth will need to encompass minor and trace elements in addition to N, P and S, specifically Zn, and consider the mechanism of application. Implications Small-scale variability in cation exchange capacity and composition indicates that optimal fertilisation rates will vary spatially, and that soil sampling for site characterisation would be more accurate with replicated dispersed samples.

Compositional-structural characterization of the Opalinus Clay and Passwang Formation: New insights from Rietveld refinement (Mont Terri URL, Switzerland)

Middle Jurassic Opalinus Clay (OPA) in Switzerland and Southern Germany is considered as host rock for the disposal of heat-generating radioactive waste. For the present study, core samples from the Mont Terri rock laboratory (Switzerland) were investigated using a facies-based approach including mineralogical and geochemical analyses. Special focus was on the analysis of the degree of ordering of irregular illite-smectite interstratified clay minerals (I-S) responsible for sorption of radionuclides and swelling properties of the rocks.The investigations support the classification of OPA into five main facies (instead of the established threefold division) and into further subfacies. The facies concept was extended to the Passwang Formation (PWF). The amount of clay fraction varies in samples from the different facies, which is consistent with variations in cation exchange capacity (CEC). X-ray diffraction (XRD) analyses of the <2 μm fraction revealed a homogenous composition of the main constituents, namely R1-ordered I-S, kaolinite, and illite. Crystal structure based Rietveld refinement indicates strong similarities in the nature of disorder of the interstratified illite-smectite minerals for all investigated facies. The I-S-phase can be described with the R1 model, which is together with the amount of illitic layers in the I-S an indicator for a maximum burial temperature between 90 and 105°C. The amount of illitic layer in the I-S varies from 73%–85% for all refinements and ordering types, and in all OPA and PW facies and subfacies. This, together with the homogenous composition of the clay size fraction points to (1) a homogenous overprint of the clay assemblage during burial and/or (2) a uniform siliciclastic sedimentary supply throughout the sedimentation period of the OPA. The results of this study highlight the need to combine lithofacial studies with mineralogical investigations in order to adequately capture the variability of clay-rich host rocks under consideration for radioactive waste disposal.

EFFECT OF TERMITES (GNATHAMITERMES Perplexus) INFESTATION ON SPATIAL VARIATION OF SOIL PROPERTIES AND HORTICULTURAL CROPS GROWTH

The study was conducted to evaluate the effect of termites (Gnathamitermes perplexus) infestation on spatial variation of soil properties and horticultural crops growth in Alkaleri Local Government area of Bauchi State, Nigeria. A total of 68 soil samples were collected from two (2) location; 34 each from termites infested area and in a location without termite’s infestation. Results showed that the soils were characterized by very low to medium organic matter content, very low to low levels of nitrogen content, available phosphorus range between low and high, exchangeable bases (calcium, magnesium) in both soils ranges between very low and low, Sodium content ranges between medium and high with only slight variation in Cation exchange capacity (CEC). Results of soil analysis further revealed that pH (water) and pH (CaCl2) of both soils of the study area were acidic in nature. Correlation analysis showed that there was positive and significant relationship between pH versus CEC at 0.044**; organic matter versus CEC at 0321**; and calcium versus CEC at 0.909**. Correlation was again significant at P≤0.05 levels between available phosphorus versus calcium at 0.307* and available phosphorus versus CEC at 0.263*. T-test carried out revealed that the activities of termites in the infested soil placed the nutrients status higher compared to the surrounding soils without termites infestation. The study concluded that termite’s activities have also affected the lateral and spatial variation of both chemical and physical soil properties and horticultural crops growth in the research area. The study recommended that government, cooperate organizations and private individuals should encourage and provide adequate funding for a further research in both soils and horticultural crops infested with termites and farmers be enlightened to adopt modern techniques and skills for soil and fertility management.

An algorithm to calculate the cationic composition of soil solutions. 1. Theory and structure

Difficulties forecasting cation exchange processes may limit the use of soil solution analyses in routine soil testing for agriculture. An important part of those difficulties is the need for much data and expertise to parameterise existing models that can be used for variable charge soils. This paper proposes an algorithm to simulate concentrations of the major nutrient cations in the soil solution. It is designed to have only modest data requirements, be applicable for variable charge soils, and be simple to implement in crop and environment simulation packages. It is based on a Gaines–Thomas type approach to cation exchange, adapted to allow for variations in cation exchange capacity. It includes interactions with anions and anion exchange, which may affect cation behaviour in variable charge soils. Assumptions and limitations of the approach are described, and some issues associated with parameterisation, implementation, and future extension are discussed.

