At the end of important football games the players on the winning team often take a bushel basket full of ice and an orange electrolyte-laden beverage and douse their coach’s head with it. This particular beverage is routinely consumed in large quantities by sweating athletes. Electrolyte packages are designed to replace minerals lost through perspiration. If deficient in electrolytes (including salt), hard-working athletes are prone to getting cramps. The main electrolyte compound in most sports drinks is monopotassium phosphate. Somewhere in our human digestive and circulatory systems, the potassium (K) dissociates from the phosphate and joins up with the other positively charged minerals (called cations): calcium (Ca), magnesium (Mg), and sodium (Na). On your soil tests, base saturation percentage (BSP) values are stated for each of these cations: K, Ca, Mg, and Na. Not all labs routinely perform these BSP tests; I only work with labs that do.
In hot weather, cattle and horses drink a lot of water, and consume much salt (for them Na is a more critical nutrient than potassium). Also in hot weather, growing crops metabolize a lot of water, but rather than salt (NaCl), the electrolyte they need the most is potassium. According to my Eco-Farm — Acres USA Primer (Walters and Fenzau, 1996), “Potassium is a prime requirement in the chlorophyll building chore. Plants need it before they can pull free nutrients out of the air: carbon, hydrogen, oxygen. In fact, plants can’t make starches, sugars, proteins, vitamins, enzymes or cellulose without potassium. They can’t even survive summer dry stretches very well without ample potassium.”
In the unusually warm weather that we’ve been experiencing in the Northeast, moisture management in plants has been a critical concern. Potassium is the element most responsible for regulating how the stomates open and close. Stomates are microscopic holes on leaf surfaces where moisture and oxygen escape. When moisture is too limiting (such as in droughty conditions), the stomates constrict — a self-preservation mechanism. This is why corn leaves curl, and get spikey (my term). When precipitation finally arrives (assuming its absence hasn’t been for too long a period), the corn leaves unfurl, and growth resumes. Understand, though, that the maturing process continued during the droughty period. Potassium deficiency increases the odds of plants not recovering optimally, once the heavenly spigots are turned back on. Another prominent K deficiency symptom is reduced standability, commonly referred to as lodging. Other deficiency symptoms — according to the Primer — are most visible in grasses (such as corn). And they include mottling, brown top, purplish spotting, and streaking or curling of leaves. In grains and grasses, firing starts at the tip of the leaves, and proceeds down from the edges, usually leaving the midrib green. This K deficiency symptom is basically the opposite of the primary symptom of a nitrogen deficiency: the classic N deficiency resembles an arrowhead which starts at the leaf tip and follows the midrib, almost as if attempting to split the leaf symmetrically. In almost all cultivated plant species a potassium deficiency can result in premature leaf loss and reduced resistance to cold.
Potassium deficiency affects crops and athletes, and it impacts another category somewhere between those two groups, namely livestock. In hot weather, many livestock nutritionists recommend increasing potassium intake to ruminants (as well as horses and hogs). Whether in the form of sweat, or fluid moved through the kidneys, the extra water consumed due to the heat results in the loss of all four of the cations mentioned above. Unlike soil phosphorus — which is often very limited — most soils have plenty of K. Not only that, the K supply in the oceans… though much less than the Na supply… is considered to be inexhaustible.
The actual availability of potassium to the plant is a separate matter. Quoting again from Walters’ Primer: “Unless microbes in the soil give a mighty assist, and pH is managed at the proper acid level, potassium availability is a massive problem. It is not helped by the kind of fertilizers available either. When corn is starved for want of available potassium, is gets plugged up with iron at the nodes. As a consequence, sugars and starches can’t travel from leaves to roots. Roots starve. Root and stalk rot becomes the observed result.” Walters stresses that K has a character of its own, much like Na, except that it is found in many rock formations, usually in small amounts. Let me point out that larger soil particles — like sands and “big” silts — tend to offer scarcer K resources, largely due their lower surface-to-mass ratios. Thus a gravelly silt loam proves to be a chincy source of K, compared to clayey soils. The normally desirable permeable soil — with its lower K reserve — proves to be a two-edged sword targeting the crop person. According to Walters, the preferred BSP for K is 3 percent.
Levin, a Central New York dairy farmer, called me out to examine a three-acre mixed-mostly grass hay stand which was evidencing extensive leaf-blade side die-back. Upon examining the field, I theorized that it might be suffering from a K deficiency. Recently, I sampled the soil in question, sending the sample to the Dairy One Lab in Ithaca. The results came back in just a few days: pH 6.7; Ca and Mg were very high; phosphorus was high medium, and K was low medium. The BSP for K was a paltry 1.0. The recommendation was for 86 pounds of potash per acre; so I’m suggesting a 0-0-51 sulfate of potash. Levin said to treat half of the field — leaving the other as a control. We’ll do that ASAP.
Thinking about electrolytes and hot weather makes me recall a story my mother told. She said that as a young teenager — back on their Iowa farm — she told her prim and proper spinster aunt, who was an English teacher, that she was sweating a lot due to the hot weather. Her aunt replied: “Marjorie, horses sweat, men perspire, but women glisten.”