<p>Potassium (K), a critical nutrient for crops, is predominantly sourced from finite mineral deposits, raising concerns about sustainability and geopolitical supply risks. This review explores the potential of biological sources including agricultural residues, animal manures, wood ash, and biochar as alternative potassium inputs for sustainable fertilizer production. Biomass-derived ash and phytoliths are highlighted as particularly promising due to their high content of water-soluble potassium salts (e.g., K₂CO₃, K₂SO₄) and compatibility with existing circular bioeconomy frameworks. The review synthesizes current recovery techniques such as water leaching, acid precipitation, pyrolysis, gasification, hydrothermal carbonization, and composting. Advantages, limitations, and trade-offs of each method are evaluated in terms of recovery efficiency, cost, and environmental impact. Emphasis is placed on recent innovations that integrate nutrient recovery with biomass energy systems, contributing to both carbon mitigation and soil fertility. Special attention is given to Southeast Asia – one of the world’s most potash-import-dependent regions, where abundant rice straw, sugarcane residues and silicon-rich phytolith pools present unique opportunities for localized, bio-based K recovery. Finally, key research gaps and policy implications are discussed, particularly in the context of low- and middle-income countries dependent on potash imports. This work advocates for a paradigm shift towards bio-based potassium recovery as a resilient, locally available, and climate-smart nutrient strategy.</p> Graphical Abstract <p></p>