Joseph Dufey

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.

Adsorption and exchange of Ca, Mg and K-ions on the root cell walls of clover and rye-grass

SummaryThe ion exchange properties of clover and rye-grass root cell walls were studied quantitatively. Three sets of experiments were performed: adsorption of Ca, Mg and K ions versus pH, adsorption versus cation concentration and exchange isotherms Ca−Mg and Mg−K. A model has been developed. It allows the satisfactory prediction of results (except for pH curves) with the adjustment of a minimum of parameters. The total charge (RT), on its own, accounts for the difference between the ion exchange properties of the clover and rye grass cell walls. The selectivities observed on root material are very different from those observed on soil exchange complexes. The decreasing affinities of cell walls for cations follow the sequence: Ca>Mg≫K for cell walls. These differences of selectivity are much larger than those usually observed for soil exchange complexes.

Potassium exchange behaviour in Carribean volcanic ash soils under banana cultivation

Ca−K exchange isotherms of samples from carribean (Martinique island) volcanic soils differing in the weathering stage and in the nature of cation-exchange material were studied. Allophanic soils high in organic matter (Troporthents, Hydrandepts) exhibit a low selectivity for K-ions. Potassium is adsorbed specifically in the halloysitic soils (Humitropepts). A positive relationship exists between the affinity for K+ and the halloysite content. This relation is most likely due to the close association of 1∶1 hydrated phyllosilicates with 2∶1 smectitic clay minerals. A lower selectivity for K was observed in the kaolinitic soil materials (Dystropepts). Because parent rocks are very low in K, these exchange properties strongly influence their K status, through differences in susceptibility to K leaching losses and K availability to banana plants in intensive cropping systems.

Model for the Electrolytic Environment and Electrostatic Properties of Biomembranes

Physical and chemical interactions of ions with biomembranes are described by a model originating from the Stern theory. Equations of the model have analytical solutions only for very simple, often unrealistic situations. The numerical resolution adopted permits a much wider application of the model: Potentials and concentrations can be calculated anywhere from the surface and in any electrolytic environment. The model is applied to biomembranes. Simulations are presented in three-dimensional figures which allow one to use the model as a practical research tool. In particular, the simulations reveal that, in practice, it is possible to induce an increase of the surface charge density simultaneously with a decrease of the surface potential, and, theoretically, that the potential at the exclusion distance (which estimates the diffuse layer thickness) exhibits a remarkably constant value as the composition of the free solution is varied.

Fertilization Capacity of Aquatic Plants Used as Soil Amendments in the Coastal Sandy Area of Central Vietnam

In Central Vietnam, and more especially in Thua Thien Hue Province, aquatic plants are used empirically by some farmers as an external source of organic matter to improve fertility of sandy soils. The fertilization capacities of aquatic plant species [Najas indica (Willid.) Cham., Najas minor All., Vallisneria spiralis L. (Michx.) Torr., Hydrilla verticillata (L.f.) Royle, Potamogetum malaianus Miq., Myriophyllum spicatum L., Enteromorpha flexuosa (Wulfen) J. Agardh, Rhizoclonium kerneri Stockmayer, and Eichhornia crassipes (Mart) Solms] were assessed from a pot trial including soils amended with aquatic plants (5 g dry matter kg−1 soil) and soils supplied with increasing rates of urea nitrogen (N) fertilizers. Rice (Oryza sativa L.) at a vegetative stage was used as a convenient bio‐extractor. The fertilization capacity of aquatic plant amendments was calculated from aboveground biomass and from N accumulated in shoots as compared to treatments receiving only inorganic N fertilizers. Najas indica (Willid.) Cham. and Hydrilla verticillata (L.f.) Royle showed the greatest fertilization capacity, equivalent to 170–180 mg urea‐N kg−1 soil as estimated from biomass yield, whereas a lesser fertilization capacity, equivalent to less than 100 mg urea‐N kg−1 soil, was observed for Myriophyllum spicatum L., Enteromorpha flexuosa (Wulfen) J. Agardh, Rhizoclonium kerneri Stockmayer, and Eichhornia crassipes (Mart) Solms. This study provides quantitative data on the fertilization capacity of aquatic plants found in the coastal area of central Vietnam, which can improve this empirical practice and alleviate local agro‐environmental constraints related to the lack of organic matter in farming systems.

