Benefits and drawbacks of combined plant and mushroom production in substrate based on biogas digestate and peat

Production of plants and mushrooms in substrate based partly on anaerobic digestate from biogas production (30%) and peat (70%) was studied in experiments performed using oyster mushroom (Pleurotus ostreatus) and basil (Ocimum basilicum). Biogas digestate was included in order to decrease use of peat and fertilizer. In separate experiments, combined greenhouse production of mushrooms and plants in fresh substrate, mushroom production in bags of fresh substrate or spent substrate from plant production, and plant production in spent substrate from mushroom production were studied. In terms of plant yield, positive impacts of combined culture were observed, with significantly higher yield of basil when mushroom spawn was added to fresh substrate at a concentration of 2% (p = 0.04). Increasing the concentration to 10%, which was sufficient for fruiting body formation in parallel with plant production, did not increase basil yield compared with the control. When fresh substrate was partly replaced with spent substrate from mushroom production, significantly higher yield of basil was obtained (p = 0.001). Mushroom production had an impact on the nutritional composition of the substrate, resulting in changes in nitrogen dynamics, a significant decrease in phosphorus concentration by 14% (p = 0.001), and a change in extractable concentrations of five of 10 elements studied. In terms of mushroom yield, the impacts of combined production with plants were generally negative. [Display omitted] •Plant yield increased on including mushroom spawn (2%) in the substrate.•Plant yield increased on including spent mushroom substrate in the substrate.•Combined production is possible, but low-yielding considering both mushroom and plant.•For mushroom production, inclusion of plants in the growing system was less useful.