EDAFOLOGÍA, Vol 12. (3), pp 173-185 2005
ADSORCIÓN Y DESORCIÓN DE POTASIO EN SUELOS DE GALICIA (ESPAÑA) DESARROLLADOS SOBRE DISTINTOS MATERIALES DE PARTIDA
C. LÓPEZ-MATEO, E. ÁLVAREZ, M.L. FERNÁNDEZ-MARCOS∗
Departamento de Edafoloxía e Química Agrícola, Escola Politécnica Superior, Universidade de Santiago de Compostela, 27002 Lugo. España. *[email protected]
The potassium sorption capacity of soils is a major factor determining the dynamics of this element in the soil-plant system and the requirements for potassium fertilisation. Low contents of available potassium are often a factor limiting crop yield in Galician soils. Potassium sorption depends on the nature of clay minerals; the hydroxy-aluminium vermiculites, common in surface horizons of Galician soils, bes- tow on them a capacity to fix potassium. The present paper studies potassium sorption and desorption by samples representative of A and B horizons of Galician (NW Spain) soils, developed from various parent ma- terials. The mineralogical composition of the soil clay was studied by X-ray diffraction analysis; the presence of non-crystalline materials was tested using the pH in NaF and estimated by the aluminium and iron ex- tracted by acid oxalate. Potassium sorption was determined by shaking the soil samples with 0.01 M CaCl2 containing various K concentrations, until equilibrium is reached. In most cases the experimental data fit- ted best to the linear or Freundlich models, so that it is not possible to predict a limit for potassium sorption by these soils. The sorption energy is higher in soils richer in non-exchangeable potassium. Soils with high contents of non-crystalline materials show a small potassium sorption capacity. The exchange complex con- tributes notably to potassium sorption. Potassium desorption was determined by shaking the soil samples, after the sorption experiment, with 0.01 M CaCl2. Some of the studied soils showed a pronounced hystere- sis.
Key words: potassium sorption, sorption isotherms, potassium desorption, potassium fertilisation, potassium fixation, clay mineralogy, parent material, Galician soils.