Evaluation of soil analytical methods for the characterization of alkaline Technosols: I. Moisture content, pH, and electrical conductivity

Purpose

Applying standard soil analytical methods to novel soil materials, such as tailings or soils with unusual properties, should be done with caution and with special consideration of potential interferents and possible pretreatments. The aim of this study was to investigate the effects of common variations in methods on calculated total moisture content, pH, and electrical conductivity (EC) of saline alkaline soil materials.

Materials and methods

Bauxite residue (an alkaline, saline–sodic Technosolic material) as well as two saline alkaline soils from coastal and lacustrine environments were dried under various temperatures and atmospheres, and then analyzed for pH and EC at various soil–solution ratios over time.

Results and discussion

Calculated moisture content of all samples increased with drying temperature. Dehydration of gypsum elevated calculated moisture content. Decreases in soil–solution ratio decreased suspension EC and pH in highly alkaline samples. The pH and EC of soil/water suspensions generally rose with equilibration time for bauxite residue; stable values were attained within 24–120 h. Atmospheric carbonation substantially decreased the pH of samples dried at lower temperatures.

Conclusions

Variations in temperature, time, and atmosphere during drying of highly alkaline and saline soil materials influenced calculated moisture content as well as chemical properties such as pH and EC. A drying temperature of 40 °C and drying to constant weight is recommended to minimize these effects. Soil–solution ratio, equilibration time, and sample preparation conditions influenced observed pH and EC, and should be standardized if attempting to compare results between studies.