PhD defence - Fritz Julius Asmus Theden-Schow

Hailed as the most important invention of the 20th century, mineral fertilizers have become a defining feature of the highly productive modern agricultural sector, enabling food production for over eight billion global citizens.

Around half of global crop supply has been estimated to rely on fertilizer use, although this reliance carries substantial ecological costs. Their production contributes to greenhouse gas emissions, while their field application is associated with nutrient discharges, soil degradation, and the transgression of key planetary boundaries.

These concerns have intensified calls for a transition toward a circular bioeconomy, one that centers on the circular use of biological materials and the recovery of nutrients from secondary resources.

Processed forms of organic fertilizers are often highlighted as a promising component of this transition, offering lower greenhouse gas emissions in production and reduced nutrient leaching post application compared to conventional mineral fertilizers. Despite this potential, expert stakeholders emphasize that the growth of processed organic fertilizers is constrained by limited access to suitable feedstocks, with few concentrated and readily accessible or inexpensive raw material sources remaining.

Against this backdrop, this dissertation examines the economic feasibility of establishing a novel value chain for marine-based organic fertilizers, an option with both historical precedence and promising agronomic performance. Realizing such a value chain, however, depends on a constellation of factors: biochemical suitability, technological readiness, logistical practicality, and, above all, economic conditions.

Through five interconnected research papers, I investigate both the supply and demand sides of this prospective value chain through an economic lens.

I assess the quantity, utilization, and economic potential of marine by-products; explore producer perspectives on technological, regulatory, and organizational constraints; and evaluate organic arable farmers’ willingness to adopt marine-based fertilizers. The findings indicate that substantial quantities of underutilized marine by-products remain available, even though utilization rates and prices have risen as materials once considered waste increasingly enter higher-value markets.

Ultimately, fertilizers remain a relatively low-value end use and therefore face competition from alternative, more profitable applications of marine by-products. Economic viability therefore depends strongly on how farmers value these products and how much producers are in turn able to pay for raw materials.

Transport and transaction costs, contaminant risks, nutrient content, and prevailing organic fertilizer market conditions are additional factors that emerge as being critical. Persistent stakeholder concerns—particularly regarding PFAS, heavy metals, and supply reliability—underscore that establishing such a value chain is a complex undertaking.

Overall, the dissertation argues that while the market introduction of this novel product group shows significant potential, its realization would require coordinated cross-sectoral efforts, systematic raw material testing, and effective information campaigns.