Potassium Deficiency in Forage Corn

Potassium is a macro nutrient, required by all plants in considerable amounts, along with the other two macro nutrients, nitrogen and phosphorus. While we know that, in general, potassium is important to photosynthesis, strong stems, disease resistance and fruit quality, in silage or field corn, potassium is required to produce tall plants with large leaves, prompt tasseling and silking, and to minimize lodging. How do we recognize whether our corn is deficient in potassium?

There are several symptoms to indicate a potassium deficiency. The best known symptom is a “scorched” appearance of the outer edges of leaves, especially the oldest leaves. Meanwhile, the midrib, or leaf center, remains green. This is a typical symptom in grassy plants.

As mentioned above, sufficient potassium results in nice, large leaves. When potassium is deficient, leaves can be considerably smaller. Hard to visualize, unless you are making a side-by-side comparison with non-potassium deficient plants.

Slow development is a noticeable symptom of potassium deficiency in silage corn. It can result in delayed tasseling and silking. Most farmers choose varieties with the highest possible heat units; as the longer the heat units, generally the greater the yield. These varieties push the boundaries, maturing just in time at the end of the year. That means the highest quality levels and the highest yield. If development is delayed, due to potassium deficiency or other reasons, you won’t obtain the maximum tonnage or quality from your corn.

Another symptom of potassium deficiency is early and increased lodging. Work done by the International Plant Nutrition Institute (IPNI) has shown that low potassium is a cause of increased lodging for a couple of reasons. Stalk weakness and breakage is related to a high N:K concentration in the stalk. This can commonly occur if producers over-fertilize with nitrogen without paying enough attention to soil tests that might show low potassium. The result is a breakdown of the pith of the brace roots. This weakens the plant, and over it goes in breezy conditions. Also, low potassium has been shown to increase the severity of fungal disease which can also cause lodging.

Scorching of the leaf margins is usually the best-known and the first indication of potassium deficiency in silage corn. You can’t easily increase potassium after the symptoms have begun to appear. The best remedy is to plan well, get a soil test done early, and make sure enough potash fertilizer is applied prior to planting.

References: Visual Indicators of Potassium Deficiency in Corn. Murrell, T. S. Better Crops, Vol. 94 (2010, No. 1). Soil Fertility Manual. IPNI, 2006.