Using miscanthus and biochar as sustainable substrates in horticulture: An economic and carbon footprint assessment of their primary and cascading value chains

Abstract

Conventional substrates like peat, stone wool and coconut coir are responsible for high greenhouse gas emissions in the horticultural sector, necessitating low-emission and cost-efficient alternatives. Herein, using miscanthus and biochar as substrate components as well as in cascading substrate application can be alternative practices in a sustainable bioeconomy. However, the carbon footprint and economic impacts of these practices in relation to crop yields have not yet been investigated. Hence, we combined life cycle carbon footprint assessment and costing to analyze the Global Warming Potential and value chain costs of horticultural substrates in tomato cultivation in North-Rhine Westphalia. We conducted a comparison between conventional substrates (peat, stone wool, and coconut coir) and single use and cascading miscanthus-based substrates with and without 1–2 % biochar addition of the miscanthus mass. Also, a subsequent scenario analysis was carried out to examine alterations in inputs and costs.Our results demonstrate that miscanthus-based substrates are climate-friendly and low-cost alternatives to the conventional practices. Switching to miscanthus-based substrates results in more emission savings than other input scenarios investigated. Additionally, incorporating biochar and adopting cascading methods contribute to lower emissions. Notably, biochar has the most significant impact, as its amount correlates with higher emission reductions. Additionally, costs for cascading miscanthus-based substrates are lower compared to conventional substrates. Overall, there is only a slight variance in costs between conventional and miscanthus-based substrates. However, with the introduction of carbon emission pricing and carbon removal certificates, miscanthus-based and biochar-containing substrates may emerge as more cost-efficient alternatives. Thus, by advancing financial instruments on carbon emissions and removal, introducing cascade use within and beyond the horticulture sector, and supporting cultivation of sustainable biomasses, miscanthus and biochar can effectively contribute to the development of a sustainable bioeconomy.