Different Miscanthus genotypes as growing media in soilless tomato cultivation and its subsequent use for combustion

Miscanthus was used as an alternative growing media to replace stone wool or coconut coir in soilless tomato cultivation in Europe. We tested three different Miscanthus genotypes (M. x giganteus in two different processing types, M. sacchariflorus 'Robustus', and M. sinensis). Besides plant performance, substrates were characterized by their pH and electrical conductivity (EC) values over cultivation time. To evaluate possible cascading use of Miscanthus media after end of cultivation, combustion quality (calorific value, ash content) was measured. Results showed that the cumulative marketable tomato yield until truss 12 was highest on coco coir, followed by the different Miscanthus substrates. Stone wool had the lowest yield. Blossom-end rot (BER) incidence on stone wool was about two times higher than on Miscanthus substrates, and on coco coir it was lowest. While EC values in Miscanthus substrates and coconut coir remained almost constant over cultivation period with values around 2.0 to 3.0 dS m(-1) (with a maximum of 4.9 dS m(-1) for coco coir), EC on stone wool showed a higher variation ranging from 1.6 to 6.5 dS m(-1). pH values for Miscanthus substrates ranged between 6.1 and 7.8, for coco coir between 5.5 and 6.5, and for stone wool between 3.8 and 7.4. After using Miscanthus as growing media, combustion quality of the different substrates was compared to the original feedstock. While calorific values were comparable, the ash content increased after use. The study showed that Miscanthus is a promising sustainable growing media for tomato production in soilless cultivation. Further studies may lead to optimization of the substrate. Moreover, it can be used for subsequent uses like direct combustion.