High Cation Exchange Capacity Research Articles

Comparative Study of Organoclays with Ionic Surfactant

The clays of the smectite group, mainly montmorillonite, are widely used in the production of organoclays due to the small dimensions of the crystals, high cation exchange capacity (CEC), and swelling capacity in water, which lead to a rapid and efficient intercalation of organic compounds used in the synthesis. In this context, this research was intended to make a comparative study of clays organofilized with ionic surfactants through their respective CEC. We selected four samples of bentonites, namely Chocolate (Boa Vista, PB), Brasgel (industrial), Dark Bentonite (Pedra Lavrada, PB) and M400 Bentonite (industrial). The natural samples were characterized through XRD, EDX, TA and GA, and the organofilized ones through XRD. The characterization tests showed that the samples are composed of clay minerals of the smectite group, the CEC values ​​were insignificant changes when comparing the values ​​of natural and activated clays with sodium carbonate. And the levels indicated by the CEC for the ionic surfactant Praepagem HY proved insufficient to transform the organophilic clays, as the nominees for the ionic surfactant Praepagem WB led to adequate results regarding the incorporation of the surfactant in the clay fraction of the studied samples.

Adsorption of Nickel and Zinc by Residual Soils

Soil has long been utilized as low cost liner material to prevent contamination from leachate to groundwater media. To find a suitable soil material for this purpose is a great challenge. This study describes the potential use of residual soil to functions as engineered clay liner for waste disposal landfill in Malaysia. Three types of residual soils were investigated namely marine clays (SBMC1, SBMC2), Residual Granites (BGR, KGR) and residual meta-sediments (BBMS1, BBMS2 and PMS). Physical and chemical tests were applied for both granitic soils to determine the physical and chemical properties of soil materials. Physical and chemical tests involved grain size distribution, Atterberg limits, compaction, pH, organic content, specific gravity, Cation Exchange Capacity (CEC) and Specific Surface Area (SSA) as well as Batch Equilibrium Test for adsorption of heavy metals. The best potential soil materials for clay liner is the materials that have high pH value, high organic matter, high liquid and plastics limits, high CEC and SSA values. The best material also highly dominated with clay (in this case PKMC, SBMC1 and SBMC 2). Result show the range of pH values are from 6.95-8.36, range of organic content are from 4.35-6.41%, the specific conductivity values range from 2.13-2.34 and for liquid limit and plastic limit range are from 56.40-84 and 26.86-59.35% respectively; which is high to very high plasticity. Residual soils as low-cost adsorbent materials were also used for removal of Nickel (Ni) and Zinc (Zn) from aqueous solutions. Batch test was used and the effect of heavy metal concentration was studied. Results were analyzed using adsorption isotherm models (i.e., Linear, Langmuir and Freundlich). Based on the correlation coefficient (r2 values), most of residual soils fitted nicely to Linear, Langmuir and Freundlich models. For Ni, most soils fitted to Langmuir models except for meta-sediment while for Zn fitted to Linear model. Marine clay has the highest adsorption coefficient ranged between KL = 0.2380-0.9655

Efecto de la calidad de la materia orgánica asociada con el uso y manejo de suelos en la retención de cadmio en sistemas altoandinos de Colombia

Cadmium from soils by weathering and anthropogenic activities can have produce toxic effects associate to low affinity of adsorbents forms, high solubility and mobility. It is very important to conduct studies leading to knowledge of adsorption phenomena and cadmium mobility factors and predict possible toxici-ty in High Andeansoils whose use is changing to pastures and crops with applications of phosphate fertilizer with presence of Cd in composition. High Andean soils subbasin Rio Las Piedras, (Department of Cauca), with systems of forest, crop and pasture were characterized by physical and chemical properties, highlighting strong acidity, presence of allophones, high in organic carbon, high cation exchange capacity, low density of soil. The quality of soil organic matter was assessed by different humification index obtained with the different fractions characterized to determine the influence on cadmium retention phe-nomenon and mobility factor. The retention was evaluated by Freundlich adsorption isotherms in humic acids and soils of the three systems. The K (maximum adsorption capacity) and n (retention force) values correspond to 131. 98 and 1.18 in forest soils, 340.93 and 1.19 for crop, 170.36 and 1.19 in pasture, and are lower than those of humic acids in the three systems. The quality of the organic matter has a significantly effect on these processes, better quality results in less mobility preventing groundwater contamination and bioaccumulation toxicity.