Assessment of spatial variability of cation exchange capacity with kriging and cokriging

Cation exchange capacity (CEC) is one of the most important soil attributes which control some basic properties of soil such as acidity, water and nutrient retaining capacity. However, the measurement of cation exchange capacity in large areas is time consuming and requires high expenses. One way to save time and expenses is to use simple soil covariates and geostatistical methods in mapping CEC. Therefore, the aim of the present research was to investigate the role of soil covariates in the improvement of spatial variability of CEC. The study area is located in southwest Iran on the Aghili plain, Gotvand, Khuzestan province. In this study, ordinary kriging and cokriging methods were used to predict CEC. 107 soil samples were gathered on a random grid of 200-700 m. 74 samples were used for training and 33 samples for testing the results. A principle component analysis was performed for covariate selection. Clay was selected as a covariate in cokriging due to high correlation between clay and CEC[FE1] in the first principle component analysis. Based on the cross validation result of predicted dataset, RMSE and ME for cokriging were 2.16 and 0.03 cmol (+)/kg respectively, and 3.36 and 0.09 cmol (+)/kg for kriging, respectively. Based on these results, cokriging performed better than kriging for predition of cation exchange capacity since it used a covariate such as clay, for the improvement of CEC spatial prediction.

Soil slaking sensitivity as influenced by soil properties in alluvial and residual humid tropical soils

In the humid Caribbean region characterized by high-intensity tropical rainfall, soil aggregate breakdown and pore blocking due to slaking pressures are major land degradation mechanisms. In this research, we investigated the susceptibility of soils to slaking pressures under rapid wetting as influenced by soil properties and the depositional origin from which the soil is formed using water-stable aggregates (WSAr) and percolation stability (PSc) as indices of the strength of aggregate inter-particle cohesion. Wet sieving and percolation stability analyses were employed to investigate WSAr and pore blocking, respectively. The combined effect of soil properties of clay, organic matter (OM), cation exchange capacity (CEC), and exchangeable sodium percentage (ESP) was used to determine the slaking sensitivity score (SSc) of 14 physiogeographically important soils in Trinidad, comprising of nine alluvial and five residual soils. Results showed that irrespective of alluvial or residual depositional nature of the parent material, samples had high SSc with an average WSAr of 37.8% and PSc of 6.0 mm/10 min. The linear relationships between SSc with WSAr (r2 = − 0.12) and SSc with PSc (r2 = − 0.012) of all the 14 soils although negative were weak. Clay content accounted for 94.0% of the variation in CEC in alluvial soils and had strong negative relationships with WSAr (r2 = − 0.74) and PSc (r2 = − 0.79) in residual soils. Additionally, OM with WSAr (r2 = 0.52) and PSc (r2 = 0.24), and CEC with WSAr (r2 = 0.46) and PSc (r2 = 0.39) showed significant positive linear relationships in residual soil. The predominantly micaceous and kaolinitic clay mineralogy of these soils, coupled with the low OM contents, increases the proneness of the soils to slaking. This suggests that clay mineralogy is responsible for the high slaking sensitivity rather than clay content or just the depositional origin of the soils. As CEC increases, an accompanying increase in OM is required to increase inter-particle cohesion and to impart partial hydrophobicity, which in turn decreases mineralogically induced susceptibility of individual aggregates to slaking.

Variability of Cation-Exchange Capacity (CEC) of Fen Peats in Vertical Profiles from Eastern and Central Poland in Relation to Function of Peatlands as Natural Geological Barriers

Abstract An analysis of cation-exchange capacity(CEC) variability of peats is presented in vertical pro files from eastern and central Po land. CEC values were com pared with ash con tent (Ac), pH and CaCO3 content. Eight peatlands were selected for re search in the fol lowingareas: War saw Plateau (2 objects), Siedlce Plateau (2 objects), Lubartów Plateau (2 objects), Nałęczów Table land (1 object) and Dobrohusk Depression (1 object). The peatlands represented a fen peat type of similar botanic compositions of sediments, but they differed in the area, peat thickness and drain age conditions. Characteristic regular i ties in CEC variability were noted in the peatlands and there were three types of CEC variability in vertical pro files. Carbonate peats (types 1 and 2) had the high est pH and definitely the high est values of CEC. In vertical pro files, there was also a zonation, but the regularities similar to non-carbonate peats were not observed. Different distribution of phys i cal and chem i cal parameters were establishedin vertical pro files in partly drained peatlands (with a muck layer on top) with non-carbonate peats (type 3) and there were three distinct zones in vertical pro files, with different Ac and CEC. Determination of the vertical CEC variability and other phys i cal and chem i cal parameters in peatlands made it possible to distinguish zones with potentially most beneficial isolation conditions.

