Some crops exhibit characteristic deficiency symptoms when adequate amounts of K are not available for growth and development, according to University of Minnesota Extension soil scientists. Potassium is mobile in plants and will move from lower to upper leaves. For corn, the margins of the lower leaves turn brown. This development of dead tissue is accompanied by a striped appearance in the remainder of the leaf. The entire leaf has a very distinct light green appearance when viewed from a distance. The striping associated with K deficiency in corn can be easily confused with deficiency symptoms for sulfur (S), magnesium (Mg), and zinc (Zn).
The margins of the leaflets turn light green to yellow when K is deficient for soybean production. As with corn, these deficiency symptoms first appear on the lower leaves. With maturity, the deficiency symptoms expand to leaves closer to the top of the canopy. It is not uncommon to find K deficiency symptoms near the top of the plant in isolated field areas with intense soybean aphid pressure. In this case the deficiency is not necessarily related to a deficiency of K in the soil.
Potassium deficiency in alfalfa is characterized by yellow or white spots on the margins of the leaflets, with symptoms first appearing on the older plant tissue. Potassium deficiency in alfalfa can be easily confused with damage caused by the potato leafhopper.
Potassium deficiency in potato occurs as scorching of the leaflet margins on the older leaves first. Symptoms are usually first noticeable during tuber bulking (mid-July) as the tuber is a strong sink for potassium. Potato vines deficient in potassium will dieback prematurely, which can often be confused with diseases causing vine death.