Oxygen isotope fractionation effects in soil water via interaction with cations (Mg, Ca, K, Na) adsorbed to phyllosilicate clay minerals

Summary In isotope-enabled hydrology, soil and vadose zone sediments have been generally considered to be isotopically inert with respect to the water they host. This is inconsistent with knowledge that clay particles possessing an electronegative surface charge and resulting cation exchange capacity (CEC) interact with a wide range of solutes which, in the absence of clays, have been shown to exhibit δ 18 O isotope effects that vary in relation to the ionic strength of the solutions. To investigate the isotope effects caused by high CEC clays in mineral–water systems, we created a series of monominerallic-water mixtures at gravimetric water contents ranging from 5% to 32%, consisting of pure deionized water of known isotopic composition with homoionic (Mg, Ca, Na, K) montmorillonite. Similar mixtures were also created with quartz to determine the isotope effect of non-, or very minimally-, charged mineral surfaces. The δ 18 O value of the water in these monominerallic soil analogs was then measured by isotope ratio mass spectrometry (IRMS) after direct headspace CO 2 equilibration. Mg- and Ca-exchanged homoionic montmorillonite depleted measured δ 18 O values up to 1.55‰ relative to pure water at 5% water content, declining to 0.49‰ depletion at 30% water content. K-montmorillonite enriched measured δ 18 O values up to 0.86‰ at 5% water content, declining to 0.11‰ enrichment at 30% water. Na-montmorillonite produces no measureable isotope effect. The isotope effects observed in these experiments may be present in natural, high-clay soils and sediments. These findings have relevance to the interpretation of results of direct CO 2 -water equilibration approaches to the measurement of the δ 18 O value of soil water. The adsorbed cation isotope effect may bear consideration in studies of pedogenic carbonate, plant-soil water use and soil-atmosphere interaction. Finally, the observed isotope effects may prove useful as molecular scale probes of the nature of mineral–water interactions.

Sorption and desorption of tetracycline on layered manganese dioxide birnessite

Birnessite is one of the most common manganese oxides in the clay-sized fraction (<2 μm) of soils and has high cation exchange capacity and larger surface area. Birnessite was previously studied for decomposition of selected antibiotics from water. In this study, the removal of tetracycline (TC) by birnessite from aqueous solution was investigated as a function of initial tetracycline concentration, solution pH, temperature, and equilibrium time. Changes in solid phase after TC adsorption and desorption were characterized by X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and Fourier transform infrared analyses. Desorption of exchangeable cations accompanying TC removal and partial desorption of TC from birnessite by AlCl3 confirmed that cation exchange was responsible for TC removal at low initial concentrations. Both the external and internal surface areas were readily available for TC uptake by birnessite. The intercalated TC formed a horizontal monolayer configuration in the interlayer of birnessite as deduced from XRD analyses.

Nanostructured Gold-Nickel/Titania Nanotubes Electrocatalysts for Hydrazine Oxidation

