Biochar effects on potassium availability and dynamics in Egyptian soils

Potassium (K) deficiency remains a major constraint for sustainable crop production in Egyptian soils, especially in calcareous and sandy soils. This study evaluated the effectiveness of four types of biochar in enhancing K availability and dynamic across four varied soil textures. Four biochars (bagasse biochar (BB), olive stone biochar (OSB), orange fruit waste biochar (OFB), and maize stalk biochar (MSB)), were applied at uniform rate of 3% (w/w) to sandy, loamy, clayey, and calcareous soils. Key indicators including such as; water-holding capacity (WHC), cation exchange capacity (CEC), labile-K (KL), activity ratio of K ( $$\:\text{A}{\text{R}}_{0}^{\text{K}}$$ ), potassium buffering capacity (PBCK), and Gibbs free energy (ΔG) were measured to assess K dynamics and thermodynamic parameters. The studied soil properties, including WHC and CEC, were increased by 35.50%, 65.85% in sandy soil with MSB, 30.34%, 30.70% in loamy soil with MSB biochar, 17.10%, 18.20% in clayey soil with MSB biochar, 20.20%, 33.5% in calcareous soil with MSB biochar. Thermodynamic K parameters also improved in all studied soils, especially when treating with MSB and OSB biochars. In sandy soil, the application of maize stalk biochar increased KL by 376% and $$\:\text{A}{\text{R}}_{0}^{\text{K}}$$ by 358%. The olive stone biochar applied in loamy soil increased KL by 72.7% and $$\:\text{A}{\text{R}}_{0}^{\text{K}}$$ by 69.8%. The application of maize stalk biochar in calcareous soil increased KL and $$\:\text{A}{\text{R}}_{0}^{\text{K}}$$ values by 103% and 88.8%, respectively. Orange fruit waste biochar had the highest K content as a waste material. The Gibbs Free Energy values became more negative after the application of the biochars. The values of KL, $$\:\text{A}{\text{R}}_{0}^{\text{K}}$$ , and the Gibbs Free Energy were interrelated. Results also confirmed the distinctiveness of OSB and MSB, as their surface area reached 28.87, and 32.14 m² g− 1, respectively, and their content of multiple functional groups. Biochar amendments, particularly MSB and OSB biochars, substantially improve K availability, retention, and energy efficiency in Egyptian soils. These results highlight biochar as a strategic input for restoring K in soil, enhancing nutrient cycling, and promoting sustainable soil management under arid and semi-arid conditions.