November 29, 2016
Potassium Fertilizers for Potatoes Go Head-to-Head
As a potato grower, you have a number of potash fertilizer sources to choose from. When you select a K fertilizer for your potato fields, consider more than just the percentage K value. Other characteristics of the fertilizer have an impact on your crop’s growth, yield, quality and storability.
In this evaluation, we will compare two K fertilizers most commonly used by potato growers:
- Sulfate of potash (SOP) or potassium sulfate
- Muriate of potash (MOP) or potassium chloride
To assess potassium thiosulfate and potassium magnesium sulfate (KMS) as well, watch this Spudman webinar on-demand.
Head-to-Head: Chloride Content
Although chloride is an essential nutrient for plants, an excess of chloride in the soil can block uptake of other essential nutrients, including nitrate, sulfate, phosphate and borate. SOP delivers less than 1% chloride, while MOP delivers 47%, a difference very evident in crop yields.
In 2012, Colorado State University conducted a study to evaluate the effects of fertilizer’s chloride content on potatoes. The study’s potato plants in the MOP treatment experienced a noticeable reduction in root growth and mass due to the fertilizer’s chloride content, as compared to the SOP treatment.
Head-to-Head: Potato Yield
SOP has been a part of numerous potato K fertilizer trials that have measured yield. The results are significant. On average, SOP plots yielded 5.1 MORE TONS of potatoes per acre than MOP plots.
Choosing SOP can have a significant impact on your farm’s profitability as well. In studies conducted over two years in Othello, Washington, the market value of the potatoes in the SOP treatment was $771/acre higher than the potatoes in the MOP treatment.
Head-to-Head: Potato Quality, Storage and Marketability
Trials have shown a number of ways that SOP improves potato quality as compared to MOP:
- SOP decreases the amount of external defects and growth cracks
- SOP decreases total sprouts and sprouting rate in storage
- SOP increases specific gravities
What do these quality assessments mean to you? Miller Research in Idaho calculated profitability of its 2012 potato trial comparing SOP with MOP. The SOP treatment generated $150/acre more in processing price than the MOP treatment.
Choose Protassium+TM as the Best K Fertilizer for Your Potatoes
The good news is that you have a choice in your potash fertilizer. Protassium+ premium sulfate of potash is field-proven to improve potato yield and quality, as compared to MOP. The only SOP fertilizer produced in North America, Protassium+ is available through a number of large and small fertilizer retailers in major potato-growing regions.
Consider the trial results and choose wisely. Ask your retailer for Protassium+, the ideal K fertilizer for potatoes. Read more about Protassium+ on potatoes here.
 Colorado State University, 2008-2011
 Colorado State University, 2008-2010
 Colorado State University, 2008-2010; Holland Agriculture Services, Washington