Carolina Cotton Notes - July 14, 2006

I am getting some questions on foliar applications of nitrogen to cotton that seems to just be "sitting there". We have even seen some square shed not associated with plant bugs. Y'all probably know I am not usually the first one to recommend foliar applications. In this case I think we have some restricted root development due to excess water (lack of O2). In addition, we may have lost some nitrogen due to leaching and/or denitrification. Because of these factors I would not try to talk someone out of applying foliar Nitrogen to help the cotton along until, hopefully, the roots start to find Nitrogen. This will be a year when petiole tests may be more valuable than in many other years. I would rather do a good job of testing a few fields (that are representative of other fields in terms of soil type and rainfall) on a weekly basis than to go out and test all the fields only one time.

Nitrogen can be supplied foliarly by diluting dry or liquid urea. Potassium nitrate can be used if K is also needed. Potassium nitrate is usually applied in a mixture of a pound of potassium nitrate per gallon of water. Using ground equipment you can apply up to 20 gallons per acre. Five gallons per acre is usually applied by air.

There are some fancy foliar fertilizers that claim to have "better forms of nitrogen". If you need N, urea will supply it fine, if it is available. Feed grade urea is less likely to cause leaf burn because it has low biuret levels. The following tables lists urea rates for normal cotton and well watered cotton based on the application volume you are able to deliver

Table 1. Options for foliar application of urea to dryland cotton (leaves do not wilt by noon)


#N/acre	# 46% urea	gal. of 23% N Urea	application volume
4.6	10	2.1	5 gallons
5.5	12	2.5	10 gallons
6.9	15	3.1	15 gallons
9.2	20	4.2	20 gallons

Table 2. Options for foliar application of urea to irrigated cotton or fields that have had recent rainfall*


#N/acre	#46% urea	gal. of 23% N urea	application volume
6.6	14	3.0	5 gallons
7.8	17	3.5	10 gallons
9.2	20	4.2	15 gallons
11.5	25	5.25	20 gallons

* Caution: These rates can cause leaf burn if leaves contain inadequate moisture, especially when two or more consecutive weekly applications are made.