Characterization of floodplain soils in Southern Guinea Savanna of North Central Nigeria

The study was set up to characterize floodplain soils of Southern Guinea Savanna in North Central Nigeria for sustainable land use. The flexible grid method was adopted to identify the soil units. Soil map was produced in a GIS environment, using morpho-physical and soil chemical properties. The major morphological expressions are ferrolyses and gleization. The variation in cation exchange capacity recorded (1.29–21.64cmolkg−1) could be attributed to effects of various deposits of soil regoliths from time to time. The phosphorus distribution is generally low (0.8–11.8mgkg−1) while nitrogen content is >0.15% at the surface. The major pedogenetic processes include cummilization, ferrolyses and gleization. The soil units identified were classified as Fluvaquentic Epiaquept, Aquertic Ustifluvent, Kandic Ustifluvent, and Aeric Ustipsamment. The mapping units suggest two possible management units based on texture and chemical properties. The soils are generally suitable for rice production due to epi-saturation.

Influence of long-term application of composted or stockpiled feedlot manure with straw or wood chips on soil cation exchange capacity

ABSTRACTThe influence of annual applications of composted (CM) or stockpiled (SM) beef feedlot manure with straw (ST) or wood-chip (WD) bedding on cation exchange capacity (CEC) of a clay loam soil in southern Alberta was examined after 1, 8, and 15 years. The hypotheses in our study were that soil CEC should be greater for amended than unamended soils; manure type and bedding should have no effect on soil CEC; and soil CEC should increase with greater manure application rate. After fifteen applications, the CEC was significantly greater for amended than unamended soils. Manure type had no significant (P > 0.05) effect on soil CEC after fifteen applications, and the mean soil CEC was 5% greater for WD than ST. Mean CEC was significantly greater by 7 to 12% for the 77 than the 13 and the 39 Mg ha−1 rates after fifteen applications. The soil CEC was increased by 0.061 cmolc kg−1 for a unit increase in application rate (Mg dry wt. ha−1 yr−1), and 96% of the variation in CEC for amended soils could be explained by application rate. Overall, bedding, rate, or adjusting both bedding type and manure rate (but not manure type), may be possible practices for feedlot producers to manage soil CEC.

Influence of Pine Bark Particle Size and pH on Cation Exchange Capacity

Cation exchange capacity (CEC) describes the maximum quantity of cations a soil or substrate can hold while being exchangeable with the soil solution. Although CEC has been studied for peatmoss-based substrates, relatively little work has documented factors that affect CEC of pine bark substrates. The objective of this research was to determine the variability of CEC in different batches of pine bark and determine the influence of particle size, substrate pH, and peat amendment on pine bark CEC. Four batches of nursery-grade pine bark were collected from two nurseries, and a single source of sphagnum moss was obtained, separated in to several particle size classes, and measured for CEC. Pine bark was also amended with varying rates of elemental sulfur and dolomitic limestone to generate varying levels of substrate pH. The CEC varied with pine bark batch. Part of this variation is attributed to differences in particle size of the bark batches. Pine bark and peatmoss CEC increased with decreasing particle size, although the change in CEC from coarse to fine particles was greater with pine bark than peatmoss. Substrate pH from 4.02 to 6.37 had no effect on pine bark CEC. The pine bark batch with the highest CEC had similar CEC to sphagnum peat. Amending this batch of pine bark with sphagnum peat had no effect on composite CEC.

Variations in Stand Structure and Diversity along a Soil Fertility Gradient in a Brazilian Savanna (Cerrado) in Southern Mato Grosso

Brazilian savanna (cerrado) is composed of vegetation and soil types that are spatially variable, and links between cerrado physiognomy and soil properties are poorly understood. To reduce this uncertainty, we measured the plant community structure within cerrado vegetation types located near Cuiaba, Mato Grosso, Brazil, that varied in soil physical and chemical properties. We hypothesized that vegetation composition, including tree density, leaf area index (LAI), grass cover, and tree species diversity would be highly correlated with soil C content and fertility. Our results indicate that soil organic matter content (SOM) was significantly (p &lt; 0.05) correlated with tree density and LAI but negatively correlated with grass cover. Moreover, SOM content explained almost all of the spatial variation in cation exchange capacity (CEC) and soil N content (Pearson r &gt; 0.90), and tree species diversity and richness increased significantly with soil fertility. These data suggest that cerrado species richness and diversity is coincident with more fertile soils, which is qualitatively similar to results reported for tropical forests across regional fertility gradients in the Amazon Basin. These results have implications for the maintenance of soil C storage and fertility and tree species diversity in cerrado.

