Long molecular chain of polymers with active groups, combined with its complexity and flexibility to different environmental conditions provides an interaction of these groups with the mineral soil clays, thereby qualifying the polymers as soil flocculants effective. This study is aimed at evaluating the pore size distribution and hydro-physical properties of soils with cohesive horizons of the coastal plains of Pernambuco State, Brazil, with the application of anionic polyacrylamide (PAM). Thus, three horizons, one cohesive (Bt1) and two non cohesive (E and Bw/Bt) Ultisol were evaluated and, to compare the cohesive horizons, a BA horizon of Oxisol was selected. PAM aqueous solutions (12.5, 50.0 and 100.0 mg kg-1) and distilled water (control = 0 mg kg-1) were applied in undeformed samples by capillary. Pore volume was evaluated by diameter (macro, meso and micropores), total porosity, saturated hydraulic conductivity (Ksat), soil penetration resistance (PR) and soil-water characteristic retention curve. Polymer solutions reduced Ksat, macroporosity and total porosity of cohesive horizons (micropores dominated). More concentrated solutions increased PR of the Bt1 horizon. The excess negative charges in the system are the main factor for the negative effects of PAM on clay horizons. We hope that less electronegative PAMs may improve the hydro-physical characteristics of cohesive horizons.
Key words: Polyacrylamide, coastal tablelands, soil penetration resistance, negative charges, water retention, macroporosity.