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For effective irrigation and fertilization management, the knowledge of substrate hydraulic properties is essential. In this study, a steady-state laboratory method was used to determine simultaneously the water retention curve,  θ ( h ), and unsaturated hydraulic conductivity as a function of volumetric water content,  K ( θ ), and water pressure head,  K ( h ), of five substrates used widely in horticulture. The substrates examined were pure peat, 75/25 peat/perlite, 50/50 peat/perlite, 50/50 coir/perlite, and pure perlite. The experimental retention curve results showed that in the case of peat and its mixtures with perlite, there is a hysteresis between drying and wetting branches of the retention curve. Whereas in the case of coir/perlite and perlite, the phenomenon of hysteresis was less pronounced. The increase of perlite proportion in the peat/perlite mixtures led to a decrease of total porosity and water-holding capacity and an increase of air space. Study of the  K ( θ ) and  K ( h ) experimental data showed that the hysteresis phenomenon of  K ( θ ) was negligible compared with the  K ( h ) data for all substrates examined. Within a narrow range of water pressure head (0 to –70 cm H 2 O) that occurs between two successive irrigations, a sharp decrease of the unsaturated hydraulic conductivity was observed. The comparison of the  K ( θ ) experimental data between the peat-based substrate mixtures and the coir-based substrate mixture showed that for water contents lower than 0.40 m 3 ·m −3 , the hydraulic conductivity of the 50/50 coir/perlite mixture was greater. The comparison between experimental water retention curves and predictions using Brooks-Corey and van Genuchten models showed a high correlation (0.992 ≤  R  2  ≤ 1) for both models for all substrates examined. On the other hand, in the case of unsaturated hydraulic conductivity, the comparison showed a relatively good correlation (0.951 ≤  R  2  ≤ 0.981) for the van Genuchten-Mualem model for all substrates used except perlite and a significant deviation (0.436 ≤  R  2  ≤ 0.872) for the Brooks-Corey model for all substrates used.

Simultaneous Determination of Water Retention Curve and Unsaturated Hydraulic Conductivity of Substrates Using a Steady-state Laboratory Method