Development of alternative growing media with HTC coal and evaluation of their hydro-physical quality
Bog peat is a finite resource but still forms the main component for the production of growing media. The search for alternatives for the substitution of bog peat is a sustainable objective. Hydrothermally carbonized plant residues (HTC coal) also referred to as hydrochar was made based on three different temperatures (150, 170, and 190°C) and their hydro-physical properties were measured and evaluated. The investigation considered two commercial growing media consisting of bog peat, compost and clay (K1, K2) and three different mixtures of HTC (10, 20, 30%) with K1. In addition, a pure compost K3 was included in the investigations. The hydro-physical properties, water retention curve and unsaturated hydraulic conductivity, were simultaneously measured with the Extended Evaporation Method (EEM) and the HYPROP device (HYdraulic PROPerty analyzer) in triplicate replication per substrate. The basic quality indicators, plant available water, air capacity and capillarity, were derived from these functions. In addition, the shrinkage behavior and the re-wetting properties were measured and included in the evaluation as limiting indicators. The assessment of the hydro-physical suitability was based on a 5-point evaluation framework taking into account the application in flower pots/containers and the field application under free drainage. The evaluation framework consists of two parts, the basic rating - plant available water, air capacity and capillarity and the rating for the hazard factors - shrinkage and re-wettability. The rating of the HTC substrates varied between medium for container and good for field application. The rating of the pure compost K3 was worse. The most critical characteristic of the substrates examined in this experiment was the air capacity in containers which was lower than the threshold value of 10% by vol. Among the limiting indicators only shrinkage at 800 hPa, in few cases, had negative impact on the rating.
Schindler, U., Eulenstein, F., Seiffert, M., Lühmann, T., Frerichs, M. and Gramann, J. (2021). Development of alternative growing media with HTC coal and evaluation of their hydro-physical quality. Acta Hortic. 1305, 219-226
hydrochar, plant available water, air capacity, water retention curve, hydraulic conductivity, water drop penetration time, shrinkage, HYPROP