5 Ways to harness the power of potassium

These five guidelines will ensure farmers get the most return on investment out of their K applications.

Underneath corn canopy

Plants require potassium (K) because it supports stalk health, balances anions such as nitrate and sulfate, manages plant water relations, and activates enzymes that ensure healthy growth.

"Most soils need additional K," says Jeff Vetsch, a University of Minnesota (U of M) soil fertility researcher, "but there are soil differences.

"Certain soil minerals or, parent material, release more K through weathering than other soils. Also, some clays can tie up K between the clay layers. Coarse-textured sands need less K as it can leach and the critical soil test K values are lower than those on medium- and fine-textured soil."

He adds that corn and forages take up more than 100 pounds per acre and up to 200 pounds per acre of K. Most K stays in the forage, while grain removal of K is relatively low in corn and greater in soybeans.

He says these five guidelines will ensure farmers get the most return on investment out of their K applications.

1. Don't overapply phosphorus.

"Farmers sometimes apply too much phosphorus (P) to their fields, and annual crop removal builds soil test P on neutral and acid soils," he says. "I'd rather see these excess P fertilizer dollars spent on K, especially in the Upper Midwest, because the ROI potential is greater."

2. Test your soil.

"Sample soil in the spring or fall at the same time each year," Vetsch says. "Don't vary the test timing because it can affect soil test K results, probably more so than other nutrients."

He says these factors can impact soil test results:

  • Clay mineralogy.
  • Soil moisture content at sampling.
  • Crop residue, if soil testing in the fall.

"Crop residues hold a lot of K and it takes a while for it to leach back into the soil," he says. "So, if you sample in early fall, you may get lower values than when testing in spring."

3. Use the correct soil test.

To keep soil test results as accurate as possible, use the right soil test and extractant for your region or state. Vetsch says universal extractants such as Mehlich III may not be calibrated to your state's K fertilizer guidelines.

4. Consider applying K yearly.

"It may be advantageous to apply K annually on coarse-textured soils," he says. "This applies through-out the Corn Belt and likely on low-CEC soils across the country."

5. Pursue higher K applications, where applicable.

Vetsch says U of M research has shown significant return on investment with K application rates being greater than crop removal rates for corn and soybeans, especially on medium testing soils — approximately 100 to 150 parts per million using the ammonium acetate test. Proper K application may vary, depending on the situation.

"Some crops, especially corn, may respond to band applications of K," he says, "but recent U of M research shows the yield benefit is relatively small and may not pay for the additional application costs compared to broadcast applications. But, if you're banding in a strip-till-age system, keep doing it as it reduces K stratification. I've also seen yield responses to band applications over broadcast in reduced-till and no-till systems."

K doesn't have the environmental concerns P and N do, but poorly managed potassium still affects ROI, so proper application is key to getting the most from the fertilizer, Vetsch adds.

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