This work is focused on the study of self-ordered titania nanotube arrayed electrodes for preparation of efficient nanostructured gold-nickel/titania nanotubes (denoted as Au(Ni)/TiO2-NTs) electrocatalysts for the oxidation of hydrazine in alkaline medium. Titania nanotube arrayed substrate was applied for preparation of catalysts due to its high cation exchange capacity, which provides the possibility of achieving a high loading of active catalyst with an even distribution and high dispersion. The self-ordered TiO2 nanotube arrays were prepared by anodic oxidation of Ti surface in an aqueous sulfuric acid solution containing some NH4F. The average tube diameter was ~100 nm and the thickness of titania layers was ~350 nm. Gold nanoparticles in size of ~10-30 nm were deposited on the surfaces of titania nanotube arrays by partial galvanic displacement of electroless nickel layer that had been previously deposited. The electroless Ni-P layer with the thickness of ~300 nm was deposited on the titania nanotubes surface, which produces a layer of granular nickel particles ~200 nm in size.The morphology, structure and composition of the prepared nanostructured catalysts were examined by field emission scanning electron microscopy, energy dispersive X-ray analysis and inductively coupled optical emission spectroscopy. The electrocatalytic activity of the prepared catalysts was investigated towards the oxidation of hydrazine in alkaline medium by means of cyclic voltammetry and chronoamperometry.Data on the pecularities of various electrodes are compared and discussed on the basis of electrochemical data. The prepared Au(Ni)/TiO2-NTs catalysts with different Au loadings possesses a higher electrocatalytic activity towards the oxidation of hydrazine in alkaline medium as compared to that of TiO2-NTs and Au deposited electrochemically on the TiO2-NTs and seem to be a promising anode materials for direct hydrazine fuel cells. Acknowledgment J. Rakauskas acknowledges support by project "Promotion of Student Scientific Activities" (VP1-3.1-ŠMM-01-V-02-003) from the Research Council of Lithuania. This project is funded by the Republic of Lithuania and European Social Fund under the 2007-2013 Human Resources Development Operational Programme’s priority 3.

안산천에서 이탈리안 라이그라스 혼파조합이 사초생산성과 토양 특성에 미치는 영향

This experiment was carried out to order to determine the forage production and soil characteristics in mixtures of Italian ryegrass (IRG) and annual legumes at the riverbed. The IRG and hairy vetch mixture had the highest in fresh, dry matter (DM) as well as total digestible nutrients (TDN) yields among the forage mixtures. Further IRG and hairy vetch mixture had the highest in DM content. The crude protein (CP) content of IRG and hairy vetch mixture was the highest, Whereas non-fiber carbohydrate (NFC) and TDN contents were lower compared to other mixtures. The total nitrogen (TN) of IRG and hairy vetch mixture was the highest due to high nitrogen fixation in the riverbed soil. The IRG and rape mixture was the highest in organic matter (OM) of soil. Moreover, the available P2O5 of soil in IRG and crimson clover mixtures was higher compared to other mixtures. Further, the IRG and hairy vetch mixture was the highest in cation exchange capacity (CEC) content. Therefore IRG and hairy vetch mixture is more suitable in forage mixtures due to high forage production and protein as well as high soil CEC content at the riverbed. (

Antibacterial activity of the soil‐bound antimicrobials oxytetracycline and ofloxacin

Soil contamination of antimicrobials has become an increasing concern because of the potential risks to the soil microbial ecosystem and human health. The present study investigated sorption and desorption behaviors of oxytetracycline (OTC) and ofloxacin (OFL) in 3 typical soils (A, B, and C), and evaluated the antibacterial activity of soil-adsorbed compounds to a pure sensitive strain Escherichia coli ATCC 25922. The results showed different sorption and desorption behaviors of OTC and OFL in the 3 soils, behaviors that were mainly influenced by soil organic matter content and cation exchange capacity (CEC) as well as pH value. In addition, complexation and cation-exchange reactions were shown to be the main sorption mechanisms. Strong adsorption was found in soil B (with a high organic matter content) and in soil C (with high CEC), whereas enhanced desorption was observed in soil A (with low organic matter content). The results also demonstrated that soil-bound antimicrobials retained antibacterial activity toward E. coli. Opposite patterns of antibacterial activity were found for the 2 antimicrobials in the 3 soils: A>B>C for OFL; and C>B>A for OTC. This finding suggests that soil-bound antimicrobials could still exert selective pressure on soil bacteria although less effectively in comparison with the dissolved forms.

