Estimation of Water Retention Characteristics Depending on the Particle Sizes of Perlite Using van Genuchten Equation with Retention Curve Program

The estimation of water retention for perlite particles, which are used as growth media need to set up for properwater management strategy due to uncertain available water proportion during growth period of vegetablecrops in a greenhouse. The water retention curves (WRC) expressed as volumetric water content (θv) wereconstructed with five different sizes of the expanded perlite after fully saturating and packing the perlite inopen-ended metal cubes at 11 levels of matric potentials from 0 to -1,500 kPa. The best fitted four parametervalues (θs,θr, n, α) of the van Genuchten model (vG model) for the substrate samples were obtained using theRetention Curve Program (RETC) based on the values measured water content at the corresponding matricpotentials. The particle size corresponding to 36.8 percentage by mass of particles was 0.80065 mm. Thecalculated uniformity coefficient and the coefficient of gradation for the perlite were 1.962 and 2.51 mm,respectively. Measured water contents at each matric potential increased with decreasing particle size ofperlite while the difference of water content between saturation (θs) and residual state (θr) increased withincreasing particle size. The mean R2 for all sizes of the perlite particle was suitable to predict θv because themeasured data points did not vary around the estimated regression line. Therefore, PTF performance based onvan Genuchten (vG) equation using data set including perlite particle size can be applicable to estimate waterretention in perlite particles. The estimation of water retention for perlite particles, which are used as growth media need to set up for proper water management strategy due to uncertain available water proportion during growth period of vegetable crops in a greenhouse. The water retention curves (WRC) expressed as volumetric water content (θv) were constructed with five different sizes of the expanded perlite after fully saturating and packing the perlite in open-ended metal cubes at 11 levels of matric potentials from 0 to -1,500 kPa. The best fitted four parameter values (θs,θr, n, α) of the van Genuchten model (vG model) for the substrate samples were obtained using the Retention Curve Program (RETC) based on the values measured water content at the corresponding matric potentials. The particle size corresponding to 36.8 percentage by mass of particles was 0.80065 mm. The calculated uniformity coefficient and the coefficient of gradation for the perlite were 1.962 and 2.51 mm, r