Circular use of nutrients in soilless strawberry cultivation: spent growing media as key element

Recycling of nutrients (N, P and K) in spent growing media (SGM) at the end of soilless cultivation is crucial in the framework of circular horticulture and environmental sustainability. SGM may suffer from high nutrient and salt concentrations, reducing their capacity for recycling through direct use as soil amendment or reuse as growing medium, or through use as bulking agent in composting or feedstock for biochar production. The potential of direct reuse of the spent growing medium of strawberries after sanitation or after use as feedstock for biochar or compost production was assessed based on the characteristics of these products. As the upcycled spent growing medium already contained high nutrient levels, the fertilizer application in the reused growing medium can be reduced, especially for P and K. Therefore the potential for minimizing the fertilizer doses during reuse of SGM was evaluated. Nutrient availability was assessed for spent peat based growing media from strawberry during multiple reuse, and for biochar based on spent peat from strawberry cultivation.