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Reclamation of sodic soils is imperative in many areas where deterioration of land and water resources is in progress. While the chemical mechanisms involved in the reclamation of sodic soils are well described and understood, the in situ physical processes undergoing during the salt leaching and cation substitution are normally not taken into consideration. Three sodic soils mixed with different amounts of gypsum were packed in columns and leached under saturated conditions for a period of time between 1 and 3 mo. Saturated hydraulic conductivity ([K.sub.sat]) was measured and a thin section was prepared for each of the columns. We used scanning electron microscopy (SEM) and image analysis to measure the size and shape of the aggregates and the pores, and correlated these with chemical and physical parameters. We divided the area by the perimeter (A/P) to quantify the size and A/[P.sup.2] to express geometry for both aggregates and pores. The size of the aggregates had a good correlation with the exchangeable Na percentage (ESP), bulk density, pore size, and [K.sub.sat]. There was no significant relationship between pore size and texture, indicating that transport models using particle-size distribution to infer porosity may not be successful in predicting water transport in soils under reclamation. The linear relationship between aggregate size and pore size indicates that the pore space is determined by the packing of the aggregates not the individual particles, this relationship may have implications not only for water transport but for modeling hydraulic properties in general.

Flax (Linum usitatissmum L.) accumulates Na but little is known about factors influencing Na accumulation in seed of this species. We investigated the influence of added Na (0, 44, and 88 mg NaCl-Na [kg.sup.-1] soil) and K (0, 75, and 150 mg KCl-K [kg.sup.-1] soil) on accumulation of these elements by 'Omega' flax grown on an Aeric Calciaquoll in the greenhouse. The principal findings were: (i) vegetative tissue and seed contained up to 5960 and 754 mg Na [kg.sup.-1], respectively, in the absence of added K; (ii) added Na increased and added K decreased Na concentration in both vegetative tissue and seed; (iii) negative Na x K interactions for Na concentration were due to ion antagonism and were largely unrelated to dilution effects; (iv) seed K concentration was increased by added K and little affected by added Na; (v) Na, in contrast to K, accumulated preferentially in older leaf and stem tissues; and (vi) added Na and K had little influence on seed Ca and Mg concentration. Analysis of seed from five flax nursery trials indicated that both genotype and location influenced seed Na concentration. Commercial flax seed is likely to vary considerably in Na concentration due to edaphic factors, particularly Na and K availability, and genetic factors.

The result of the experiment conducted to find the solubilities of the precipitates during evapoconcentration of synthetic irrigation waters shows that the solubilities of the precipitated solids is proportional to the amount of silicon and magnesium present in the solid. The activities of calcium ion and carbonate ion, the mineralization of the organic matter and the presence of metastable forms of calcium carbonate are overestimated due to the oversaturation of calcite in soil solutions.

An analysis of the effect of magnesium on cation-exchange relationships and structural stability of sodic soils with varying Ca/Mg ratios reveals that an increase in Mg/Ca ratio increases the amount of exchangeable sodium. The influence of Mg on the structural stability of sodic soils is determined by calculating saturated hydraulic conductivity.

Analysis of the selectivity of specimen and soil-derived smectites for Cd, involved the estimation of Cd sorption on SWy-l and on clay-sized separates from two smectitic subsoils. Enhancements in sorption activity accompanied those in PH, for the separates. The separates formed Cd in Na+ and Ca2+ electrolyses. A layer edge surface area, which enhanced the contribution of oxide-like complexation reactions of Cd sorption, is partly responsible for the queer behavior of smectites.

The residual benefit of fertilizer potassium (K) on the performance of cotton grown in vermiculitic soil was studied. Cotton grown in plots with residual K had yields averaging 37% over those of controls. The yield response was greater in manured fields versus those treated with mineral fertilizer. Manure increased soil organic carbon content and decreased the rate of K fixation. The maintenance of yield levels in the face of reduced K requirements suggest that soil sodium may be a partial replacement for K under certain field conditions.

A new method for screening the sodium adsorption ratio (SAR) of soils is presented. It uses combinations of pH and electrical conductivity readings from saturated paste to predict whether the SAR is less than 10, and whether additional analyses are required to determine the SAR. It was validated on a large group of diverse soil samples. The sensitivity of the method was found to be 99.4%, but its specificity is only 81.1%. As a screening procedure, it can reduce the need for additional soil analysis by over 50%.