Polyhalite as an alternative potassium fertilizer for sweetpotatoes

Abstract

Polyhalite is a mineral that contains a significant source of potassium (K). Muriate of potash (MOP) is a widely used, well-characterized, and available source of K fertilizer. This study evaluated polyhalite as a source of K fertilizer compared to the more commonly used MOP by measuring yields, nutrient uptake, and soil K in Covington sweetpotato (Ipomoea batatas) production. MOP and polyhalite were applied at increasing rates (32.5, 62, 126, and 188 K₂O ha⁻¹) to determine optimum application rates and comparative yield responses between sources. Yield regression showed a quadratic response to fertilizer application regardless of source, with a peak marketable yield of 37 t ha⁻¹ at approximately 100 kg K₂O ha⁻¹. Fertilizer rates above 100 kg K₂O ha⁻¹ resulted in a decline in yields. MOP initially released a higher amount of K than polyhalite, highlighting differences in early-season K solubility. There were no differences in root or leaf tissue concentrations of K, calcium (Ca), and magnesium (Mg) in response to treatments; however, polyhalite treatments did result in increased sulfur storage in leaf and root tissue. These findings suggest that polyhalite can be used as an alternative source of K with comparable responses to the MOP in sweetpotatoes, and that polyhalite can be used as a slow-release fertilizer or source of sulfur.