Volumetric Water Content ($VWC\%$) alone does not quantify the energy work a plant root must exert to extract water. Matric potential ($\Psi_m$, expressed as suction tension in hPa or $pF = \log_{10}|\text{hPa}|$) dictates water availability across the pore-size distribution. In rockwool slabs, Easily Available Water (EAW) resides tightly between $pF\ 1.0\text{ (10 hPa)}$ and $pF\ 2.0\text{ (100 hPa)}$.
1. The van Genuchten Soil Water Retention Curve
\Theta(h) = \left[ 1 + (\alpha |h|)^n \right]^{-m}, \quad m = 1 - 1/n
Operating beyond $pF > 2.2$ triggers sharp root hydraulic cavitation and stomatal closure.
2. Interactive Matric Potential Engine
Calculate suction tension and pF curves across substrates online: