No-Tillers May Want to Re-Examine Soil Test ‘K’, Application Habits

Study finds little or no correlation between soil-test potassium levels and higher yields, with crop residue and deeper soil reserves providing more than enough of the nutrient.

No-tillers looking for a way to cut fertility costs might want to review what they’re spending on potash (KCI) and other potassium (K) fertilizers, because in many soil types and situations there’s a good chance you’re wasting your money, says Saeed Khan.

After several years of intense soil sampling work at different research sites and poring over thousands of peer-reviewed studies in the U.S. and abroad, the former soil scientist at the University of Illinois completed his PhD thesis paper, The Potassium Paradox: Implications for Soil Fertility, Crop Production and Human Health. It concludes that plant residue, along with what’s available in the soil profile, typically produces enough K to raise grain crops.

Co-authored by Richard Mulvaney and Timothy Ellsworth, Khan’s research found little or no correlation between K applications and yields, as well as evidence that university agronomists have known this for decades, but haven’t widely publicized it. Khan waited nearly a quarter century for his work to be published, which it eventually was by Oxford Peer Review Journal.

“Potassium is the most abundant macronutrient in the soil. But it’s the most overused unnecessarily,” Khan told attendees at the National No-Tillage Conference. “Public universities produce recommendations and say there’s a lot of research data, but there’s no science behind it.”

Always There

K is completely different from phosphorus (P) and nitrogen (N) because it’s always in inorganic form and water soluble, Khan says. Soil potassium exists in mineral, exchangeable and non-exchangeable forms, but it’s only the exchangeable K…

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John dobberstein2

John Dobberstein

John Dobberstein is senior editor of No-Till Farmer magazine and the e-newsletter Dryland No-TillerHe previously covered agriculture for the Tulsa World and worked for daily newspapers in Chicago, Milwaukee and St. Joseph, Mich. He graduated with a B.A. in journalism and political science from Central Michigan University.

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