Fig. 3. The interaction parameter, , as a function of the solid–liquid surface tension, _SL. On each graph, the filled point represents the interaction parameter for water (_w). OR = orange orchard cover soil; PN = pine cover soil; EP = eucalyptus cover soil; LCh and PCh = organic matter extracted from leonardite and sphagnum moss, respectively, with chloroform; and LEt and PEt = organic matter extracted from leonardite and sphagnum moss, respectively, with ethanol.