Plant Growth and Chemical Properties of Commercial Biochar- versus Peat-Based Growing Media

Peatlands have been irreversibly destroyed by draining and mining for horticulture, in the course of which tremendous amounts of greenhouse gasses were released into the atmosphere. To avoid this in the future, sustainable alternatives are urgently needed to substitute peat as growing media. An appropriate alternative could be biochar, because it has beneficial effects on nutrient availability and retention, water holding capacity, and organic matter stability. In this study, we compared three different commercially available biochar-containing growing media (Palaterra, Sonnenerde, Terra Magica) with three commercially available peat-based growing media (CompoSana, Dehner die leichte, Dehner mit Vorratsdünger), in a randomized greenhouse pot experiment. Pure sand was used as a control and, to test a potential amount effect, we mixed the used growing media with increasing amounts of pure sand (0, 25, 50, 75, and 100 volume % of individual growing media). The consecutive yields of several agronomically relevant cereals (barley, wheat, and maize) were measured in the mixtures mentioned previously. Additionally, the contents of biochar, amino sugar, and polycyclic aromatic hydrocarbons were measured in each pure growing media before and after the growth experiments. Only Sonnenerde exhibited an increased plant yield of 30–40% compared with peat-based growing media. The growing media exhibited no significant differences of chemical soil properties during the experiment. Only slight tendencies are recognizable towards higher fungal community in biochar- and peat-based growing media. A clear fungi contribution was observed in Palaterra, most probably due to the fact that fungi was a production ingredient. Surprisingly, peat-based growing media also contained about 30 g kg−1 black carbon, a polycondensed aromatic carbon typical for biochar. Overall, our results indicated that biochar-containing growing media, especially Sonnenerde, is a potential alternative for peat-based growing media in horticulture and can enhance degraded soils