Researchers from the University of Illinois have made a bold claim regarding soil fertility. The research concluded that soil tests for potassium chloride (KCI) are of no value when predicting soil K availability and suggests KCI fertilization may not be as beneficial as once thought to plant growth. In fact, the study found the addition of KCI may actually limit yields in some cases.
The study was conducted over four years, sampling twice each week for soil K. Test results varied wildly and did not differentiate between soil K buildup and soil K depletion. Samples without KCI applications showed increasing amounts of soil K over time while some fertilized plots declined.
The irony, according to U of I researcher Richard Mulvaney, is that before 1960 there was very little usage of KCl fertilizer. He explained, "A hundred years ago, U of I researcher Cyril Hopkins saw little need for Illinois farmers to fertilize their fields with potassium," Mulvaney said. "Hopkins promoted the Illinois System of Permanent Fertility, which relied on legume rotations, rock phosphate, and limestone. There was no potash in that system. He realized that Midwest soils are well supplied with K. And it's still true of the more productive soils around the globe. Potassium is one of the most abundant elements in the earth's crust and is more readily available than nitrogen, phosphorus, or sulfur. Farmers have been taught to think that fertilizers are the source of soil fertility-that the soil is basically an inert rooting medium that supports the plant."
U of I researcher Saeed Khan recounts the story of a Pakistani man making mud walls from a mixture of clay and KCI fertilizer. Kahn states the man was using the same bag of fertilizer that farmers had used to fertilize soils. The introduction of KCI to the clay made the mud strong and hard, much like cement. Khan then realized that KCI changes the soils' physical properties which can inhibit plant growth and discourage root systems.
The study recommends using potassium sulfate, not potassium chloride as the sulfate will work against KCI's tendency to solidify soils. The study suggests growers rethink potassium chloride use and recommends growers carry out their own strip trials to get a handle on their individual KCI needs in the soil.
This research implies potash may not be as good for the soil as once thought, nor as beneficial for plant growth and yield. Click to read the full report from the University of Illinois titled "The Potassium Paradox: Implications for soil fertility, crop production and human health".