The soil water contents at the liquid and plastic limits (the Atterberg limits) are widely used in the classification of soils for engineering purposes. Approximately 500 soil samples (129 Ap horizons and 417 B and C horizons) collected over several years as part of the ongoing soil survey program in Saskatchewan were analyzed for texture and Atterberg limits. On about half of the samples water retention (−33 kPa and −1500 kPa matric potential and air dryness), and organic and inorganic C were also determined. The relationship between the Atterberg limits and soil properties was explored through correlation and regression analysis. Clay and organic matter content explained most of the observed variation in the Atterberg limits of the Ap horizons. Clay was the most important independent variable in the B and C horizons, while inorganic C had only a relatively small impact. Key words: Atterberg limits, texture, organic and inorganic C

The variability of oxalate- and dithionite-extractable iron and aluminum throughout the soil profile and their relationship to total iron and clay contents were investigated for soils representative of the Chernozemic, Solonetzic, Luvisolic and Gleysolic soil orders of Saskatchewan. These distributions and relationships are similar for Chernozemic, Solonetzic and Luvisolic soils. They indicate comigration of iron and clay. Oxalate-extractable iron is low and relatively constant throughout the depth of the soil. Dithionite-extractable iron is somewhat higher and always exhibits a maximum in the B horizons. In all but the Luvisolic soils, the ratios of dithionite-extractable iron to clay are significantly higher in the Ae horizon than in the B horizons. This reflects a higher content of dithionite-extractable iron in the coarse clay fraction than in the fine clay fraction of these soils. Gleysolic soils show different relationships in some respects; oxalate-extractable iron equals that extracted by dithionite in the Ae horizon, reflecting the effect of reducing conditions on iron extractability.

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Atomic absorption analyses of pyrophosphate extractions of B horizons from some Luvisolic, Gleysolic and Solods had higher Fe and Al contents when using 0.1% Superfloc and low speed centrifugation than those obtained when using 0.2% or 0.5% Superfloc or when using high speed centrifugation. Laboratories not equipped with a high speed centrifuge should use a method other than Superfloc to clarify the solution or use the recommended colorimetric method.

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