Self-diffusion of sodium on clay surfaces as influenced by two other alkali cations

Abstract The surface self-diffusion of sodium was studied in mixed NaLi and NaRb-clay suspensions. The Rb + ions were found to increase the surface mobility of sodium while the Li + ions produced a very light opposite effect. This was attributed to a modification of the relative distribution of the Na + ions between the Stern and Gouy layers when another cation was introduced on the clay surface.

Selfdiffusion of anions in clay gels

Abstract Selfdiffusion studies of iodide in clay gels have shown that the effect of decreasing the anion “exclusion volume” by increasing electrolyte concentration was more than offset by an ensuing tactoid formation which occurred in a way that increased the path of the diffusing anions. This effect is more pronounced when the solid content of the gel is higher.

Downward Effects of Dolomite and Kieserite On two Acid Soils Differing in Their Organic carbon Content

Mg application proved to be a valuable tool for the revitilization and restabilization of declining forest ecosystems growing on acid soils. Adequate fertilization however still requires clear understanding of the downward effects associated with Mg-fertilizers. To that purpose, leaching experiments with Mg solutions were performed in laboratory columns filled with two types of acid soil materials differing largely by their organic carbon content : 80.2 g C kg-1 for soil A and 8.1 g C kg-1 for soil B. Magnesium was supplied either as a solution saturated in dolomite or as a pulse of kieserite solution. The columns were dismantled for analysis after 8, 16, 24, and 32 d. leaching. Dolomite increased soil pH and diminished exchangeable Al in both substrates. Substantial increase of electrical charge was noticed only in substrate A. Consequently Ca and Mg reloading in substrate B was mainly due to ion exchange with Al, whereas in substrate A the major part of the increase in exchangeable Ca and Mg was due to enhanced organic charge. Kieserite induced very little changes in soil pH and all modifications in the composition of exchange sites were achieved after the passage of the sulfate peak. In the A substrate, the increase of Mg loading resulted from an exchange process with Ca, whereas it was achieved at the expense of exchangeable Al in the B substrate. Calcium and Mg losses from the soil columns after 32 d were greater with kieserite than with dolomite. These losses were also larger for the hemiorganic A substrate than for the mineral B substrate. These results imply that both the charge characteristics of the substrate (variable or fixed) together with the kind of Mg-fertilizer are essential to consider in fertilization programmes.

Potassium buffering capacity of sandy soils from Thua Thien Hue Province, Central Vietnam, as related to soil properties

Most agricultural production in central Vietnam relies on sandy soils distributed along the sea coast. Because of their low exchangeable potassium (K) and low cation exchange capacity (CEC), careful adjustment of K fertilization on these soils is needed to minimize K leaching. Quantity/intensity curves were established on 24 sandy soils from Thua Thien Hue Province from which K buffering capacity (PBC) was calculated and compared with basic soil properties. Potassium buffering capacity was found to correlate best with soil texture and only a little with humus content, although these two characteristics are responsible for CEC. A simple equation based on sand content, which is easier to determine than clay content, is proposed to calculate optimum exchangeable K level as a function of target K level in soil solution.

Zinc Sorption in Sandy Soils from Central Vietnam as a Function of Soil Characteristics

Zinc (Zn) sorption curves were established for 11 cultivated sandy soils from central Vietnam. Soil samples (10 g) were equilibrated with 5 mM calcium chloride (CaCl2) solutions (50 mL) at five zinc chloride (ZnCl2) concentrations (0 to 80 mg Zn L–1). The experimental sorption data were fitted with the Freundlich equation. The amounts of Zn sorbed by soil (QZn) at different Zn concentrations in the equilibrium solution (CZn) were closely related to cation exchange capacity (CEC) and pH, that is, to the available exchange sites at given pH values. More specifically, an excellent correlation was found between Zn sorption and exchangeable calcium (Caex), which evidently also depends on CEC and pH. A unique equation was proposed to predict QZn from CZn and Caex in the range of Zn loading covered in our research, that is, from traces to QZn ≈ 60 mg Zn kg–1.