Soil Profile Characteristics As Affected By Land Use Systems In The Southeastern Adamawa State, Nigeria

The success of soil management to maintain soil quality depends on an understanding of how soils respond to agricultural use and practices over time. As a result, the important soil quality indicators were assessed under different land use systems to provide base line data for future research in Southeastern Adamawa State, Nigeria. The different land use systems were the cultivated land, natural fallow land, Gmelina plantation, pasture and the undisturbed natural forest land. One soil profile was opened in each land use system for field descriptions and laboratory studies in 2012/2013. The soil physical properties such as structure, colour, particle size distribution and soil depth characteristics showed notable variations due to different land use system, particularly in the surface horizons. The soil textures ranged from clay loam in the cultivated land, pasture land, undisturbed natural forest to sandy clay in the Gmelina plantation and sandy clay loam in the natural fallow land. The soil pH measured in water of the cultivated land, pasture, undisturbed natural forest and natural fallow lands varied from moderately acid to slightly acid in the Gmelina plantation. The OC and the total N decreased consistently from the surface to the subsurface horizons in all the land use systems. The surface horizons of the undisturbed natural forest, Gmelina plantation and the pasture land recorded the highest amount of OC/TN compared to the cultivated and natural fallow lands. This implies that intensive cultivation significantly deplete OC and TN. There was great variation in cation exchange capacity (CEC) of the soils under the different land use systems both in the upper and subsurface soil horizons. The CEC decreased almost inconsistently from the surface to the subsurface horizons in all the different land use systems. The decrease in CEC with depth could be attributed to a decrease in organic matter content with soil depth. Therefore, the depletion of organic matter as a result of intensive cultivation has reduced the CEC under the natural fallow and cultivated lands surface horizons respectively.

Development of organovermiculite-based adsorbent for removing anionic dye from aqueous solution

This paper reports on the development of organovermiculite-based adsorbent for removing Congo Red (CR), a model anionic dye, from aqueous solution. The organovermiculite was prepared using hexadecyl trimethylammonium bromide (HDTMAB) with variations in cation exchange capacity (CEC) and was then characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results from the adsorption experiments showed that with the organic modification of 50, 100, and 200% CEC, the adsorption capacity of vermiculite towards CR was greatly improved from 2.6 to 74.07, 175.44 and 192.31 mg/g, respectively, at 298 K. The adsorption isotherm experiment was conducted at different temperatures (298, 308 and 318 K), and it was found that the uptake of CR increased with increasing temperature. Langmuir and Freundlich isotherm models were applied and the Langmuir model was found to fit the equilibrium data better. The adsorption kinetics was found to follow the pseudo-second-order model. In addition, various thermodynamic parameters such as changes in enthalpy, entropy, and the Gibbs free energy were calculated, showing adsorption to be an endothermic yet spontaneous process. The results indicated that the organovermiculite may be an effective adsorbent for the removal of anionic dyes from wastewater.

Variations in the cation exchange capacity of a ferralsol supplied with vinasse, under changing aeration conditions: Comparison between CEC measuring methods

The spreading of vinasse may favour soil anoxia and affect cation exchange capacity (CEC). Our aims were to assess the reliability of CEC measurements in reducing conditions, quantify CEC variations in a ferralsol under changing aeration conditions, and understand the mechanisms involved. In a first experiment, soil slurry was incubated for a succession of 7 oxic, 28 anoxic and 28 oxic days, vinasse being supplied when anoxia began. CEC was measured at intervals by exchanging Mg 2+, Cu-trien or Co(NH 3) 6 3+, the solutions being characterized before and after exchange. In a second experiment, soil CEC was measured after the elution of NH 4 + solutions of pH 5 to 7. In a third experiment, we assessed the reduction of Co(NH 3) 6 3+ by Fe 2+ and checked for induced changes by geochemical simulations. During the first oxic period, CEC varied according to method, in the order: Cu-trien < Mg2 +<Co(NH 3) 6 3+<NH 4 +. It increased by 2 cmol c kg − 1 when pH increased from 5 to 7. After 28 days of anoxia, CEC estimates were 2.75, 1.43 and 5.1 times their initial values for the 0.05 M Mg 2+, Cu-trien and Co(NH 3) 6 3+ methods respectively; pH after exchange was about the same as initial slurry pH (6.9), except after Co(NH 3) 6 3+ exchange when it was 9.4. This complex was partly reduced by Fe 2+ leading to NH 3 release, pH increase, Fe(OH) 3 and Co(OH) 2 precipitations, Co(II) adsorption and overestimation of CEC. After the return to oxic conditions, the CEC did not return to its initial value. At all dates, CEC measured by 0.05 M Mg 2+ method agreed with the exchangeable cation measurements.

