FLOCCULATION-DISPERSION BEHAVIOUR OF ARIDZONE SOIL CLAYS AS AFFECTED BY ELECTROLYTE CONCENTRATION AND COMPOSITION

摘要

Soil structure is affected by the floceulation-dispersion behaviour of the clay fraction and is of major concern in the irrigation of arid-zone soils. The dispersion characteristics of seven calcareous. arid-zone soils of the Khro river basin (Spain)were determined upon reaction with solutions of variable electrolyte concentration (C), sodium adsorption ratio (SAR) with either Ca or Mg as the divalent counter-ion, and pH, The turbidity (T) of the supernatant soil solution was linearly related (P < 0.01) with the amount of dispersed clay. and. was used as a reliable index of dispersion. The flocculation value (FV) and the stability index (SI) were estimated from the piecewise linear response function established between the turbidity and the electrolyte concentration values of a given SAR. KV increased and SI values decreased as SAR increased. The FVs were much greater than the values reported in the literature for the corresponding reference clavs. Similar FV and SI values were obtained using Ca or Mg as counter-ions. The negative effect of increasing pH values on the enhancement of clay dispersion was only important for electrolyte concentrations below the FV. The FV and SI values and the pH effect varied substantially among these arid-zone soils which were of similar mineralogy (mica and chlorite as predominant clays), indicating that other unknown variables had an important efleet on their dispersive behaviour.