Getting more out of your MOP with Polysulphate® in row crop systems.

The progress of agriculture is rooted in the principle of producing more with less. Muriate of Potash (MOP or KCl) has long been the standard potassium (K) source in many production systems. Yet despite the availability of alternatives like potassium sulphate (SOP), MOP has remained the dominant (K) source due to cost and availability, while SOP has generally remained a secondary option. Polysulphate supplies K, in the sulfate form, with additional valuable secondary nutrients.

In 2024, ICL conducted a series of field experiments across the Southern U.S. in corn, cotton, rice, and sugarcane to evaluate alternative potassium strategies. The goal was to meet the crop’s sulfur requirements by applying Polysulphate while also diversifying the potassium source. This was achieved by blending Polysulphate, applied at 200 lbs./A, with MOP, reducing the MOP rate by 50-70%.

At 200 lbs/A, Polysulphate supplies approximately 28 lbs of K₂O, 38 lbs of sulfur (S), 24 lbs of calcium (Ca), and 7.2 lbs of magnesium (Mg). In comparison, 200 lbs/A of MOP supplies 120 lbs of K₂O and 94 lbs of chloride (Cl⁻). By reducing the MOP rate by 50%, chloride input is also cut in half—from 94 lbs/A down to 47 lbs/A—while Polysulphate offsets the potassium reduction and adds valuable secondary nutrients.

Corn Trial – Cedar Hill, TN

• Objective: Evaluate the impact of reducing MOP by 50% and replacing it with Polysulphate on corn yield and test weight.
• Fertilizers used: Foliar: Nova FLOW® (5-10-20-11S-9Mg-0.5B) and PULSE® (0-6-4-1.3S-1Mg-0.5Co- 10Mo-6Zn)
• Key Results: Addition of Polysulphate while reducing MOP improved both test weight and yield. Polysulphate without MOP and adding foliar Nova FLOW and Nova PULSE increased corn yield by 6% (10 bu/A) over GSP.

Table 1. 2024 Corn trial Cedar Hill, TN – Soil test K: 115 ppm (230 lb./A)

Cotton Trial – Tifton, GA

• Objective: Evaluate cotton yield with Polysulphate and reduced MOP, combined with starter and foliar fertilizers.
• Fertilizers used:
  • Starter: Agrolution pHLow® (11-45-11-2Zn, 6 lbs./A) and BIOZ® Diamond (10-0-1)
  • Foliar: Nova FLOW® (5-10-20-11S-9Mg-0.5B, 3 lbs./A) and PULSE® (0-6-4-1.3S-1Mg-0.5Co- 10Mo-6Zn, 3 lbs./A)
• Key Results: Treatments with Polysulphate (and 50% less MOP) performed similarly to the grower standard practice (GSP).

Table 2. 2024 Cotton trial Tifton, GA – Soil test K: 45 ppm (90 lbs./A), EB- Early bloom

Rice Trial – Memphis, TN & Campbell, MO

• Objective: Evaluate rice response to reduced MOP and added Polysulphate across two locations.
• Key Results: Across both locations yield increased with reduced MOP and added Polysulphate by 7 to 11 bu/A over the GSP.
  • TN: (10 ppm soil S and 186 ppm soil K): Yield increased with reduced MOP and added Polysulphate.
  • MO: (20 ppm soil S and 218 ppm soil K): Similar yield to GSP with Polysulphate addition.
• Differences may be due to initial soil S and K levels (rice is sensitive to high S levels) and variety differences:
  • TN: Variety PVL03
  •  MO: Variety CL118
• To optimize both potassium and sulfur application, we are evaluating lower rates of Polysulphate in rice systems. Growers in Southeast Missouri (SEMO) applying 100–150 lbs/A of Polysulphate have reported yield increases comparable to those observed in our Tennessee trial site of 10 to 20 bu/A. Based on these results, we have updated our recommendation for rice to a Polysulphate application rate of 100–150 lbs/A. These rates will be further evaluated in our new trials plan.

Table 3. 2024 Rice trial, Memphis, TN and Campbell, MO. – Soil test K: TN 186 ppm (372 lbs./A); MO 218 ppm (436 lbs./A)

Sugar Cane Trial – Houma, LA

• Objective: Evaluate the impact of reducing MOP of the grower standard and replacing it with Polysulphate on sugarcane yield.
• Key Results:
  • Highest sugar and yield was achieved with reduced MOP at 50% (100 lbs./A) and 70% (140 lbs./A) in combination with 200 lbs./A of Polysulphate.
  • Polysulphate proves to be beneficial both as a standalone and in combination with MOP.
  • Polysulphate at 200 lbs/A (28 lbs./A K₂O) alone produced similar yield to MOP applied at 200 lbs/A (120 lbs./A K₂O).
  • Polysulphate was shown to be a more efficient K source compared to MOP.

Table 4. 2024 Sugarcane trial at Spanish Trail, Houma, LA (Variety L 01-299) – Soil test: pH 6.4, K 102 ppm (204 lbs./A)

3 things to know about blending Polysulphate with MOP

1. Yield stability or improvement across crops: Across corn, cotton, rice, and sugarcane, reducing MOP and supplementing with Polysulphate maintained or increased yield compared to grower standard practices.
2. Enhanced Nutrient Efficiency: Polysulphate supplies secondary nutrients (S, Ca, Mg) and matches or increases yield with lower total potassium applied.
3. Reduced Chloride Input: Replacing 50% MOP with Polysulphate reduces chloride by half, which can improve crop health, particularly in
   chloride sensitive crops and soils.

Final Word

Blending Polysulphate with reduced MOP maintains or improves crop yield across multiple cropping systems. It enhances nutrient efficiency and reduces chloride load, making it a more efficient and sustainable potassium source, while also supplying essential nutrients like calcium (Ca), magnesium (Mg), and sulfur (S). Soil test levels for potassium and sulfur, as well as crop variety, should guide the appropriate application rate.