Scalable biochar-enriched agriculture model assessing financial viability of the sustainable temporary use for brownfields: the Špitálka case

Introduction Brownfield sites present significant urban development challenges across Europe, often remaining unmanaged due to the substantial costs of physical restructuring and a lack of systematic funding, even for transitional uses. This research addresses the financing gap in temporary urban agricultural projects on brownfield sites. Specifically examining social farming and community garden models as vehicles for financial self-sufficiency, framed within the principles of a circular economy encompassing nutrient recycling, waste valorization, and extended land use cycles. Methods The study employs a simulation model based on life cycle costing and net present value to analyze project survival from the perspective of a municipal investor. The model was applied to the Špitálka brownfield site in Brno, Czechia, as a linearly scalable case study. The analysis integrates diverse revenue streams, including voluntary carbon certificate markets, various national and EU subsidy programs, and raised bed rental revenue. The economic viability of installing raised garden beds containing biochar-enriched soil was evaluated across two project variants: a Social Farming model and a Community Garden model. Results The results indicate that while carbon offsets are economically marginal, the strategic combination of labor and establishment subsidies is the decisive factor for financial survival. The Community Garden variant demonstrated a higher potential for self-sustainability (BCR > 1.0) due to its lower labor intensity and user rental income. Conversely, the Social Farming variant requires a subsidy of nearly 100% to achieve a break-even threshold (NPV = 0). Discussion While the Community Garden model shows stronger prospects for financial independence, the Social Farming variant serves as a vital social cohesion tool whose value extends beyond purely economic metrics. The findings provide a framework for municipalities to temporarily transform abandoned post-industrial areas before their ultimate redevelopment into productive urban spaces that generate societal, environmental, and fiscal benefits. JEL classification R14, R52, Q24