Potassium deficiency in cotton across the Southeast is a major problem for producers, even more so this year, says Glen Harris, University of Georgia soil fertility and Extension specialist.
“It’s been a continuing problem. In my opinion, I think we do a decent job with nitrogen. We don’t seem to have a lot of phosphorus problems. Potassium is probably our No. 1 nutrient issue every year,” Harris said. “It kind of comes and goes but this seemed to be one of those years where we saw a lot of it.”
Why Does it Happen?
Theories vary on why the nutrient came up short this year in cotton plants. Some believe the rainfall in the late summer and fall contributed to its deficiency, especially since it is mobile in the soil. However, Harris said it is not as mobile as nitrogen and we have experienced decent rainfall in prior years and did not have unusual potassium.
“I really wonder if there’s other things going on. I think part of it is, we’re seeing higher calcium levels and I think that’s starting to interfere with potassium uptake,” Harris said. “People for some reason are running their pH’s higher which also usually comes with higher calcium levels. Calcium competes with magnesium to get into the plants. That’s a theory, but I’m wondering if that had something to do with it.”
Potassium is one of the primary nutrients plants need to grow.
“Carbon, hydrogen and oxygen are the top three, but we don’t talk a lot about those because we get them free from air and water. The next three are N (nitrogen), P (phosphorous), K (potassium) and I rank them N-first, K-second, probably for Georgia cotton as far as need,” Harris said.
Potassium deficiency itself is detrimental to the plant. But it could also lead to secondary problems like the fungal disease leaf spot.
“If you read the textbook, it’ll say the older leaves will turn yellow and eventually turn yellow around the outside like dead tissue around the edge of the leaf. My experience has been, it’ll occur almost on the leaves of the whole plant. We also get leaf spots that will come in, too,” Harris said. “We’ve seen enough of it over the years, people are pretty good at diagnosing it, which is also kind of scary because we think we know what to do to avoid the problem and we know what it looks like when it shows up, but we keep getting it. That is concerning.”
How to Avoid Potassium Deficiency
There are various ways to combat this nutrient deficiency. Do not wait too late to apply potash. Soil test and grid sample, since most of the time, these instances will occur in patches in the field. Also, do not split your fertilizer applications. Apply all at planting.