Many, many questions have been received over last week about how to manage the supply of nitrogen in light of more acres of early planted corn, and the need to plant cotton. While all forms nitrogen may not be readily available we need to keep perspective on our options. This will sound strange coming from the ‘Cotton Guy’, but right now we need to make sure that our corn crop has adequate nitrogen fertility. Nitrogen availability is much more critical in corn than cotton so take care of your corn first. While I would rather see you plant cotton, I realize with all the corn acres in Tennessee this year we need to do everything possible to produce to high yielding crop. Nitrogen is ‘in the pipeline’ for delivery and we have until squaring to apply nitrogen on our cotton. If you planted cotton today (4/25), you have 45 days (June 5th) to apply N fertilizer for maximum effectiveness. There is plenty of time for N delivery.
Options for N application in cotton are many:
1.) Apply full amount as dry or liquid N pre-plant.
2.) Apply a percentage of dry or liquid N pre-plant and the balance side dress.
3.) Apply Liquid N as your carrier for burndown or pre-emergence herbicide applications.
4.) Apply dry N with a spreader after emergence.
5.) Apply liquid N with a coultered rig or possibly hoods after emergence.
DO NOT apply liquid N over top of emerged cotton at any growth stage. Severe damage and crop loss will occur. DO NOT rely solely on foliar N products to supply the N required for cotton. You will be growing the crop off of residual nitrogen in the soil which is not uniform and varies based on cropping history. If you make a surface application of 32% UAN or urea, DO ADD a nitrogen stabilizing product to prevent loss. Cotton requires approximately 50 units of N per bale of lint produced. On dry-land acres in Tennessee 80 units of N will provide the best economic return on your N investment. Remember that cotton responds to excess N with rank growth, boll rot, and can slow harvest. So how do I expect you to produce a two bale crop or more on 80 units of N? Remember the soil contains residual N and will supply the crop if conditions are such that more N is needed. In 16 trials conducted on-farm from 2008-2010 cotton yielded 800 lb or more of lint even with 0 N applied. When we apply N to cotton we meet the nutrient requirement as well as reduce variability in yield by making available N more uniform across the field. I did not say ‘Don’t apply nitrogen to cotton and yield 800 lb!’. This discussion is just to illustrate that N use by cotton is less critical than in our corn crop. Please contact your County Extension Agent or myself directly is you have questions.