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Abstract--Adsorption isotherms for water vapor, c-spacing and heat of immersion in water of Naand Ca-montmorillonite were measured at 25~ at various r.h. The amount of water adsorbed as a function of the r.h. increased gradually, whereas the c-spacing increased, and the heat of immersion (per mole of adsorbed water) decreased in steps. There was good agreement between the calorimetric data, the heat calculated from the isotherms by use of BET equation, and the calculations from the ion-dipole model. A model is presented to describe the hydration of sodium and calcium montmorillonite.

Plants are likely to be affected by simultaneous salinity and boron (B) toxicity stresses due to exposure to soils with high levels of naturally occurring salinity and B, or due to irrigation with water containing high levels of salts, including B. Inadequate information regarding the response of plants to the combination of excess B and salinity on plant growth and yield is available, and there is no consensus concerning mutual relations between salinity stress and B toxicity. Growth and yield of bell pepper (Capsicum annuum L.) were measured at different B and salinity levels in two greenhouse experiments. The results from these experiments and from published data for wheat, tomato and chickpea were analyzed according to the Abbott method to define the combined effect of B and salinity on plant growth and yield. Application of the Abbott method for the experiments on peppers generally implied an antagonistic relationship for excess B and salinity. In other words, toxic effects on growth and yield were less severe for combined B toxicity and salinity than what would be expected if effects of the individual factors were additive. Similar antagonistic characteristics were found using data from three of the five studies reported in the literature. The mechanism of relationships between B and salinity in plants is not clear and several options are discussed. Prominent among the possible explanations are reduced uptake of B in the presence of Cl and reduced uptake of Cl in the presence of B.

Abstract--Boron adsorption by Ca forms of montmorillonite, illite, and kaolinite was determined as a function ofpH and boron concentration in solution. Data from batch experiments were compared with results computed for each clay according to fitted adsorption coefficients (maximum boron adsorption and affinity constants related to the binding energy). The agreement between calculated values and experimental results indicates that a phenomenological equation can be used to predict boron adsorption on clays as a function of both of these variables. For the solution-to-clay ratios examined, the water content does not affect the boron-surface interaction as expressed by the above adsorption parameters. Because the affinity of clays for B(OHL-is much stronger than for B(OH) 3 , the adsorption maximum was obtained only under alkaline conditions at approximately pH 9.0 to 9.7. It is suggested that the pH of maximum adsorption is a function of the ratios of affinity coefficients of the three species B(OH)3, B(OH)4-, and OH-competing for the same adsorption sites. The adsorption coefficients indicate that in some cases the difference in the amount of adsorbed boron between montmorillonite and kaolinite could be either small or large, depending on the circumstances. The main factor that would affect this difference is the total amount of boron in the suspension. Estimated value of the adsorption maximum was 2.94, 11.8 and 15.1/zmole/g for Ca-kaolinite, Ca-montmorillonite, and Ca-illite, respectively.

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