Prediction of cation exchange capacity from soil index properties

AbstractIn many areas of geotechnical engineering it is necessary to have an estimate of the cation exchange capacity (CEC) of a soil in order to allow preliminary design estimates. Standard methods of CEC determination are time-consuming and involve several steps (e.g. displacement of the saturating cation requires several washings with alcohol). Therefore, a rapid method of CEC estimation would be very useful. During preliminary site investigations, the soil engineering parameters can be estimated from the considerable number of correlations available in the literature. In this study, relationships between CEC and various other soil engineering properties have been investigated, resulting in a quick method for estimating CEC.Simple correlations were developed between CEC and specific surface area (SSA), soil organic matter (OM), clay fraction (CF), activity (A), Atterberg limits (liquid (LL), plastic (PL), and shrinkage (SL)), and modified free swell index (MFSI) of the soils. Strong correlations are observed between the CEC values and those for ethylene glycol monoethyl ether (EGME) uptake and methylene blue (MB) titration. However, no significant correlation was found between CEC and N2_SSA. No unique relationship was seen between CEC and CF (r2 &lt;0.5). No relationship was observed between CEC and OM in this study. The best correlation coefficient between the CEC and Atterberg limits exists between CEC and LL (r2 = 0.61). No significant relationship was seen between CEC and PL or SL. The correlation coefficient between CEC and MFSI was 0.65. Multiple linear regression analyses were developed to investigate the contributions of different soil parameters to CEC. These analyses show that EGME_SSA, in combination with LL, accounted for 91% of the variation in CEC. Correlations between CEC and EGME_SSA, MB_SSA and LL appear to be sufficiently good to enable an indication of CEC to be estimated from these parameters.

Relative sensitivity of ESP profile to spatial and temporal variability in cation exchange capacity and pore water velocity under simulated field conditions

To assess the effects of spatial variability in soil properties and temporal variability in irrigation water quality, a number of simulations are carried out using an analytical and numerical model (UNSATCHEM). The scaling theory is used for the variability of hydraulic conductivity, and thus for the variability of flow. Monte Carlo simulations are also carried out to investigate the effect of spatial variability of cation exchange capacity on exchangeable sodium percentage (ESP) profile. Field data, published for the semi arid Hisar region in the Haryana State of India, indicate that the cation exchange capacity ( Q) and the pore water velocity ( v ) are log normally distributed. Randomly generated values of Q, v and joint variable Y (equal to v / Q ) are used in spatial analysis. Results reveal that spatial variation of the cation exchange capacity and pore water velocity have little effect on ESP development in topsoil, where the soil solution reaches local equilibrium with irrigation water and thus the maximum value of ESP is observed. The alternate use of alkali groundwater and canal water is the cause for temporal variability of irrigation water quality, which significantly influences the ESP-values that develop in the topsoil. The CO 2 concentration in root zone, annual rainfall, amount of fresh water available for irrigation and soil texture also affect the alkalisation. Results obtained will be helpful in finding better conjunctive use plans of alkali and canal water depending upon the irrigation water quality and crop tolerances at different growth stage.

