Increasing the Fertilizer Efficiency of Potassium Silicate by Co-Pyrolysis and Chemical Activation

Brazil relies on imported potassium (K) fertilizers despite having reserves of K silicate rocks, such as glauconite. There is an interest in pyrolysis to produce biochar as a nutrient source for crop growth. So far, few studies have explored the pyrolysis on increasing K availability from silicate rocks. We aimed to evaluate the effect of co-pyrolysis of coffee husk with different proportions of glauconite with and without KOH activation on K solubility and in maize growth. Maize was cultivated under greenhouse conditions and received K fertilization (300 mg kg^− 1) through coffee husk biochar, coffee husk biochar co-pyrolyzed with 10%, 25%, and 50% of glauconite, coffee husk biochar co-pyrolyzed with 10%, 25%, and 50% of glauconite and 5% KOH, pristine glauconite, pyrolyzed glauconite, pyrolyzed glauconite with 5% KOH, a commercial dose of glauconite (10% of K₂O), KCl (positive control), and control without K. Maize was grown for 57 days, and after harvest, the soil was analyzed to determine K availability. The results showed that KOH activation increased K solubility, resulting in 85% of KCl shoot production. Furthermore, KOH activation was found to break the crystalline structure of glauconite and K-feldspar during co-pyrolysis with coffee husk, increasing the total content and available K in soil. The study suggests that glauconite has limited agronomic efficiency and does not release K in the short term. Therefore, co-pyrolysis of glauconite with K-rich organic materials and KOH can increase the solubility of K from silicates, thereby increasing its fertilizer potential.