C. LÓPEZ MATEO, E. ÁLVAREZ, M.L. FERNÁNDEZ MARCOS
Universidad de Santiago de Compostela. Departamento Edafología y Química Agrícola. Escuela Politécnica Superior. 27002 Lugo. España.
Abstract. Various forms of potassium were determined in A and B horizons from soils developed from different parent materials (granite, Villalba schist, Órdenes schist, slate, amphibolite and serpentinite) in Galicia (NW Spain). Soluble and exchangeable potassium were higher in surface than in subsurface horizons (0,9 and 0,6 respectively mmol/kg average soluble potassium; 2,9 and 1,9 respectively mmol/kg average exchangeable potassium). Non-exchangeable potassium was generally higher than soluble and exchangeable potassium and ranged widely (from 0 to 64,6 mmol/kg). This variability was not related to depth but to type of parent material, clay mineralogy and soil use. The highest non-exchangeable potassium concentrations were found in soils developed from schists, particularly in those with hydroxy-Al vermiculites or interstratified mica-vermiculite and in fertilised soils.
Keywords: potassium, soluble potassium, exchangeable potassium, non-exchangeable potassium, hydroxy-Al vermiculite, interstratified minerals