Assessing sewage sludge-made biochar and compochar (compost+biochar mix) as horticultural soilless growing media

While biochars are extensively used as soil amendments in regenerative agriculture, their use as a soilless growing media is less common. Particularly in horticulture, this use may enable crop production in harsh conditions, such as extreme air temperatures or high soil salinity. A soilless biochar-based growing media can replace conventional growing media, thereby minimizing their extraction and consequent severe damages to natural environments. Combining biochars with other biological or mineral non-charred materials may further improve medium quality. In this study, we assessed the use of biochar and compochar (a mix of biochar + compost) – both produced from human sewage sludge – as an alternative growing media for commercial tuff (tephra). We studied the productivity of lettuce and cherry tomato grown on three growing media, and investigated the chemical and biochemical properties of the media. Overall, both crop productivity and media quality were greater under biochar and compochar than these under the tuff. As such, the importance of this study stems from demonstrating the potential of using domestic sewage sludges to produce growing media that supports agronomic productivity, while decreasing the overall anthropogenic footprint on the environment.