Comparative study of potassium rates and sources on potato yield and quality in Florida

Sandy soils are prone to potassium (K) leaching; therefore, developing guidelines for the optimum K application rate and fertilizer source is necessary. This research aimed to evaluate the optimum K fertilizer rates and identify the best K fertilizer sources for potato (Solanum tuberosum L.) production, considering the impacts of insufficient or excessive fertilization on potato yield and tuber quality. The experiment was carried out on Florida sandy soil in a randomized complete block design with four replications and nine treatments, a combination of three K sources (potassium sulfate [K₂SO₄], potassium chloride [KCl], and potassium magnesium sulfate [K₂Mg₂(SO₄)₃]) and three rates (224, 280, and 336 kg K₂O ha⁻¹). Potato tuber yield was affected by different K fertilizer sources. Applying KCl resulted in a 10.3% and 9.0% increase in marketable and total tuber yield, respectively, compared to K₂SO₄. However, KCl application resulted in significant tuber quality deterioration regarding lower tuber-specific gravity. Yield and quality of potatoes were improved with the application of K₂Mg₂(SO₄)₃. No significant increase in tuber yield with increasing K rates from 224 to 336 kg K₂O ha⁻¹. The highest K rate (336 kg K₂O ha⁻¹) resulted in a 10-fold and threefold drop in tuber-specific gravity values in 2022 and 2023, respectively, compared to 224 kg K₂O ha⁻¹. These results suggest that K application rate and fertilizer source must be optimized to balance potato yield and tuber quality.