Israela Ravina

On the electrical double layer theory. II. The Poisson—Boltzmann equation including hydration forces

Abstract A Poisson-Boltzmann equation (PBE) is derived with hydration forces acting on the ions in an interface. The equation is solved numerically for different concentrations of NaF and with different surface potentials. The main differences from the Gouy—Chapman theory are the following: lowering of the surface ion concentrations; breaking of the linear connection between the surface charge and the surface electrical field; bending of the differential capacity curves of the double layer; separating in adsorptions of the ion species of the univalent polyelectrolyte. It is shown that for a mixture of the alkali metal chlorides the adsorption increases in the order Li

Effect of late salinization of chia (Salvia hispanica), stock (Matthiola tricuspidata) and evening primrose (Oenothera biennis) on their oil content and quality

Linoleic acid and α-linolenic acid are the main essential polyunsaturated fatty acids that are required in the human diet. The omega-3 essential fatty acids, found in fish and some plants’ seed oil, are linked to a lowered risk of heart disease. In arid and semiarid regions, where water availability is a major limitation in crop production, alternative water resources, such as saline water and treated sewage effluent, are utilized. Oilseed plants, rich in essential polyunsaturated fatty acids, may be considered a highly economic substitute for common field crops irrigated with fresh water. The purpose of the present study was to determine the influence of irrigation with saline water on the oil yield and quality of Salvia, Matthiola and Oenothera plants. We found that salinity affected the oil content and composition of each plant differently. Salinity decreased the oil yield of Salvia plants, increased it in Oenothera and had no effect on Matthiola. Changes were also found in the oils’ composition, which may have clinical implications.

INTERACTIVE EFFECTS OF SALINITY AND CALCIUM ON HYDRAULIC CONDUCTIVITY, OSMOTIC ADJUSTMENT, AND GROWTH IN PRIMARY ROOTS OF MAIZE SEEDLINGS

ABSTRACT Increasing the calcium ion activity in salinized root media has often been shown to ameliorate the inhibitory effect of salinity on plant growth. In order to better define the biophysical mechanisms involved in these growth responses, we investigated the interactive effects of salinity and calcium on hydraulic conductivities and osmotic potential gradients in roots of maize seedlings. The length of the primary roots was reduced by 54% after 4 days of growth in 0.1-strength Hoagland solution salinized with 100 mM NaCl and by 20% when 10 mM calcium was also added to the salinized root medium. Roots showed 69% osmotic adjustment in response to salinization, with or without extra calcium in the root medium. The mean hydraulic conductivity, L, of the apical 4 cm of maize seedling roots was determined by assaying osmotically-induced backflow. The assay was sensitive enough to detect reductions in L induced by lowering the assay temperature from 27 to 14°C. These reductions in L exceeded those caused by...

On the electrical double layer theory. I. A numerical method for solving a generalized Poisson—Boltzmann equation

Abstract Based on asymptotic behavior of the Poisson-Boltzmann equation, a numerical procedure for its solving is suggested. The method may be used both for single and for overlapped double layers and does not depend on the explicit form of the equation. The method is tested by comparing the numerical results with the analytical solution of the equation that was obtained for a 1-1 electrolyte, using the Gouy-Chapman theory. The accuracy of the method is found to be up to the 4th significant digit in a wide interval of the surface potentials.

Model of ammonia volatilization from calcareous soils

A quantitative model of ammonia volatilization from the calcareous soil uppermost 1-cm layer was developed and tested. The model accounts for the following processes: ammonium-ammonia equilibration in the soil solution, cation exchange between calcium and ammonium which results in ammonium distribution between soil liquid and solid phases, nitrification of dissolved ammonium, distribution of ammonia between liquid and gaseous phases and diffusion of gaseous ammonia in the soil air.The combined effect of various characteristics such as soil pH, cation exchange capacity, water capacity and nitrification rate on ammonia losses from various soil types have been studied. The model was validated against experimental results of ammonia losses from different soils for its use as a predicting tool.The model shows that most of ammonia losses can be explained by the interactive effect of high soil pH and low cation exchange capacity. Computations show increased ammonia volatilization with decreasing soil water capacity. Increasing fertilizer application rate has a small effect on percentage of ammonia losses. Increased nitrification rate and shorter “lag” period of nitrification reduce ammonia losses considerably. Good agreement was obtained between model calculations and experimental results of ammonia volatilization from 13 soils.

