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Paraskevi A. Londra, Maria Psychoyou, and John D. Valiantzas

Urea–formaldehyde resin foam has been introduced as a synthetic organic soil amendment and is used in hydroponic systems, soilless cultures, production of container-grown plants, roof gardens, and sports fields. To evaluate whether urea–formaldehyde resin foam can improve physical properties (water retention capacity and aeration) of horticultural substrates, an organic substrate (coir) and an inorganic soil (loam soil) were selected and amended with urea–formaldehyde resin foam (Fytocell). Water retention curves, θ(h), saturated hydraulic conductivity, Ks, and the relationship between unsaturated hydraulic conductivity and volumetric water content, K(θ), were determined for Fytocell, coir, loam soil, mixtures of coir/Fytocell (60/40 v/v), and loam soil/Fytocell (60/40 v/v). Water retention curves indicated that the addition of Fytocell in loam soil and coir mixtures increased and decreased, respectively, the water retention capacity. The Ks of loam soil and coir mixtures were decreased and increased, respectively, by the addition of Fytocell. In all substrates studied, K(θ) decreased sharply when θ decreased from 0.80 to 0.20 m3·m−3. However, the coir/Fytocell mix had the highest values of K(θ) when θ was below 0.40 m3·m−3. Moreover, the comparison between estimated K(θ) values obtained using the experimental outflow method of and predicted values using the van Genuchten–Mualem model showed a satisfactory agreement (0.937 0.996) for the substrates examined.