Composts from Grapevine and Hazelnut By-Products: A Sustainable Peat Partial Replacement for the Growth of Micropropagated Hazelnut and Raspberry in Containers

Abstract

By-products of the agri-food sector are increasingly employed in the production of new organic preparations, with biofertilizer and biostimulating functions, thus reducing the consumption of non-renewable resources and turning production chains towards circular economy and sustainability. Two composts were produced with solid digestate (85%) as a common component and different sources of recyclable materials (15%): vine pruning wood (compost A), or shells and skin of hazelnuts (compost B). The two composts were used in replacement of variable percentages of peat in nursery substrates, and their effects on various growth parameters assessed on micropropagated plants of two widely demanded species: raspberry (compost A) and hazelnut (compost B). Composts revealed microbiologically safe growth conditions, nutritional content suitable for agronomic purposes and levels of heavy metals in compliance with the European standards. The trials demonstrated the possibility for a partial replacement of peat (up to 20% in hazelnut and 40% in raspberry) in nursery conditions, without compromising, and in some cases improving, the vegetative growth and plants nutritional status. Nonetheless, the highly variable hazelnut growth responses highlighted that compost concentration should be fine-tuned on sensitive species to avoid negative effects. In the case of raspberry, the use of these substrates could also be experimented for soilless production. Because of the potential for metals accumulation, analysis on the extended applications should be made prior to considering field applications.