Potassium is one of the major nutrients required by all crops and is present in large quantities in the plant in the form of the cation K+. It plays a major role in achieving the maximum economic yield, as part of a balanced approach to crop nutrition, as well as influencing crop quality.Potassium is fundamental to many metabolic processes through the activation of a large number of enzymes required for chemical reactions. These include the synthesis of proteins and sugars required for plant growth. Only a relatively small proportion of the plant’s total potassium requirement is needed for this. The majority is required for the essential role of maintaining the water content of plant cells. These roles are discussed below. Many are interlinked.

In a publication brought to the public’s attention by news release from the University of Illinois several weeks ago, S.A. Khan, Richard Mulvaney and a colleague in the Department of Natural Resource and Environmental Sciences at the University of Illinois challenged a number of basic tenets of soil fertility, especially practices related to use of potassium (K) fertilizer. Citing hundreds of references and thousands of reported studies, they asserted that: K fertilizer is generally unnecessary in soils like most of those in Illinois; the soil test is not a reliable way to know how much K the soil will supply to a crop; K used as fertilizer can cause crops to have lower nutritional value; using K fertilizer can damage soil structure; and potassium chloride (KCl), which is the most commonly-used (and lowest-cost) K fertilizer material, is harmful to crops.

Fertilizer potassium is sometimes called “potash,” a term that comes from an early production technique where potassium was leached from wood ashes and concentrated by evaporating the leachate in large iron pots (“pot-ash”). This practice is no longer practical and is not environmentally sustainable. In food production, potassium is removed from the soil in harvested crops and must be replaced in order to maintain future crop growth.Over 350 million years ago, the huge Devonian Sea was slowly drying up in the area of Central Canada and northern U.S., leaving behind concentrated salts and minerals. This process continues today in places such as the Great Salt Lake and the Dead Sea. These ancient marine salts are now recovered and used in a variety of useful ways, with the majority being used as potassium fertilizer.

The UN says that in 2021, there will be around 690 million hungry people on the planet which accounts for 9 percent of the world’s population.  Global food security is especially of concern looking forward as the world population is expected to increase by about 35 percent over the next 40 years.Agricultural output will need to significantly increase to feed the growing population. As available land for expanding agriculture is scarce, increased food production will come only from increasing productivity per hectare, which will require optimum and balanced fertilizer use.Boosting crop yields can be achieved by the implementation of balanced fertilization practices, which will also ensure the preservation of soil fertility and the sustainability of the farm systems.

A recent article1 in Progressive Farmer over viewed research showing yield reductions attributed to potash (0-0-60, KCl or MOP) applications in corn (North Dakota) and soybean (Minnesota and Indiana). Although the mechanism(s) of “toxicity” were not known the yield reductions were large enough and frequent enough to be considered real. In the corn studies conducted by Dave Franzen at North Dakota State University the potash was applied in spring and detrimental rates were greater than 200 pounds per acre (120 lb K2O/acre). My (Casteel) soybean research in Indiana examined potash applied at or shortly after planting as a means of intensifying management. Rather, I observed 3 to 5 bu/ac yield reductions at this timing. Detrimental potash rates were 200 pounds per acre in some trials on prairie soils near West Lafayette and loam to coarse-textured soils near Wanatah in 2016 and 2017. I still observed yield reduction at a lower rate of 100 pounds per acre (60 lb K2O/acre) in 2019, but not in 2020 near LaCrosse. Dan Kaiser at the University of Minnesota also saw yield reductions from potash applications ahead of soybean (spring and even some fall timings), and suggested chloride might be the culprit. Even though these observations of yield reductions cannot be fully explained at this time, these reports have caused some farmers to evaluate their timing and rate of potash application.

We write ‘effects of potash deficiency’ rather than ‘symptoms of deficiency’, because so many of the negative effects of a shortage of available potash to crops are not clearly apparent, whereas ‘symptoms’ implies some visible effect. Of course severe deficiency has visible symptoms (Figure 1), but there can be many expensive negative impacts on the crop well before clear symptoms are seen.Because most crops contain considerably more potassium than nitrogen or other nutrients, it might be expected that potassium deficiency would be the most commonly seen. However the majority of the potassium in crop tissues is supplied from the reserves in the soil, with relatively little coming from freshly applied fertiliser – in contrast to nitrogen or sulphur. Problems begin to arise when these soil potassium reserves are insufficient, usually as indicated by soil analysis results of K Index 0 or 1.

Potassium (K) is an essential nutrient required by plants in large quantities. Potassium does not become part of the many complex organic molecules in the plant. It moves and performs many of its functions as a free ion, such as regulating plant water pressure, activating enzymes, balancing electrical charges, transporting sugars and starches, and more.1  Potassium fertilizers are mined from a variety of geologic potassium salt deposits around the world, some of the richest are in the Canadian province of Saskatchewan. The salts are processed to remove impurities and converted to a variety of fertilizers. Two of the most popular potassium fertilizers derived from these salt deposits are potassium chloride and potassium sulfate. The term “potash” is a general term that is often used to refer to a variety of potassium fertilizer salts or sometimes more specifically to potassium chloride, the most widely used potassium fertilizer. Potassium chloride is referred to as “muriate (meaning chloride) of potash” or MOP, while potassium sulfate is sometimes called “sulfate of potash” or SOP.2,3 

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