Potassium: The Forgotten Macronutrient


Nitrogen and phosphorus get all the glory when it comes to the macronutrients. But there are two others in the NPKS mix, you know. The third most important nutrient, potassium, often gets thrown by the wayside and only seems to come up when there is a market discussion on Potash Corp or Russia’s Uralkali. There should be more emphasis put into understanding the importance and benefits of potassium fertilization, in my opinion, so let’s explore the role of this nutrient.

Potassium (fertilizer source generally Potash, or KCl, for potassium chloride) is what keeps the plant in four-wheel drive, moving other nutrients, sugars, water through the plant, ensuring those other important nutrients, nitrogen and phosphorous, get to where they need to be. Some research has even shown an increase in nitrogen use efficiency when adequate potassium is available! To top it off potassium can play a big role in ensuring pods/heads are filling — increasing crop quality, especially in cereals. Next, it is very key in maintaining turgor pressure in plants…like a naturally occurring Viagra, if you will. If you have ever seen a crop on a hot day look droopy and “sad” as I have heard it called many times, that is what a lack of turgor pressure looks like in a plant. So droopy plants can be an early sign of a lack of potassium; standability can be an issue in deficient plants. Water is a driver in turgor pressure, but also in a plant’s ability to handle heat, drought and disease pressure.

Read More: Check out more agronomy topics by Shane Thomas here

“But my soil has a lot of potassium!” you say.  This statement is very true in many situations across much of Western Canada, but it is not that simple. The chemistry and intermingling of different nutrients, organic matter, organisms and more have a large effect on nutrient availability in our soil, and potassium is no exception to this. The levels of other cations in soil can have a huge impact on what plants can uptake vs. what is there, with magnesium being the culprit across many different soil zones when talking about lack of potassium uptake. If your soil has a much higher level of magnesium than potassium, the magnesium essentially suffocates the roots, making it tougher for the plant to uptake potassium.

If you are looking at soil tests ensure you check out base saturation levels and K/Mg ratios. If your base saturation of potassium is <3% or your K/Mg ratio is <0.25 then there could be a struggle getting the right amount of potassium taken up by the crop.

In many of our crops the uptake of potassium is equal to the amount of nitrogen uptake, as well, so keep that in mind when you are planning fertilizer applications for the 2014 season and beyond.

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