Much of our early planted corn has exhibited signs of potassium deficiency after going through the May to early June dry spell. This article is a basic reminder of how potassium works in the plant so you can make informed decisions on whether you need to apply more potassium.
Potassium uptake occurs by diffusion where nutrients move to the root surface along a concentration gradient from high to low concentration. The effect of dry weather on root growth results in potassium deficiency symptoms. Other conditions such as compaction, herbicide root injury, or insect damage can compound root development issues and potassium uptake.
Identifying K Deficiency
Potassium is mobile in the plant which is why the lower leaves show deficiency first. The plant moves available nutrients to prioritize new growth. Potassium deficiency symptoms include yellowing to necrosis of the leaf on the outer edges or leaf margins, as opposed to nitrogen which starts from the leaf tip to the midrib.
If the symptoms were a result of dry weather and not a soil deficiency, the new growth should appear normal as soil moisture is replenished and root growth improves. Corn begins to rapidly uptake potassium after V6 as demand increases (Figure 1). While the symptoms on the lower leaves will remain, no yield loss is expected due to a deficiency at the early stages (Swayer, 2000).
If you have a recent soil test that did not show a deficiency, then any visible symptoms are likely a result of dry weather or slow root growth. However, if your soil samples were pulled during extremely dry weather like we had last fall and this spring, it could impact your results. We covered this in episode 109 of the Agronomy and Farm Management Podcast. Listen in for more details. You can also learn more about how soil test potassium levels and pH are affected by low soil moisture by clicking here.
In summary, if your corn has outgrown the deficiency symptoms, then no action is needed and you should not expect an impact on yield. If the new growth continues to show symptoms, then you can confirm the visual symptoms with a tissue test and follow up with a soil test under adequate conditions.
Bender, Ross R. et al. “Modern corn hybrids' nutrient uptake patterns.” Better crops with plant food 97 (2013): 7-10.
Sawyer, J. (2000.). Corn leaf potassium deficiency symptoms. Potassium deficiency symptoms in Corn | Integrated Crop Management. https://crops.extension.iastate.edu/encyclopedia/potassium-deficiency-symptoms-corn