The solubility of Se in seven soils indicate that Se concentration in solution is governed primarily by a ferric oxide‐selenite‐adsorption complex (Se oxidation state +4). However, under certain conditions Se may also exist in the oxidation states +6, 0, and −2. The proportions of Se in the four oxidation states are treated theoretically as they are affected by the redox potential, soil pH, and ions with which Se combines.

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Procedures were developed for the partition of heavy metals (Cu, Co, and Zn) between complexed and uncomplexed forms in soil solution. Competition for the above cations by complexing agents naturally present in soil solution and added complexing agents that form metal complexes soluble in organic solvents was determined by measuring the distribution of metal between aqueous and organic phases in a two-phase system. The degree to which the metal was complexed in the original soil solution could be deduced by comparing the amount of metal extracted from soil solution with that extracted from water at the same pH. Examination of soil solutions from several mineral soils indicated that in the case of Cu as much as 99% of the metal may exist in a complexed form.

At least three groups of compounds were found to complex Zn2+ and Cu2+ in soil solution from the A horizon of a Williamson silt loam. A nondialyzable fraction of soil solution ligands had a poorly defined acid dissociation, pKa, ranging from 3 to 4.7. The dialyzable fraction had acid dissociation constants of 4.5 and 9.5, which were attributed to aliphatic and amino acids, respectively. The equivalent concentration of the nondialyzable acid fraction was only 1/40 that of the dialyzable fraction, but was more effective in complexing Zn and Cu in the soil solution. The average metal/ligand ratio was equal to unity in complexes of both the dialyzable and nondialyzable fractions with Zn2+ and Cu2+. Estimated, log10 (average formation constants) of the nondialyzable‐metal complexes were calculated on the basis of titratable acidity as 4.3 ± 0.1 and 5.5 ± 0.1 for Zn2+ and Cu2+, respectively.

Soil solutions from several areas of the US were analyzed by atomic absorption for total Mn and by resin exchange for percent Mn complexed. Values for the latter (84%–99%) in soil solution from the A horizon were intermediate to those previously reported for Zn and Cu. Soil solution from a New York forest soil at pH 7 contained 13 ppm Mn, of which 93% was complexed. Spectrophotometric and polarographic methods were developed to determine the oxidation state of Mn in this soil solution. Both methods indicated the Mn in solution was present in the +2 oxidation state. The presence of such large concentrations of Mn2+ in a soil solution of a neutral soil was still less than that predicted from measured values of the Eh of the soil solution and the Mn2+/MnO2 half‐cell potential. Soil microorganisms oxidized and precipitated Mn2+, presumably as MnO2, but the presence of the neutral soil solution that contained 13 ppm Mn partially inhibited this precipitation.

The subsoil of a xanthic ferralsol was used to determine the effect of varying ionic strength and pH on the cation exchange capacity and the amounts of Na, K, Ca, and Mg in exchangeable form.The cation exchange capacity increased with both pH and ionic strength from 2.6 meq/100 g at pH 2.5 and 0.01M ionic strength to 6.9 meq/100 g at pH 9.5 and 1.0M ionic strength.Sodium and K remained completely exchangeable over all the ionic strengths (0.01 to 1.0M) and pH range 2.5 to 9.5. By contrast Mg became fixed in nonexchangeable forms as the pH increased so that 62% of Mg originally exchangeable at pH 4.0 was fixed at pH 9.5 and 1.0M ionic strength. Calcium also appeared to become fixed in nonexchangeable form as the pH increased, but to a much lesser extent than Mg.

The Murray Darling Basin accounts for half of all water used for irrigation in Australia. However, improvements in water use efficiency (WUE) are required, owing to increasing demands on water (e.g., environmental flows). This requires data on the spatial distribution of soil-hydrological properties, such as deep drainage (DD). Measuring DD using lysimeters, although accurate, is site-specific. Alternatively, estimates are commonly made using chloride mass balance (CMB) models. Gaining this information across a large area is still problematic due to the prohibitive cost of drilling, sampling, and laboratory analysis. Ancillary data, obtained from electromagnetic (EM) instruments, have been used to add value to a limited number of DD estimates. We evaluated the use of a hierarchical spatial regression technique to map the estimated DD using a steady state CMB model coupled to EM34 measurements. We first compared a standard least squares and a stepwise multiple linear regression model. The former includes the use of EM34 signal data in the horizontal (EM34-10H, EM34-20H, and EM34-40H) and vertical (EM34-10V, EM34-20V, and EM34-40V) dipoles, as well as two trend surface variables (scaled easting and northing). The latter model only includes a statistically significant ancillary variable (EM34-10H) and a trend surface parameter (scaled northing), and we use this to estimate DD across the lower Namoi Valley. EM34 data available on a 1 km grid proved useful for mapping DD on a reconnaissance level, with the results closely related to the physiography. In particular, large DD estimates are associated with the prior stream channels. Conversely, smaller DD estimates characterize the agriculturally significant clay plain which is used extensively for irrigated cotton production. The map of estimated DD will allow improved siting of dams and irrigation fields, as well as indicate where more efficient cropping or irrigation systems can be implemented to increase WUE.

The movement of synthetic chloride solutions, simulating a treated sanitary landfill leachate, through columns filled with the subsoil of a xanthic ferralsol were studied in the laboratory. The chloride movement did not follow the miscible displacement equation or more sophisticated models, because the amount of positive charge carried by the soil depended on both pH and the ionic strength of the solution moving through it. During movement of the alkaline synthetic leachate into the column, the amount of positive charge increased due to the higher ionic strength of the leachate relative to the soil solution. A further temporary increase in positive charge also took place due to the decrease in pH induced by cation exchange caused by the leachate front. Later, the desorption of Cl took place as the alkaline leachate titrated the soil to pH > 9.0 and the positive charge was neutralized by OH adsorption. These results show that variation in the positive charge of the soil, induced by the solution moving through it, causes the Cl outflow curve to deviate from theory. Before more advanced theories of miscible displacement can be applied to this type of situation, it will be necessary to develop adequate kinetic theories to describe the changes in the soil's charge properties induced by the solution moving through it.