Clay mineralogy and K/Ca+Mg quantity/intensity relationships in selected alluvial soils of Pakistan

Résumé En

Influence of clay content, clay mineral suite, layer charge density of the fine clay, and structural Fe(II)+Mg content of the clay on the K/(Ca+Mg) quantity/intensity (Q/I) relations were investigated in mixed-mineralogy soils. The Q/I parameters : (1) equilibrium activity ratio of К (ARe), (2) exchangeable К (ExKq) , (3) potential buffering capacity of К (PBC), and (4) К adsorbed on interlayer and wedge site (*Kiw), a new parameter, were calculated using linear and square root regression models on replicated Q/I data from the top four horizons of each of the three soils. Pairwise correlation analysis indicated that AR�e was positively correlated with structural Fe(II)+Mg content of the coarse clay and inversely correlated with percent smectite in the soil . The positive correlation of AR�e with Fe(II)+Mg indicates that such clays with high Fe(II)+Mg contents can support high activity of К in soil solution either because such clays contain unweathered biotite or because these clays have smectites or vermiculites with a trioctahedral structure. The potential buffering capacity of К (PBC) was positively correlated with concentration of mica and smectite in the soils. The new parameter, AKiw increased with clay sized smectite and mica in soil and charge density of the fine clay and decreased with structural Fe(II)+Mg content, an indicator of trioctahedral nature of the clay minerals. The multiple regression analyses suggested that the Q/I parameters can be successfully predicted in these slightly weathered soils containing appreciable labile mica by using quantitative mineralogy, layer charge density of the clay, and trioctahedral character of clay.