Over-Application of Potash Containing Chloride Can Hurt Soybean Yields

 

In past posts, I have discussed the potential issues which chloride (Cl) in potash can present for soybean production in Minnesota. The 2020 growing season was the fourth year of a long-term study funded by the Minnesota Soybean Research and Promotion council which compares potassium sulfate and potassium chloride (KCl) to calcium chloride (CaCl2) and a no fertilizer control. In addition, a study was established to determine the effects of a very high rate of Cl (500 pounds per acre) applied in the spring ahead of soybean.

 

 

Examination of the long-term data found small yield increases from potassium (K) fertilizer application regardless of source at three of the four locations. Yield increases were found for hard red spring wheat and corn at one location as well. Chloride was associated with a yield decrease of one bushel per acre at one of the four locations. The locations where yield was increased had low K soil test levels before application. This tells us that if K is needed, it should be applied regardless of source. The location in which yield was decreased by Cl had sufficient K in the soil as indicated by the soil test.

 

Trials where high rates of Cl was applied were done to look at a worse case scenario. Yield was decreased similarly when both potassium- and calcium-chloride was applied as a chloride source. At the Becker and Waseca sites, the yield reduction averaged four bushels per acre while there was an eighteen bushel per acre reduction at Morris, which was much drier during the 2020 growing season. Four varieties were planted at all three locations and all were affected the same.

 

 

The impact of Cl on soybean is not new and has been going on as long as soybean has been grown in the state. Most northern soybean varieties are considered “chloride includers,” which are susceptible to yield reduction from over-application of Cl. For growers in Minnesota, there is some concern that if too much Cl is applied directly ahead of the soybean crop, it could hurt soybean yield. While the exact tolerance is not known, the effect of Cl will be worse on poorly drained soils in years with low rainfall because Cl will not move out of the root zone.

 

In most cases, the yield reductions have been small. In our study, the three-year average yield at Waseca for soybean was 68 bushels per acre for the control and the average yield reduction was only one bushel per acre. However, in Morris, the high rate of Cl resulted in a yield decrease from 68 bushels to 50 bushels per acre, which would be a red flag to most growers. The fact is that a small reduction in yield will not be noticeable in the grand scheme of things, yet it is still a reduction in profitability while also paying for an unnecessary input. 

 

 

 

Potassium chloride is the most economical source of K we have to apply, so managing this issue comes down to applying K fertilizer only where it is needed. If K needs to be applied ahead of the soybean crop, keep the rate low. Our soybean fertilizer recommendations currently suggest no more than 100 pounds of potassium chloride be applied ahead of the soybean crop but the actual tolerable rate can vary from one field to another. However, we have encountered yield reductions in sandy soils, so no field is immune to these issues.

 

The research cited in this article was funded through research dollars provided by the Minnesota Soybean Research and Promotion Council.

 

Video: From Conventional to Regenerative: Will Groeneveld’s Journey Back to the Land

"You realize you've got a pretty finite number of years to do this. If you ever want to try something new, you better do it."

That mindset helped Will Groeneveld take a bold turn on his Alberta grain farm. A lifelong farmer, Will had never heard of regenerative agriculture until 2018, when he attended a seminar by Kevin Elmy that shifted his worldview. What began as curiosity quickly turned into a deep exploration of how biology—not just chemistry—shapes the health of our soils, crops and ecosystems.

In this video, Will candidly reflects on his family’s farming history, how the operation evolved from a traditional mixed farm to grain-only, and how the desire to improve the land pushed him to invite livestock back into the rotation—without owning a single cow.

Today, through creative partnerships and a commitment to the five principles of regenerative agriculture, Will is reintroducing diversity, building soil health and extending living roots in the ground for as much of the year as possible. Whether it’s through intercropping, zero tillage (which he’s practiced since the 1980s) or managing forage for visiting cattle, Will’s approach is a testament to continuous learning and a willingness to challenge old norms.

Will is a participant in the Regenerative Agriculture Lab (RAL), a social innovation process bringing together producers, researchers, retailers and others to co-create a resilient regenerative agriculture system in Alberta. His story highlights both the potential and humility required to farm with nature, not against it.