Effective CEC of 230 mineral soil samples was estimated as sum of (Ca + Mg) and (AI + H) displaced by N KCI. The mean values as me/100 g of soil were, in the surface samples, 15.9 ± 2.0 in 46 clay soils, 8.9 ± 1.3 in 21 silt and loam soils, and 8.3 ± 1.1 in 39 sandy soils. In samples from the deeper layers the corresponding means were 16.3 ± 2.3 in 54 clay soils, 5.6 ± 0.9 in 21 silt and loam soils, and 2.5 ± 0.5 in 49 sandy soils. In surface samples of clay soils the mean effective CEC was

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... t two thirds, in sandy soils of deeper layers about one third, and in all other groups about one half of the corresponding average potential CEC determined by neutral ammonium acetate. In the total material in which clay content ranged from 0 to 95%, organic C from 0.1 to 8.7 %, soil pH from 3.3 to 7.5, and oxalate soluble Al from 1.4 to 47.9 mmol/100 g, the »effective CEC» depended mostly on clay content: the partial correlation coefficient r = 0.90***, and the standard partial regression coefficient β = 0.84. The corresponding coefficients for the relationship between the »effective CEC» and the content of organic C were r = 0.55*** and β = 0.29, soil pH r = 0.35*** and β = 0.16, and oxalate soluble Al r = –0.13 and β = –0.06. The positive effect of liming on effective CEC, particularly, in coarser textured acid soils high in organic matter was emphasized.