A review of the use of the basic cation saturation ratio and the “ideal” soil

Summary

This review critically examines the basic cation saturation ratio (BCSR) concept, which prescribes specific 'ideal' proportions of exchangeable calcium, magnesium, and potassium for optimal soil fertility. By re-evaluating foundational experiments by Albrecht and Bear—whose work established the concept in the 1940s—Kopittke and Menzies conclude that the prescribed cation ratios do not consistently influence soil fertility or plant growth within ranges typically found in agricultural soils. The authors argue that continued promotion of BCSR-based soil testing and amendment recommendations, despite limited empirical support, leads to inefficient use of agricultural resources.

Regional applicability

This review has direct relevance to United Kingdom soil testing and management practices, as some commercial soil laboratories have adopted BCSR-based interpretation methods. The findings suggest that UK farmers and growers should be cautious of soil testing recommendations based solely on cation ratios, and that soil amendments targeting these ratios may not provide the promised fertility benefits. The critique applies across temperate agricultural regions with similar soil types and testing practices.

Key measures

Exchangeable calcium, magnesium, and potassium concentrations and their saturation ratios; soil chemical, physical, and biological fertility properties; plant growth responses across multiple studies

Outcomes reported

A critical review of the basic cation saturation ratio (BCSR) concept for soil interpretation, examining whether the prescribed 'ideal' soil cation ratios (65% Ca, 10% Mg, 5% K) actually optimise plant growth and soil fertility. The review evaluated evidence from historical and contemporary studies to assess the scientific validity of BCSR-based soil management recommendations.

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