Surface Properties of Petrologic End-Members from Alberta Oil Sands and Their Relationship with Mineralogical and Chemical Composition

Clays cause problems in all crucial stages of bitumen extraction, and they affect bitumen recovery and waste management. It is thus of great importance to understand the mineralogy, chemistry, and surface properties of clays to improve both bitumen recovery and tailings treatment. Four petrologically different types of Alberta oil sands ores—called “end-members”—were examined in this study by cation exchange capacity (CEC), specific surface area (SSA), total specific surface area (TSSA), and negative layer charge density (LCD) measurements in order to better understand the effects of clay surface properties on bitumen nonaqueous extraction and solvent recovery from the extraction tailings. The surface properties are primarily controlled by the mineralogy of the petrologic end-members, mainly by the type and quantity of clay minerals. CEC, SSA, TSSA, and LCD increased as the amount of 2:1 clays (illite and illite–smectite), in particular expandable interstratified illite–smectite, increased. CEC values increased with increasing SSA and TSSA. The number of H-aggregates increased and the number of monomers decreased in the second derivative spectra of Rhodamine 6G and Methylene Blue as the 2:1 clays content in the petrologic end-members increased. This indicated a greater negative layer charge density with an increasing amount of 2:1 clays. The molecular aggregation of the organic dyes (Rhodamine 6G and Methylene Blue) was observed in the second derivative spectra for petrologic end-members bearing >25 wt % of 2:1 clays. Overall, the results indicate that interstratified illite–smectite may be largely responsible for high CEC, SSA, TSSA, and LCD in the fine size fractions of petrologic end-members from Alberta oil sands.

Ability of natural, acid-activated, and surfactant-modified Terra Rossa soils to sorb triazine herbicides and their degradation products

Two Terra Rossa soils that were collected in the Mediterranean region of Croatia and Turkey were tested in their natural, acid-activated, and surfactant-modified forms as sorbents for hydrophobic triazine groundwater pollutants in terms of their potential application to the multi-mineral landfill barriers. The soils were predominantly composed of kaolinite, followed by quartz, calcite, iron-bearing oxides/oxyhydroxides, and several other types of clay. The natural soils were poor in organic carbon (OC ≤2%), were similar in chemical composition, and were significantly different in their cation-exchange capacity (CEC). Sorption experiments were conducted with hydrophobic, weakly basic and ionisable triazine herbicides (atratone, ametryn, and atrazine) and three atrazine dealkylated degradation products. The Freundlich sorption parameters were evaluated and compared with respect to the physicochemical properties of the sorbates and sorbents. The low affinities of the natural soils for the sorption of all of the tested triazines were significantly enhanced by soil acid activation. The highest fractions of sorbed triazines were observed in the acid-activated soil with the higher CEC: 90% for the most basic and partially protonated atratone and ametryn and 78% and 61% for the more polar degradation products deisopropylatrazine and didealkylated atrazine, respectively. The enrichment of natural soils with OC by the sorption of the cationic surfactant hexadecyltrimethylammonium bromide (HDTMA) was more efficient in soil with higher CEC. The sorption intensities of all of the triazines except the most polar didealkylated atrazine increased significantly with increasing soil OC and correlated positively with the hydrophobicity of the compound. The sorption capacities of the HDTMA-modified soils were greater for most compounds than the capacities of the acid-activated soils. Based on the calculated sorbate fractions that were resistant to desorption, atratone and ametryn would be expected to be retained longest in the acid-activated soils, while the soil modification with HDTMA primarily prolonged the retention of ametryn and atrazine. The results indicated that, unlike natural Terra Rossa soils, their acid-activated or surfactant-modified forms could be applicable as components of an organophilic layer in multi-mineral barriers for retention of triazines and similar chemicals.

Study on the Effect of Adding Zeolite and other Bio-Adsorbance in Enhancing the Quality of the Palm Based Vermicompost

This research work deals with the production of vermicompost from empty fruit bunch (EFB) blended with cow dung using an epigeic earthworm known as Eudrilus Eugeniae. The vermicomposting mixture was carried out in a humid environment with moisture content between 70% to 80% and a pH of between 6 to 8. Natural zeolite, such as clinoptilolite and charcoal were mixed with vermicompost at different ratios and prior to being pelletized. The highest cation exchange capacity (CEC) was observed at 10% of zeolite (Z2) and 20% of charcoal (C4) mixtures. The proportion of 10% zeolite in the mixture resulted in the highest of Cu reduction by 44% and manganese by 60% and in addition the 15% charcoal caused the highest reduction of iron (Fe) by 32%. A significant decrease in carbon to nitrogen C/N ratio and an overall increase in total nitrogen, total available phosporous and total potassium were also discussed in this paper.