Predicting Cation Exchange Capacity for Soil Survey Using Linear Models

Measuring the cation exchange capacity (CEC) for all horizons of every map unit component in a survey area is very time consuming and costly. The objective of this study was to develop CEC (pH 7 NH4OAc) prediction models that encompass most soils of the United States. The National Soil Survey Characterization database was used to develop the predictive models using general linear models. Data were stratified into more homogeneous groups based on the organic C content, soil pH, taxonomic family mineralogy class and CEC‐activity class, and taxonomic order. Models were developed for each strata or data group. Organic matter and noncarbonate clay contents were the main predictor variables used. Water at −1500 kPa was used in lieu of clay content on four groups. Results indicate that between 43 and 78% of the variation in CEC could be explained for the high organic C data groups; between 53 and 84% could be explained for the mineralogy groups; between 86 and 95% could be explained for the CEC‐activity class groups; and between 53 and 86% could be explained for the taxonomic orders. The same predictive model was applicable for Gelisols and Histosols. Inceptisols and Alfisols (&gt;0.3% organic C) also shared the same model. In general, the mineralogy/CEC‐activity class equations had lower RMSEs than the taxonomic order equations. A decision tree, based on how the data was stratified, guides the selection of which model to use for a soil layer. Validation results indicated that the models, in aggregate, provide a reasonable estimate of CEC for most soils of the United States.

Radial variations in cation exchange capacity and base saturation rate in the wood of pedunculate oak and European beech

In a mixed forest stand on an ochreous brown earth in the Belgian Ardennes, pedunculate oak (Quercus robur L.) and European beech (Fagus sylvatica L.) have outwardly decreasing cation concentration profiles in wood. To test if these profiles can be ascribed to endogenous factors or to decreased availability of cations in the soil, radial profiles of water-soluble, exchangeable, and total cations and of cation exchange capacity (CEC) of wood were determined. In both species, [Formula: see text]75% of K is in the water-soluble form so is of little use for dendrochemical monitoring. About 80% of Mg is adsorbed on wood exchange sites. For Ca, 30 (beech) to 60% (oak) of total content cannot be extracted by SrCl2 and is, thus, relatively immobile in wood. Wood CEC decreases from pith to bark in European beech and from pith to outer heartwood in pedunculate oak. Decreasing profiles of exchangeable Ca and Mg in pedunculate oak and exchangeable Ca in European beech are strongly constrained by CEC and, thus, are not related to environmental change. Base cation saturation rate shows no consistent radial change in either species. European beech maintained much higher base cation saturation rate than pedunculate oak, although both species had similar CEC. In conclusion, the results do not provide convincing evidence for a significant change in nutritional status of pedunculate oak and European beech in the Belgian Ardennes due to atmospheric pollution.

Pesticide retention by inorganic soil amendments

Pesticide retention by eight inorganic soil amendments, the majority of which are used in turf, was evaluated using a laboratory-based technique with radiolabeled pesticides. Amendments evaluated were derived from various naturally-occurring deposits of zeolites, diatomaceous earths, and fired clays and are intended to provide long-lived, stable, and uniformly sized particles that can contribute favorable water- and nutrient-retention properties to the root zone. Sand, sedge peat, and a Marvyn loamy sand soil (Ap horizon) were included for comparative purposes. Pesticides evaluated included the herbicides imazaquin and oxadiazon and the fungicide/herbicide fenarimol. Pesticide retention was evaluated with a soil solution technique. Amendments evaluated had considerable variation in cation exchange capacity (CEC), effective CEC (ECEC), surface area (SA), and field capacity with lesser variation in particle size distribution and particle density. Scanning electron microscopy revealed that surface texture was variable but frequently rough and porous. Pesticide retention was also variable but generally more than that of sand and frequently equivalent to sedge peat. Only with fenarimol and amendments that had been Ca+2-saturated could retention be correlated with any of the individual physical or chemical parameters that are generally assumed to govern pesticide adsorption, which in this case were CEC and SA. Imazaquin retention by unaltered amendments was correlated only with the products of SA and CEC, and SA and ECEC. Retention of both oxadiazon and fenarimol by unaltered amendments could not be correlated with any individual physical and chemical parameters or products thereof. Pesticide retention by these amendments is probably the cumulative sum of both true adsorption and physical entrapment.

Cation exchange capacity variations in acidic forest soils from Sutton, Québec, Canada

Abstract Single values of the cation exchange capacity (CEC) are widely used in modeling soil solution chemistry in soil and water ecosystems. Our aim was to determine the CEC as a function of pH and ionic strength in an acidic forest soil. We examined the cation exchange of two Humo‐Ferric Podzols (Haplorthods) equilibrated with artificial soil solutions of different concentrations. Aliquots of acid (HC1) or base (NaOH) were added to generate a pH range of 3 to 6. The CEC, determined by displacement with BaCl2 showed little or no increase with increasing pH and a definite increase with lower pH. This anomalous behavior was attributed to the precipitation of aluminum (Al) at high pH and to its dissolution at low pH.