Reusable growing substrates for circular horticulture
The extraction of peat, for example for ornamental plant cultivation, is under discussion because peatlands are considered a unique habitat for protected plant and animal species. Moreover, the extraction of peat involves significant CO2 emissions. Every cubic metre of peat that we can reuse represents a reduction in CO2 emissions, and thus reduces the impact on the climate and the environment.
That is why the ornamental plant cultivation company JoLuPlant NV in Staden has been investing for two years in upgrading and reusing cultivation substrates based on peat from strawberry and cucumber growers in the area. We believe that we can process cultivation substrates into reusable, high-quality potting soil, which we can reuse as a raw material for another crop, for example chrysanthemums.
Through this project, together with the Proefcentrum voor Sierteelt (PCS) and the Instituut voor Landbouw- en Visserijonderzoek (ILVO), we want to take a close look at the storage and processing in our recycling process and, where necessary, adjust, optimise and make it more sustainable. For instance, we want to investigate and test the efficiency of our steam treatment for fungi, insects and weed seeds. We will assess the quality of the recycled substrate and examine whether fertilisation needs to be adjusted. We also tested the steamed substrate for some typical ornamental plants in the cutting and propagation phases. Finally, we have also tested our process against the legal framework.
Pieters Jozef en Luc
PartnersProefcentrum voor Sierteelt vzw (PCS), Instituut voor Landbouw- en Visserijonderzoek (ILVO)
Our heating process (steaming at 100°C and storage for 1 hour at 70°C) is efficient in killing the tested plant pests and weed seeds. We did not find any problems with diseases or pests during the tests with cuttings or plants.
The steamed substrate has a relatively high pH and still contains many nutrients. We can adjust the fertilisation of the next crop to this.
We tested the steamed substrate with cuttings and compared it to reference substrates. The cuttings in the steamed substrate had an equal root development, higher plant height and biomass, higher phosphorus and potassium uptake but lower chlorophyll content.
The recycled substrate was tested for further cultivation of chrysanthemums. There, we noticed that the substrate did not provide enough nitrogen, but it did provide enough phosphorus, potassium, calcium and magnesium. An extra source of nitrogen will be needed for good growth.
MOST IMPORTANT LESSONS LEARNED
From our tests, we may conclude that the steamed substrate can be reused as a cutting and cultivation substrate, but that we must check per cultivation whether extra nitrogen is needed. The other nutrients can be supplied by the steamed substrate.
It is important that above-ground plant residues are removed from the substrate, or that the substrate is stored for a sufficiently long time before steaming and then remains at the temperature for a sufficiently long time before cooling.
Our recycling process fits within the legal framework (cfr. Art 36 of the Materials Decree): we avoid peat extraction and perlite production, we avoid the injudicious use of the nutrients in the used cultivation substrates and we directly reuse the already present nutrients in the used cultivation substrates.
1hourly storage at 70 °C gives an equivalent substrate
WHAT DOES THE FUTURE HOLD?
This recycling model can give the ornamental plant grower more control over the availability and composition of cuttings and growing substrates. The economic feasibility of steaming within the own company strongly depends on the company, but for JoLuPlant, this activity already yields cost savings.
The results of the project were presented at various events. We exchanged our experiences with other growers who are also experimenting with steaming and reusing the removed substrates. It is clear that the potential of this idea is great: the sector is asking for it and the results are very positive.