Effect of sowing dates, seed rates and integrated nutrition on productivity, profitability and nutrient uptake of summer mungbean in Eastern Himalaya

A field experiment was carried out in the summer seasons of 2010–2012 at north eastern hilly region of Jharnapani, India, to evaluate the effect of sowing dates, seed rates and integrated nutrition on productivity, profitability and nutrient uptake of summer mungbean. Experimental results revealed that 5th April sown crop recorded significantly higher growth attributes, yield, and economics than 15th April sown crop. This was mainly because of the fact that almost all the yield attributing characters were favourably influenced because of early sowing and, therefore, yield increased. Similarly, 5th April sown crop resulted in higher cation exchange capacity (CEC) of roots, root N content, nitrogenase activity (NA), total uptake of N, P, K and protein yield than the 15th April sown crop. Higher yield and economics were found with seed rates of 35 kg ha−1, whereas CEC of roots, root N content and NA were higher at 20 kg ha−1. Application of 50% RDF (recommended dose of fertilizer) + 50% RDN (recommended dose of nitrogen as vermicompost) + PSB (phosphate solubilizing bacteria) produced significantly higher growth attributes, yield and economics of mungbean.

Evaluating the potential of sediments in Ziqlab Reservoir (northwest Jordan) for soil replacement and amendment

Surface sediments of Ziqlab Reservoir, northwest Jordan, were evaluated to characterize trace element distributions and sources related to various physicochemical variables. Trace element distribution is determined by texture, parent material in the catchment, and anthropogenic activities. The suitability of reservoir sediment for replacing or amending soil was assessed by comparing sediment characteristics to natural soils. Results suggest that the sandy facies can be used as artificial soils, whereas clayey facies can be utilized as fertilizer for poor quality soils in Jordan. The fine-grained sediment fraction is associated with (1) high abundance of clay minerals with high cation exchange capacity and available micronutrients; (2) occurrence of kaolinite, montmorillonite–illite, vermiculite, and smectite; and (3) optimal pH values for availability of most micronutrients. Among the trace elements measured, total nickel and cadmium slightly exceeded recommended safe levels for soils, but the high concentrations may decline when sediments are exposed to air. If removal of the bottom sediments of Ziqlab Reservoir becomes economically feasible, it would extend the reservoir lifespan, improve water quality, compensate for soil scarcity in some regions, and enhance soil productivity.

Response of Rice and Carbon Emission to Application of Ameliorant Dregs in The Peat Soil with Saturation and Unsaturation Condition

Fertility of peat land is very poor and makes it not suitable for crop without any high input. This condition was indicated by the very high soil acidity ( low pH), low availability of macro (N, K, Ca and P), and micro (Cu, Zn, Mn and Bo) nutriens and high cation exchange capacity (CEC) but low base saturation (BS), the presence of toxic organic acid. The main organic acids, as a result of lignin biodegradation and the sources of C-release, are of aromatic group consisting mainly of derivate phenolic acids. The peat soil material was taken at depths from 0 to 30 cm, with weathering rate saprik and dregs from Indah Kiat Pulp and Paper at Perawang, Riau. These experiments using split plot design, the main plot is the condition of the water (unsaturated and saturated) and the subplot is ameliorant dregs consisting of 4 levels (0, 10, 15 and 20 ton ha -1 ), each combination was repeated 4 times. The activities were focused on the interaction of water condition and ameliorant dregs, and its influences to growth and yield of rice, C-emission (CO 2 and CH 4 ). The results showed that the aplication of dregs improves plant growth and increase the yield of rice (weight of dry milled grain) compared without dreg both at unsaturated condition and saturated conditions. The Cabon-release in the forms of CO 2 and CH 4 fluxes in saturated conditions is smaller than unsaturated conditions. The application dreg 10 t ha -1 increase the number of productive tillers and the weight of milled rice about 35 and 75% compared without dreg on saturated condition, whereas the increase is greater unsaturated conditions about 63 and 80%. The application of dregs 10 t ha -1 in saturated condition can reduce CO 2 and CH 4 emissions about 18.19% and 93.71% compared without dreg, otherwise the application dreg 10-20 t ha -1 increase the production of CO 2 and CH 4 in unsaturated conditions.

