Reuse of the spent mushroom substrate in a vegetable seedbed

The agronomic use of spent mushrooms substrate (SPCHs) in a substrate seedbed could be an interesting alternative for the reuse of these residues in line with the European circular economy strategy. This work evaluates the potential use of four treatments with different SPCHs, Agaricus mushroom (-Ch), Pleurotus mushroom (-St), composting of Agaricus (-CO), and a mixture of SPCH (SPCH-Ch and SPCH-St), as a substrate for lettuce and chilli pepper seedbeds. The experiment was performed in a germination chamber using commercial compost as a control treatment. The evaluation was carried out based on its chemical characteristics (salinity, N and C content), physical properties (bulk and real density, porosity and water retention) and the effect on the plant (germination and biomass). According to the chemical properties studied, the high salinity in SPCH-Ch and SPCH-CO was a limiting factor for the development of the horticultural species evaluated (electrical conductivity1:2.5; w/v; similar to 11 dS m(-1)), low percentages of germination were observed. Regarding the physical properties, porosity and water retention, it was the SPCH-CO, SPCH-St, and mixture treatments that presented some values outside the optimal range established for germination substrates. In the case of SPCH-St, its high C/N ratio could be a limitation in the supply of N to the crop. In relation to the biomass production (aerial and root) of lettuce and chilli pepper, all the evaluated treatments obtained similar values to the control treatment. The treatment of the mixture showed the largest biomass which was significantly higher in lettuce crop. In general, the mixed treatment seems to be the best alternative for use in the seedbed.