Hydraulic Performance of Horticultural Substrates—1. Method for Measuring the Hydraulic Quality Indicators

Besides nutrient composition, the hydraulic performance of horticultural substrates is a main issue for evaluating their quality for horticultural purposes. Their water and air capacity and their suitability for transporting water are important hydraulic quality indicators. Shrinkage and water repellency could have a negative impact on storing and transporting water and solutes. The commonly used methods and devices for quantifying the water retention properties of horticultural substrates (sand box, pressure plate extractor) are outdated. The measurements are time-consuming, the devices are expensive, and the results are affected by uncertainties. Here, the suitability of the extended evaporation method (EEM) and an associated HYPROP (HYdraulic PROPerty analyser, device was successfully tested for very loosely-bedded horticultural substrates. EEM and HYPROP enabled the simultaneous and effective measurement of the water retention curve and the unsaturated hydraulic functions. The measurement time of horticultural substrates ranges between 7 and 10 days. Furthermore, the shrinkage properties and the water rewetting time can be measured with the HYPROP system. Results using 18 horticultural substrates are presented. These results are discussed and compared with natural organic and mineral soils showing the specific hydraulic performance of substrates for horticultural applications.