Polyhalite as a Potassium Source for Fertilization of Ratoon Cane in a Cerrado Oxisol

Potassium (K) is the nutrient most required by sugarcane crops and is predominantly supplied through potassium chloride (KCl). However, as KCl production is highly concentrated in a few countries, Brazil—the world’s largest sugarcane producer—relies heavily on imported K fertilizers. In this context, identifying alternative sources, even if also imported, is strategic to diversify supply and reduce the risks associated with dependence on a single product. This study evaluated the performance of polyhalite, a natural multinutrient mineral, compared with KCl, as an alternative fertilizer for ratoon cane (CTC 4 variety) grown in a clay-textured Oxisol in Jataí, Brazil. A two-year field experiment was conducted evaluating four treatments: control (without K fertilization), KCl, polyhalite, and a 25/75 polyhalite + KCl blend. Potassium fertilization increased culm yield by about 38–61% compared with the unfertilized control. In addition, the association of polyhalite + KCl promoted greater plant height compared to the treatment without K fertilization and, when comparing the K sources applied alone, polyhalite promoted a larger culm diameter and a higher leaf S content than KCl. These results demonstrate the agronomic advantages of polyhalite and its blends for sugarcane fertilization, which reiterates their potential as efficient and sustainable alternatives to KCl and as part of a broader strategy for fertilizer-source diversification.