Potassium: More than just a crop nutrient

Potassium has been referred to as the mother of all nutrients for the numerous benefits it provides plants.

“Potassium can influence the efficiency of many other nutrients in our crop production system such as water use efficiency, drought tolerance, stalk quality, standability and disease tolerance,” Pioneer field agronomist Troy Deutmeyer said.

Deutmeyer noted several field trials across the Corn Belt that show the impacts of both potassium and phosphorous on crops and optimum soil test range recommendations from those trials.

Iowa State University trials found year-to-year yield variability can be reduced by building up soil test potassium levels.

“Pioneer recommends for your soil test for potassium to generally be in that 200 to 250-plus parts per million range, that way we eliminate a lot of yield variability,” Deutmeyer said. “In the soil test initiative conducted by Pioneer, we took thousands of soil tests in our customers’ fields and found 60 percent of those fields had potassium levels below 160 ppm. That’s a long way from the 200 to 250 that we recommend to try to maintain the yields stability from year-to-year.”

Nitrogen Efficiency

Customers often ask Deutmeyer what they can do to improve their nitrogen use efficiency and better manage their nitrogen.

“A lot of times their questions refer to the form of nitrogen they’re using or the rate or timing or application method. One of the first things that I ask them is what their soil test potassium levels are,” Deutmeyer said.

He referred to a study conducted at Ohio State University comparing nitrogen rates, soil test potassium levels and corn yields.

Plots with low potassium levels at 80 ppm and 280 pounds per acre of nitrogen yielded 167 bushels per acre. Plots with potassium levels of 139 ppm and 180 pounds per acre of nitrogen applied yielded 211 bushels per acre.

“That 44-bushel advantage tells us they had a nitrogen use efficiency of 0.85 which is a very high level of ni- trogen use efficiency. That tells us that we can become very efficient with our nitrogen if we have adequate soil test levels,” Deutmeyer noted.

Like nitrogen, potassium levels have a similar maximum return on investment.

Pioneer conducted trials in 20 eastern Iowa fields and found the yield curve flattens out at potassium soil test levels of 300 ppm.

“We really don’t see a need to be above this. At about 250 ppm the curve in the trials really starts to flatten out. That’s why we are recommending around that 200 to 250 ppm range,” Deutmeyer said.

Yield Trends

Data from five years of Pioneer’s Intensively Managed Product Advancement Characterization and Training testing of corn across 133 locations found a 47-bushel difference between the low-yielding and high-yielding plots.

“There was a distinct trend as we move from high test to low soil