Reports of signs of potassium deficiency in both corn and soybeans are coming across Jim Camberato’s desk. He is an Extension soil fertility specialist at Purdue University. Most people assume that the symptoms have shown up because of soil compaction and the drought conditions across most of the state.
Camberato acknowledges that both soil compaction and drought can stress plants and make symptoms of a nutrient deficiency like potassium more likely to appear. However, he stresses that there is also a chance that the shortage in the soil is real, not just an artificial situation created by the inability of roots to access the nutrient. Camberato believes that there are fields or parts of fields that actually need potassium applications to bring them into the range that will prevent nutrient deficiency symptoms from occurring.
In this case, the symptom is browning around lead edges in corn. The symptoms progress inward from the tip as the deficiency becomes more severe. If there is a potassium deficiency in soybeans, there is also browning of the edges of soybean leaves, especially in the early stages when the deficiency first appears and is noticeable in the field.
Camberato’s point is that if you find these symptoms in a field, you shouldn’t write it off to the drought and poor growing season. Instead, you should pull soil tests and determine if potassium levels are in the correct range or not. He has seen situations where people didn’t think the K shortage was real, but it turned out that the amount of potassium in the soil was low, well below acceptable levels for corn or soybeans.
Even in fields where broadcast fertilizer was applied, sometimes the spreader doesn’t get fertilizer to the edges of the field or there are skips an misses in application. The only way to know that the problem is artificial caused by conditions and not caused by an actual deficiency in soil potassium levels is to pull soil tests, he concludes.