Potassium (K) is an essential nutrient in corn production. It is associated with movement of water, nutrients and carbohydrates in plant tissue, and if deficient, growth is stunted and yields are reduced.
It has been shown that K stimulates early growth, increases protein production, improves the efficiency of water use, and improves resistance to diseases and insects. However, unless one is tuned to detecting symptoms of K deficiency, one can lose yield year to year in both field and sweet corn production.
The total K content of soils frequently exceeds 20,000 ppm (parts per million). Nearly all of this is in the structural component of soil minerals and is not available for plant growth.
Three forms of K exist in soils — unavailable, slowly available or fixed, readily available or exchangeable. Usually the unavailable and slowly available forms are not considered essential to plant growth. The readily available portion is the one usually extracted in soil testing and gives a grower a sense of how much K is needed for corn production.
Usually, less than 150 ppm K in your soil test indicates you have low levels and anything above 250-800 ppm is high to excessive. Depending on wet or dry weather and type of soil, your corn plants can exhibit deficiencies even when your soil tests indicate medium levels of availability.
When is it too late to tell if potassium nutrition was a problem? K deficiency symptoms, when they exist, are usually best observed early in the season. During vegetative growth stages, K-deficient corn may show yellow or brown leaf margins. Such symptoms, however, may be difficult to detect at harvest. As the end of the season approaches, it's a good idea to learn what signs and symptoms your plants show to start planning for next year.
At the end of the season, corn still can provide some visual clues about K nutrition. Ears may be low to the ground, stalks may be broken or lodged, and ears may be smaller and lighter, with unfilled tips. The following is a list of things to look for at the end of the season for K deficiency:
- Insertion of ears at lower nodes.
- Shorter ear length and narrower ear diameter.
- Reduced grain weight.
- Incomplete grain filling.
- Premature black layer formation in seeds.
- Accelerated leaf senescence.
- Shortened internode length.
- Narrowed stalk diameter.
- Thinner stalk rinds.
- Weaker stalks.
- Increased incidence of stalk breakage and lodging.
- Increased susceptibility to stalk rot.
If you see any of these signs, it may be time to reevaluate your potassium fertility program. This assessment is best made by taking a soil test and conferring with a knowledgeable consultant, adviser or agent. You may plan to take a few plant tissue samples from this season or the next crop to monitor potassium nutritional status during the season.