分子間力を考慮したモンモリロナイトの膨潤モデルの構築

本研究では陽イオンによるモンモリロナイト（Mo）の膨潤モデルの構築を行った。Moの体積変化は（1）Moの基本構造の単位層の集合体であるTactoid（Ta）の膨潤による体積変化と、（2）Taが形成する粗大構造の膨潤による体積変化の総和と考えた。前者は2平板の分子間力を考慮したモデルより算出し、後者の粗大構造の変化は実測した体積変化とTaの膨張による体積変化の差から算出した。粗大構造中の溶液とTa中の単位層間の溶液は一様であると考え、その化学ポテンシャルを2平板間の分子間力により決定した。その結果、粗大構造と化学ポテンシャルにはイオン種によらず関係性が見られ、化学ポテンシャルに基づくMoの膨潤予測モデルの構築ができた。

Characterization of a Sorbent Derived from Construction and Demolition Waste

Construction and demolition waste (C&amp;D) was employed as a raw material to synthesize sorbent by fusion-hydrothermal process in order to effectively use this type of waste material. The specific surface area and the cation exchange capacity (CEC) values of the sorbent were 308.2 m2 g-1 and 625.6 mmol/100 g-1, respectively. It was found that the sorbent was quite effective for ammonium ion due to the high CEC value. The sorbent possessed high PFOS sorption capacities after load with cationic surfactant (Cetyltrimethyl Ammonium Bromide, CTAB), the sorption capacities of CTAB-modified sorbents enhanced with the increase of CTAB loading amount. This study provides an effective way for the C&amp;D waste utilization.

Biodegradation and adsorption of crude oil hydrocarbons supported on “homoionic” montmorillonite clay minerals

The role of “homoionic” montmorillonites in hydrocarbon removal during biodegradation was investigated in aqueous clay/oil microcosm experiments with a hydrocarbon degrading microorganism community. The clay mineral used for this study was montmorillonite which was treated with the corresponding metal chloride salt to produce Na-, K-, Mg-, Ca-, Zn-, Al-, Cr-, and Fe-montmorillonites used in this study. The study indicated that Zn- and K-montmorillonites were inhibitory to biodegradation of the crude oil hydrocarbons and appears to do so as a result of extensive adsorption of the hydrocarbons. However, Na-, Ca- and Fe-montmorillonites with relatively high surface area and cation exchange capacity (CEC) were stimulatory to biodegradation of the crude oil hydrocarbons. This study reveals that whereas surface area and the ‘local bridging effect’ were important factors from the clay minerals that conferred stimulatory effect on the biodegradation of the hydrocarbons, the hydrolysis of the interlayer water by trivalent cations of the clay to generate protons and increase acidity of the medium is suggested to be inhibitory to biodegradation of the crude oil hydrocarbons. The interlayer cations (trivalent cations) that impart the highest local bridging effect which is stimulatory to biodegradation also impart the highest hydrolysis of interlayer water which is inhibitory. This study showed that interlayer cations play a crucial role on the ability of the clay mineral to influence biodegradation of the hydrocarbons.

Nonlinearity of Cationic Aromatic Amine Sorption to Aluminosilicates and Soils: Role of Intermolecular Cation−π Interactions

