Sugarcane response to polyhalite fertilizer in Brazilian Oxisols

Polyhalite (PYH), (K2SO4·MgSO4·2CaSO4·2H2O), contains four nutrients of great importance to sugarcane (Saccharum spp.), but has lower water solubility than traditional K fertilizers. Two studies were conducted to determine if PYH fertilizer (11.6% K) promoted sugarcane response comparable to other K fertilizers on highly weathered, acidic Oxisol soils in Brazil. A pot study compared PYH with potassium chloride (KCl, 50% K) and potassium sulfate (K2SO4, 40% K and 17% S), both amended to the same Ca, Mg, and S contents, applied at five rates ranging from 0 to 166 kg K ha−1 in limed and unlimed soil. A field study evaluated PYH with KCl applied in a 5–30–10 blend at planting followed by sidedress applications of K as PYH or KCl in the establishment year and two ratoon crops. In the pot study, there were minimal effects of fertilizer source and application rate on early growth in sugarcane while liming was detrimental. Uptake of K in the biomass was linear and similar among fertilizer sources. PYH increased S uptake and soil tests compared to KCl and K2SO4. In the field study, KCl and PYH had similar sugarcane yield and quality with K uptake in both exceeding K applied and PYH increased S uptake and soil test SO4–S. These studies confirm nutrient release from PYH to sugarcane was adequate and comparable to KCl and K2SO4, with some effect of PYH on nutrient uptake and soil test that did not affect sugarcane yield or quality.