Change of b-dimension with swelling of montmorillonite

The effect of swelling on the b-dimension of Na-saturated, Upton, Wyoming montmorillonite was re-examined using powdered silicon as an internal standard. After being corrected with reference to the internal standard, the b-dimension did not increase through the entire range of swelling as reported previously. It increased up to a water content of ~3.0g/g montmorillonite and remained constant thereafter. However, the diffraction peak of the internal standard shifted towards lower angles at higher water contents. This shift was attributed to a relaxation of the wetter samples away from the knife edge of the diffractometer. Presumably, a similar relaxation occurred in the earlier study and was responsible for the apparent increase in b-dimension at water contents above ~3.0g/g.The b-dimension of Upton montmorillonite saturated with different cations was determined using powdered silicon and a colloidal quartz impurity as internal standards. The water content at maximal swelling decreased as the b-dimension increased.

Does salinity inhibit maize leaf growth by reducing tissue concentrations of essential mineral nutrients

Abstract Excessive salinity can reduce growth of crop plants in many regions of the world but the underlying mechanisms are largely unknown. We investigated the possibility that inhibition of maize (Zea mays L.) leaf growth by salinity might be associated with loss of capacity to maintain adequate mineral nutrient concentrations in the leaf tissues. Maize plants were grown for 20d in a controlled environment on expanded vermiculite and irrigated daily with nutrient solution containing additional Ca. The effects of salinization with 100 mM NaCl and 20‐fold differences in the strength of the external nutrient solution on root growth, leaf growth, and ion concentrations in leaf tissues were determined. Salinity caused reductions in root and leaf growth. Increasing external nutrient supply to the roots increased growth of control plants but did not increase growth of salinized plants. Moreover, N and P concentrations in the leaf tissues were increased by salinity and Mg concentrations were unaffected. The sma...

Seed yield, oil content, and fatty acid composition of stock (Matthiola incana) under saline irrigation

The influence of irrigation with saline water on the seed yield, oil content, and quality of stock (Matthiola incana), an oilseed plant rich in omega-3, was studied under greenhouse and field conditions as part of a study to assess the potential of stock to replace low cash field crops in areas of marginal water use due to water scarcity. Water of electrical conductivity ≤6 dS/m did not have a negative effect on yield parameters. Total yield, seed number, and oil content were not affected by salinity, whereas the content of omega-3 was significantly increased.

Effects of salinity stress and calcium on hydraulic conductivity and growth in maize seedling roots

Abstract The underlying mechanisms by which excessive salinity reduces plant growth are not well understood. A few reports indicate that salinity reduces the hydraulic conductivity of the roots in salt sensitive legumes such as bean and lupin: However salinity had little effect on root conductivity in barley, a cereal plant which is relatively salt tolerant. In order to determine whether roots of other cereal plants respond like those of barley, we investigated the effects of salinity on root growth and root hydraulic conductivity in maize seedlings. The length of the primary roots was reduced by 54% after 4d exposure to 0.1 strength Hoaglands solution salinized with 100 mM NaCl. Root length was only reduced by 20% when 10 mM calcium was also added to the salinized root medium. Salinization with 100 mM NaCl reduced hydraulic conductivity in the apical 4 cm of the primary roots by 80% (from 4.7±1.5x108 m/s/MPa to 1.0±0.3xl0‐8 m/s/MPa) and by 51% when 10 mM calcium was also added.

Rheological electrokinetic phenomena in a single capillary

Abstract A numerical simulation of rheological electrokinetic phenomena in a rectangular capillary slit is reported. The theological state of the vicinity water in the capillary is based on the Babchin—Piliavin—Levich model of the viscoelectric effect. The electrical field of the diffuse double layer is considered as the cause for the non-Newtonian behaviour of the interface water layers. A special numeric procedure is suggested to solve the closed system of equations which describe the generalized flows through the capillary. The solution for a particular case (10−5 N KCl water solution, 2 μm x 0.6 cm x 1 cm capillary slit) is presented and discussed. An approximate linear relation between the driving forces and the total current and volume fluxes is obtained and used to determine the phenomenological kinetic coefficients. The electrokinetic ζ-potentials which are functions of the surface charges (potentials) and external conditions are predicted. It is found that ζ-potentials may be different for different electrokinetic experiments. The results are compared with predictions based on a classical viscous flow model.