Recycling of P and K in circular horticulture through compost application in sustainable growing media for fertigated strawberry cultivation

摘要

Peat replacement by compost in growing media can increase the sustainability of soilless cultivation. Compost, when mixed into growing media, is a source of fiber, i.e., a rooting medium, as well as an important source of nitrogen (N), phosphorus (P) and potassium (K). Physical properties as well as nutrient levels in growing media are known to affect plant growth and health. Therefore we monitored the evolution of nutrient release in compost-amended growing media for strawberry in greenhouse culture with drip fertigation for a double cropping system of cv. Elsanta, i.e., autumn culture with continued culture in spring. Compost amended and other alternative growing media for strawberry production were tested during four years of trials at full-scale level in a professional greenhouse growing system, in order to optimize the new cropping system with alternative substrates. Compost amended substrates contained 20-100% (v/v) compost, with different compost types tested. We assessed effects on yield and nutrients, i.e. nutrient availability in the substrate, uptake in the plants, and losses with the drainage water, as well as effect on diseases and pests (infection by powdery mildew (Podosphaera aphanis), aphids (Chaetosiphon fragefolii), and the anthracnose pathogen (Colletotrichum acutatum)). Adding compost to growing media has potential to increase the sustainability of soilless strawberry culture. Results show that growing strawberries on alternative substrates is feasible, but the substrate mixtures containing compost required adjusted fertigation due to nutrients supplied by the compost. This study revealed that strawberry plants made highly efficient use of the P and K in the compost when P and K input by fertigation was reduced, and that compost addition results in reduced export and potential losses of nutrients with the drain water and spent growing media. In general, the compost-amended substrates with lower N fertigation performed well as a growing medium during the autumn culture, but in the continued spring culture, these substrates needed an adapted fertigation regime for N, P and K. The N supply by the tested composts during the autumn culture allowed for significant reductions in N supplied by fertigation, i.e., 50% reduction when 100% (v/v) compost was used, and 10% reduction when 20% (v/v) compost was used. Degree of infection with powdery mildew and aphids was strongly positively correlated with the N status of the crop, pointing at the risks of high N supply for the crop. At the end of the autumn culture, no significant positive or negative effect of the compost treatments on the latent survival of C. acutatum on the strawberry leaves was found.