Added Benefits

Protassium+ increases tuber yield and quality

Published in the April 2015 Issue Published online: Apr 30, 2015 Fertilizer Dr. Samuel Essah, assistant professor, Colorado St
Viewed 2365 time(s)

Choosing the right source of potassium is critically important for producing optimum yields and crop quality. Without adequate potassium, tuber yields are reduced and smaller tubers are produced. My previous studies at Colorado State University have shown that the differences between various sources of potassium fertilizer can be expressed through delayed tuber development, increased external and internal tuber defects and reduction in tuber specific gravity.

Studies were conducted at Colorado State University at the San Luis Valley Research Center to evaluate the effect of Protassium+ and muriate of potash (MOP) as the source of potassium fertilizer on russet potato tuber yield and quality.

Protassium+, which is produced by Compass Minerals, is a premium, high-quality source of potassium with sulfate sulfur that provides superior crop nutrition and is virtually chloride-free. Protassium+ has the lowest salt index of all major sources of potassium. For this reason, it provides added flexibility in application timing without the risks of salt buildup that over-application or continued application of other potassium sources can pose. This is especially important when managing crops in high-saline soil environments or when irrigation water quality is poor.

Following is a review of some of the key findings:

  • Using Protassium+ as a potassium fertilizer source improved potato root and tuber development, as seen in the accompanying photos. This is critical in order to optimize plant health and vigor. The bigger and stronger the root system, the more efficiently the plant can get nutrients and water from the soil.
  • Using Protassium+ at a rate of 120 pounds of K2O per acre increased total tuber yield by 12 and 6 percent, respectively, when compared to the control and MOP fertilizer treatments, respectively.
  • The percentage of marketable tuber (>4 ounces) yield increased by 22 and 13 percent, respectively, when compared the control and MOP fertilizer source treatments .
  • The yield advantage observed for Protassium+ as a source of potassium fertilizer is due to the low salt index of Protassium+ compared to MOP.
  • Tuber external defects (growth cracks, knobs and misshapes) and tuber internal defects (hollow heart and brown center) were significantly reduced when Protassium+ was used as the source of potassium fertilizer compared to MOP.
  • In this study, using Protassium+ as the potassium source increased tuber specific gravity compared to MOP.

Data from these studies indicate that when Protassium+ is used as source of potassium fertilizer, the yield of marketable and premium size tubers increases significantly compared to the use of MOP as the source of potassium fertilizer. As observed in previous studies conducted at Colorado State University, tuber specific gravity was increased when Protassium+ was used as source of potassium fertilizer instead of MOP. Higher specific gravity also means less water in the harvested crop, which can lessen storage losses due to shrinkage significantly.

To learn more about Protassium+, visit

Dr. Samuel YC Essah is an associate professor of agronomy and horticulture at Colorado State University’s Department of Horticulture & Landscape Architecture. He is based at the San Luis Valley Research Center in Center, Colo.