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Copy link Getting More Out of Your MOP with Polysulphate® in Row Crop Systems
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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.
Field Trial Overview
In 2024, ICL conducted a series of field experiments across the Southern U.S. in corn, 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 224 kg/ha, with MOP, reducing the MOP rate by 50-70%.
At 224 kg/ha, Polysulphate supplies approximately 31 kg K₂O/ha, 43 kg S/ha, 27 kg Ca/ha, and 8 kg Mg/ha. In comparison, 224 kg/ha of MOP supplies 135 kg K₂O/ha and 105 kg Cl⁻/ha. By reducing the MOP rate by 50%, chloride input is also cut in half, from 105 kg Cl⁻/ha to 53 kg Cl⁻/ha, while Polysulphate offsets the potassium reduction and adds valuable secondary nutrients.
Maize 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% (0.63 t/ha) over GSP.
| Treatment Desription | K₂O Rate (kg/ha) | Test Weight (kg/hL) | Yield (t/ha) |
|---|---|---|---|
| Grower Standard Practice (GSP) (0-0-60 MOP, 149 kg/ha) | 89.7 | 76.0 | 10.23 |
| Reduced MOP + Polysulphate (0-0-14, 75 kg/ha + 224 kg/ha) | 76.2 | 76.3 | 10.36 |
| Polysulphate (0-0-14, 224 kg/ha) | 31.4 | 76.7 | 10.61 |
| Polysulphate (0-0-14, 224 kg/ha) + Nova FLOW (3.36 kg/ha) + Nova PULSE (0.56 kg/ha) | 31.4 | 76.8 | 10.86 |
Table 1. 2024 Maize trial Cedar Hill, TN – Soil test K: 115 ppm (258 kg/ha)
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 0.35 to 0.55 t/ha 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 optimise both potassium and sulphur application, we are evaluating lower rates of Polysulphate in rice systems. Growers in Southeast Missouri (SEMO) applying 112-168 kg/ha of Polysulphate have reported yield increases comparable to those observed at our Tennessee trial site of 0.5-1.0 t/ha. Based on these results, we have updated our recommendation for rice to a Polysulphate application rate of 112-168 kg/ha. These rates will be further evaluated in our upcoming trial programme.
| Treatment Description | K₂O Rate (kg/ha) | TN Yield (t/ha) | MO Yield (t/ha) | Avg Yield (t/ha) |
|---|---|---|---|---|
| MOP (224 kg/ha) | 100.9 | 5.90 | 9.02 | 7.46 |
| Polysulphate (224 kg/ha) | 31.4 | 6.70 | 8.87 | 7.81 |
| Reduced MOP (84 kg/ha) + Polysulphate (224 kg/ha) | 84.0 | 7.21 | 8.82 | 8.01 |
Table 3. 2024 Rice trial, Memphis, TN and Campbell, MO. – Soil test K: TN 186 ppm (417 kg/ha); MO 218 ppm (489 kg/ha)
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 content and yield were achieved with reduced MOP rates of 112 kg/ha (50% reduction) and 157 kg/ha (70% reduction), in combination with 224 kg/ha of Polysulphate.
- Polysulphate proved beneficial both as a standalone potassium source and when combined with MOP.
- Polysulphate applied at 224 kg/ha (supplying approximately 31 kg K₂O/ha) produced a similar yield to MOP applied at 224 kg/ha (supplying approximately 135 kg K₂O/ha).
- Polysulphate was shown to be a more efficient potassium source than MOP.
| Treatment Description | K₂O Rate (kg/ha) | Cane Yield (t/ha) | Sugar Yield (t/ha) | Total Recoverable Sugar (kg/t) |
|---|---|---|---|---|
| Control (unfertilised) | 0 | 89.7 | 11.2 | 124.5 |
| MOP (224 kg/ha) | 134.5 | 94.2 | 12.1 | 128.5 |
| Polysulphate (224 kg/ha) | 31.4 | 96.4 | 12.3 | 127.5 |
| Reduced MOP (112 kg/ha) + Polysulphate (224 kg/ha) | 98.6 | 96.4 | 12.4 | 128.0 |
| Reduced MOP (157 kg/ha) + Polysulphate (224 kg/ha) | 125.5 | 100.9 | 12.7 | 125.0 |
| MOP (224 kg/ha) + Polysulphate (224 kg/ha) | 165.9 | 94.2 | 11.6 | 122.5 |
Table 4. 2024 Sugarcane trial at Spanish Trail, Houma, LA (Variety L 01-299) – Soil test: pH 6.4, K 102 ppm (229 kg/ha)
3 things to know about blending Polysulphate with MOP
- 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.
- Enhanced Nutrient Efficiency: Polysulphate supplies secondary nutrients (S, Ca, Mg) and matches or increases yield with lower total potassium applied.
- 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.
