Enough with the Potassium, Already!

Since the chemical age of agriculture that began in the 1960s, potassium chloride (KCl) - a common salt known as potash - has been widely used as a major fertilizer in the Corn Belt.

Now, University of Illinois soil scientists are raising serious concerns with agriculture's 50-year potassium habit with research showing that testing soils for potassium is of no value for predicting its availability and that KCl fertilization seldom pays.

The findings came from a field study that involved four years of biweekly sampling for K testing with or without air-drying. Test values fluctuated drastically, did not differentiate soil K buildup from depletion, and increased even in the complete absence of K fertilization.

Explaining the increase, researcher Saeed Khan pointed out that for a 200-bushel corn crop, "about 46 pounds of potassium is removed in the grain, whereas the residues return 180 pounds of potassium to the soil—three times more than the next corn crop needs and all readily available."

Khan emphasized the overwhelming abundance of soil potassium, noting that soil test levels have increased over time where corn has been grown continuously. "In 1955 the K test was 216 pounds per acre for the check plot where no potassium has ever been added. In 2005, it was 360."

A similar trend has been seen throughout the world in numerous studies with soils under grain production.

KCl fertilization has long been promoted as a prerequisite for high nutritional value for food and feed. Yet, researchers have found that the qualitative effects were predominantly detrimental, based on a survey of more than 1,400 field trials reported in the scientific literature.

"Potassium depresses calcium and magnesium, which are beneficial minerals for any living system. This can lead to grass tetany or milk fever in livestock, but the problems don't stop there," Khan pointed out.

"Low-calcium diets can also trigger human diseases such as osteoporosis, rickets, and colon cancer. Another major health concern arises from the chloride in KCl, which mobilizes cadmium in the soil and promotes accumulation of this heavy metal in potato and cereal grain. This contaminates many common foods we eat—bread, potatoes, potato chips, French fries—and some we drink, such as beer. I'm reminded of a recent clinical study that links cadmium intake to an increased risk of breast cancer."

The Illinois researchers see no value in soil testing for exchangeable potassium and instead recommend that producers periodically carry out their own strip trials to evaluate whether potassium fertilization is needed. Based on published research cited in their paper, they prefer the use of potassium sulfate, not KCl.

Sources: University of Illinois College of Agricultural, Consumer and Environmental Sciences;
"The potassium paradox: Implications for soil fertility, crop production and human health" by Saeed Khan, Richard Mulvaney, and Timothy Ellsworth posted October 10, 2013 by Renewable Agriculture and Food Systems.

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