Protassium+® Sulfate of Potash (SOP) Brings More Potatoes to the Table

As potato growers continue to seek ways to reduce farm expenses while increasing production, it’s important to identify the products and practices that can most efficiently increase crop yields and quality.

Compass Minerals conducted multiple potassium fertilizer field trials in Grant County, Washington, to determine the impact of sulfate of potash (SOP) and muriate of potash (MOP) on potato yield.

Trial results demonstrated a substantial yield advantage when applying 100% Protassium+ SOP.

All of our trials investigated the impact on potato yield when applying 100% SOP vs. 100% MOP, and were replicated four (4) times. Our most recent trial also included two SOP and MOP blends. Applications were soil-applied at planting.

Five site-years of trial data demonstrate a 16+% yield advantage when fertilizing potatoes with 100% Protassium+ SOP compared with 100% MOP as the potassium source.

Our trial also quantified our prior findings that applying blends of SOP + MOP outyield applications of 100% MOP, yet yield less than applications of 100% SOP.


The results of the field trials clearly show that choosing Protassium+ SOP as a potassium source contributes to higher potato yields for growers.

Protassium+ premium sulfate of potash provides high potassium, which plays a critical role in water regulation and translocation of sugars within the plant. It also delivers plant-available sulfate-sulfur, which is required for protein synthesis and plant growth. Protassium+ SOP has the lowest salt Index per unit of K2O when compared with other soil-applied, dry potassium fertilizers and contains less than 1% chloride, making it the safer potassium fertilizer choice for potatoes.

Learn more about how Protassium+ SOP compares with other potassium fertilizers.