Potential of Polyhalite As a Multi-Nutrient Fertilizer Source for Sugarcane Production.

Multi-nutrient fertilizers offer numerous potential benefits for crop production such as improved yields and better nutrient use efficiency due to synergies arising from different nutrient components. This study characterized yield and quality responses of sugarcane (Saccharum spp.)  to polyhalite (a potassium, calcium magnesium sulfate fertilizer; K₂Ca₂Mg(SO₄)₄•2H₂O) and two other K fertilizers [potassium chloride - KCl, and potassium sulfate - K₂SO₄] on a calcareous soil (Hidalgo sandy clay loam; pH 8.1) in south Texas. Potassium rates were: 0, 50, 100, 150, and 250 kg·ha^-1. At planting, phosphorus (11-37-0) was side-dressed at 39 Kg P₂O₅ ha^-1; nitrogen (N; urea ammonium nitrate; 32% N) was applied with irrigation at 162 kgN·ha^-1 in 2 split applications. Potassium fertilization had a significant effect on stalk weight, cane yields and sucrose content. Plant cane yields were 7.7% higher in K fertilized plots compared to control plots. Plots receiving K₂SO₄ had slightly higher yields (102 Mg·ha^-1) than those fertilized with polyhalite (97 Mg·ha^-1) or KCl (98 Mg·ha^-1) but there were no significant differences among K sources. Among the yield components measured, only stalk diameter and stalk weight were significantly affected by K fertilization. Average sugar yield (Mg·ha^-1; product of cane yield and sucrose concentration) for K treated plots was 22% higher than controls but similar among K sources. Plots fertilized with K₂SO₄ also ranked slightly higher for brix, stalk diameter, stalk weight and millable stalks per ha; however, differences among fertilizer sources were not significant. Fertilization rate effects were not consistent; the highest cane and sugar yields with KCl were obtained at the 150 kg·ha^-1 rate whereas for K₂SO₄ and polyhalite, this was achieved at the 100 kg·ha^-1 rate.