CATION-EXCHANGE CAPACITIES OF UPLAND SOILS IN EASTERN CANADA

Relationships between cation exchange capacity (CEC), clay and organic carbon contents and soil pH were analyzed by way of multiple regressi ons for upland soils in eastern Canada (mostly Ontario, with additiona l data for New Brunswick). This was done by vegetation type in an atte mpt to explain some of the otherwise unexplained CEC variations. Data were taken from about 2000 soil horizons (organic L, F, and H horizons as well as A, B, and C mineral soil horizons) under broadleaves (most ly maples, beech, birch or aspen as dominant species), conifers (mostl y fir, spruces and/or pines), and grass vegetation. For the organic fo rest floor horizons (or L, F, and H horizons), both organic carbon con tent (%) and pH were highly significant predicting CEC, i.e., CEC (L, F, and H of broadleaves) = -38 + 0.71 x org. C (%) + 10.3 x pH (R(2) = 0.69), and CEC (L, F and H of conifers) = -31 + 0.34 x org. C (%) + 1 2.1 x pH (R(2) = 0.58). For the mineral soil, clay and organic carbon contents (%) and pH were highly significant for predicting CEC. Soils with forest vegetation were found to have lower contributions of organ ic matter to CEC than grassland soils, i.e., CEC (forest soils) = -7.0 + 0.29 x clay (%) + 0.82 x org. C (%) + 1.4 x pH (R(2) = 0.72), CEC ( wooded grasslands) = -6.0 + 0.31 x clay (%) + 1.31 x org. C (%) + 1.0 pH (R(2) = 0.74), and CEC (grasslands) = -8.3 + 0.24 x clay (%) + 2.14 x org. C (%) + 1.3 x pH (R(2) = 0.79). Relationships that were develo ped from Ontario data for specific vegetational types (maple sites, st rongly podzolized conifer sites, grasslands/croplands) were tested by comparing CEC predictions with reported values for similar sites in Ne w Brunswick and Quebec. The predictions were consistent with the gener al trends for maple sites and grasslands/croplands, but CEC values wer e strongly overpredicted for Podzolic subsoils on conifer sites. Liter ature information of the CEC dependency on in situ pH is sparse. Exist ing information that is based on buffering grassland/cropland soil sam ples from pH 2.5 to 8 appears to mimic this dependency quite well.