Through the study of substituted anilines and benzylamines, we demonstrated that cooperative cation-π, π-π, and van der Waals interactions can increase aromatic cationic amine sorption to Na/Ca-montmorillonite well beyond the extent expected by cation exchange alone. Cationic amines exhibiting cooperative interactions displayed nonlinear S-shaped isotherms and increased affinity for the sorbent at low surface coverage; parallel cation exchange and cooperative interactions were noted above a sorption threshold of 0.3-2.3% of exchange sites occupied. Our experiments revealed the predominance of intermolecular cation-π interactions, which occurred between the π system of a compound retained on the surface via cation exchange and the cationic amine group of an adjacent molecule. Compounds with greater amine charge/area and electron-donating substituents that allowed for greater electron density at the center of the aromatic ring showed a greater potential for cation-π interactions on montmorillonite surfaces. However, benzylamine sorption to nine soils, at charge loadings comparable to the experiments with montmorillonite, revealed no significant cooperative interactions. It appears that cation-π interactions may be likely in soils with exceptionally high cation exchange capacities (>0.7 mol charge/kg) and low organic matter contents, abundant in montmorillonite and other expanding clay minerals.

English

Sub-adult earthworms, Eudrilus, Eugenae were cultured for 100 days in rubber containers made from old tyres to determine the plant nutrient release composition in vermicompost using different organic diets. The diets are Andropogon grass + Pig manure (AGPM) Andropogon grass (AG), Bracharia grass + pig manure (BGPM) and Bracharia grass (BG). Result of the study show that the produced vermicompost in each diet consisted mostly of high quality humus with favorable pH level and high cat ion exchange capacity (CEC) which varied with the diets. Pig manure enhanced the CEC of the vermicompost by 114.82%. Available P, exchangeable Ca and Mg were significantly (p = 0.05) increased in the vermicompost and varied among the various diet treatments. Available P was greatest with Andropogon vermicompost relative to the Bracharia vermicompost. Pig manure enhanced the release of available P of Andropogon vermicompost by over 185% and over 1000% in Bracharia vermicompost relative to the grass vermicompost alone. Exchangeable Ca and Mg of Bracharia vermicompost was enhanced 32 and 74% respectively by Pig manure. Results of the study also show increase in earthworm biomass production and cocoon size in the vermicompost which varied among the diet treatments and non-significant difference among the vermicompost in water holding capacity. Weight loss from composition and decomposition rate was highest in BG relative to BGPM, AG and AGPM. Average decomposition rate of the grass diet was 75.25%. Earthworm (Eudrilus eugenae) through its activities increased the rate of decomposition and degradation of organic wastes and is effective in plant nutrient release if subjected to proper culturing with suitable feed materials. Key words: Eudrilus eugenae, vermicompost, Brancharia grass, Andropogon grass.

High exchangeable calcium concentrations in soils on Barro Colorado Island, Panama

The soils on four lithologies (basaltic conglomerates, Bohio; Andesite; volcanoclastic sediments with basaltic agglomerates, Caimito volcanic; foraminiferal limestone, Caimito marine) on Barro Colorado Island (BCI) have high exchangeable Ca concentrations and cation-exchange capacities (CEC) compared to other tropical soils on similar parent material. In the 0–10cm layer of 24 mineral soils, pH values ranged from 5.7 (Caimito volcanic and Andesite) to 6.5 (Caimito marine), concentrations of exchangeable Ca from 134mmolckg−1 (Caimito volcanic) to 585mmolckg−1 (Caimito marine), and cation exchange capacities from 317mmolckg−1 (Caimito volcanic) to 933mmolckg−1 (Caimito marine). X-ray diffractometry of the fraction <2μm revealed that smectites dominated the clay mineral assemblage in soil except on Caimito volcanic, where kaolinite was the dominant clay mineral. Exchangeable Ca concentrations decreased with increasing soil depth except on Caimito marine. The weathering indices Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA) and Weathering Index of Parker (WIP) determined for five soils on all geological formations, suggested that in contrast to expectation the topsoil (0–10cm) appeared to be the least and the subsoil (50–70cm) and saprolite (isomorphically weathered rock in the soil matrix) the most weathered. Additionally, the weathering indices indicated depletion of base cations and enrichment of Al-(hydr)oxides throughout the soil profile. Tree species did not have an effect on soil properties. Impeded leaching and the related occurrence of overland flow seem to be important in determining clay mineralogy. Our results suggest that (i) edaphic conditions favor the formation of smectites on most lithologies resulting in high CEC and thus high retention capacity for Ca and (ii) that there is an external source such as dust or sea spray deposition supplying Ca to the soils.