Sidedressing Georgia Cotton with Nitrogen and Potassium in 2024

In all my 30 years working for UGA in Tifton this is the wettest month of May I can remember. It is not uncommon for the low end of my garden at my house to flood in March…but it rarely happens in May. May is supposed to be one of our drier months which usually works out well for getting the crop planted. I am amazed that the rains in May did not delay cotton planting more than they did. We may have a little more June-planted cotton than normal, but it doesn’t seem to be that far off.

Of course with multiple, heavy rains in May there are questions about nitrogen (N) management such as “I put some preplant N out, did I lose it all?” and then the other extreme, “I didn’t get a chance to put preplant N out and now its sidedress time – how much does that hurt me?”. It is good to remember that the standard UGA recommendation is to put ¼ to 1/3 of your total N out at planting and then the remainder at sidedress between first square and first bloom. So, if you applied say 30 or 40 lb N/a at planting in early May and got a lot of rain, you can simply bump up your sidedress N rate by 20 lb N/a or so to recover. If you were unable to get any preplant N out and now its sideedress time you can simply put the full rate of N you were planning to use all at sidedress. Research studies in the past have clearly shown that if you can only apply nitrogen one time on cotton, at planting or at sidedress, at sidedress is the preferred situation.

For June planted cotton, especially mid-June planted, it is important to remember not to try to catch up with high N rate early. It seems backwards because you want to try to “speed up” the crop. But this can actually backfire since if you get too much vegetative growth early and the plant doesn’t shift to reproductive growth on time you will lose yield potential. In other words, there is not as much time to fruit and put on bolls when planting in late June and you don’t want to delay fruiting. Also, don’t forget that if you come up a little short on N later in the year for a May or June planted, you can also do some foliar feeding, especially anytime between the 3rd and 6th week of bloom.

And then there is potassium (K). With all the rain in May this year there has been a lot of concern with leaching of potassium and questions about replacing it too (along with N). The thing to remember is that K is not as mobile or as “leachable” as N in soil. Phosphorous (P) is very immobile so yes, compared to P it is mobile. But compared to N, K is not as mobile. What does this mean in practical terms? I do believe the “big rains” in May likely moved K down deeper into the soil profile. But I believe the cotton roots will eventually get down to those levels and recover it. On the other hand, the wet, saturated soil may have also comprised the cotton root system, that is the roots may not be as deep and robust due to the wet conditions. In this case there may be some benefit from adding some sidedress K when you sidedress N. Unfortunately this is easier to do with granular materials like KMag and muriate of potash than “liquid K” (it’s hard to get a decent shot of K per acre when adding liquid K to liquid N sidedress.

Normally, I would encourage Georgia cotton growers to apply all their recommended K at planting instead of split applications. It also depends on how you split the K rate. For example, if you put all your recommended K out at planting and then put some “extra” in at sidedress that certainly is not going to hurt anything. And in a year like this year, which is not normal (getting a lot of rain in May. And is there even such thing as a “normal” year anymore?) spreading some KMag or muriate of potash at sidedress with your N may not be a bad idea at all. And finally, if we get into the peak bloom period and start seeing a lot of K deficiency and leafspot (and I suspect we will) we can also do some foliar feeding of K. And if you need both N and K they can be foliar fed together. My hope is that this year’s cotton crop progresses with a good yield potential and needs some foliar N and K to make some good yields !

Dr. Glen Harris

Extension Agronomist
UGA Crop & Soil Science

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