The Potential of Polyhalite As a Multi-Nutrient Fertilizer for Sugarcane in Brazil.

Currently, Brazilian sugarcane production uses different single nutrient fertilizer sources to meet potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S) requirements, increasing production cost. To overcome this constraint, this study aimed to evaluate polyhalite (POLY4) as a multi-nutrient source on sugarcane yield and soil K, Ca, Mg and content changes, compared to combined applications of a commercial K fertilizer (potassium chloride – MOP) and a Ca, S source (gypsum – GYP). The field experiment was conducted in 2014-2015 with sugarcane (Saccharum ssp. cultivar. CV 7870) on a Quartzipsamment in Agudos, Brazil, arranged in a randomized block design with K, Ca, Mg, S sources; five dosages of POLY4 (0, 250, 500, 750, and 1000 kg ha^–1) and a fixed MOP dosage (175 kg ha^–1) combined with 5 rates of GYP (0, 317, 633, 950, and 1266 kg ha^–1), simulating Ca and S POLY4 dosages evaluated. Our results demonstrated that sugarcane yields were influenced by both, source and dosage (p<0.05). According to source, higher yields were achieved from POLY4 applications (average 113.3 t/ha) compared to MOP-GYP (average 106.8 t/ha), probably due to the nutrient content of the fertilizer source. Regards to dosage, 750 kg POLY ha^-1, corresponded to the farmer’s recommendation based on 105 kg K₂O ha^-1, showed the highest yield (120.5 t ha^-1). These results are correspond with soil K content (p<0.05) post-harvest, mainly in the 0- to 10-cm layer, where farmer’s recommendation applied by POLY4 provided higher soil K content (70.4 mg kg^-1) compared to similar dosage of MOP-GYP (54.7 mg kg^-1). Soil Ca, Mg and S contents were only influenced by dosage in the three soil layer assessed, even though these elements are present in the fertilizers evaluated. The study demonstrated that Polyhalite can enhance soil K content and improve yield in commercial field conditions.