Crop Nutrition

Soybean Sensitivity to Chloride – Should You Be Concerned?

Robert Mullen, Ph.D.

Robert Mullen

Robert Mullen, Ph.D.

Nutrien

Director of Agronomy

To say Dr. Robert Mullen is passionate about agriculture would be an understatement. He holds a Bachelor of Science degree in ag business from Cameron University, along with a Master of Science degree in plant and soil science and a Ph.D. in soil science from Oklahoma State University. In addition, Dr. Mullen has been published in a variety of scientific and trade journals. But it’s not just his academic accomplishments that make him unique. It’s his unwavering ability to take complex data and — in simple terms — explain how it impacts a farmer’s bottom line. Dr. Mullen delivers the kind of insightful observations that can lead to a more profitable business. As a leading agronomy expert, Dr. Mullen has a goal to further educate farmers on best management practices that improve their yields and maximize their return on investment.

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A recent article published by the University of Minnesota raises concerns of soybean sensitivity to chloride from muriate of potash applications. We will discuss the implications of this article and raise questions that remain unanswered. Potential beneficial and harmful effects of the nutrient chloride have received much attention over the years. Yes, chloride is also an essential plant nutrient. 

The focus of the University of Minnesota article (available here) is that many of the soybean varieties utilized at more northern latitudes are classified as chloride “includers”. Thus, they can be susceptible to negative impacts if excess chloride is applied (excess is the key to this discussion). One thing to note from this particular article is that soil test potassium level is critical in determining the potential negative impacts of chloride. The authors state that if soil test potassium level is low, potassium should be applied regardless of source.

The natural first, and maybe most important, question is – how much chloride is considered excessive?  If one follows University of Minnesota recommendations, the maximum amount of chloride recommended to soybeans would be 90 pounds per acre (assuming muriate of potash as the potassium source and a desired application rate of 120 pounds of K2O per acre). The “excessive” level determined from the research discussed was 500 pounds of chloride per acre. A rate unlikely to be approached under normal agronomic conditions.

What other questions should be considered? What was the timing of the high potassium chloride and calcium chloride rates? Were those products applied in the spring or in the fall? Would the chloride be leached out of the root zone if it was applied in the fall? Chloride persistence in the root zone would be more likely with lower rainfall the further west one moves. Hopefully, the specific details of the experiments will be shared at a future date.

Purdue University has also provided a “response” to the article published by University of Minnesota.  The Purdue article is available here.

So, what do you do with this information? 

  • Continue to rely upon soil test information/trends to make potassium decisions. Typical agronomic rates of muriate of potash are not considered to be of concern.
  • Avoid large application rates of muriate of potash prior to soybeans (the University of Minnesota document recommends staying less than 100 pounds of chloride per acre – at least I think that is what they meant in the document) especially on coarser textured soils.
  • Fall timing might be a better option for higher rates of muriate of potash prior to soybeans.