Managing Nitrogen With Scattered Rainfall Conditions
DR. ANGELA MCCLURE
JACKSON, TENN.
With recent weather events in the Midwest, corn prices have started to climb and growers are paying closer attention to protecting corn yield. In the past month, rainfall in Tennessee has been much more scattered to practically nonexistent and we aren’t used to these dry spells compared to past years. Most of the calls I have had this week, dealt with concerns about nitrogen applications that went out prior to a 2 to 3 (or more) week dry spell. Surface N applications that go without an incorporating rain cannot benefit the crop. Rainfall helps move soil applied N through the profile and stimulates crop root growth for uptake. Fortunately, with warm weather and adequate subsurface moisture, nitrogen is mineralized from organic matter and smaller corn has a low N requirement. But, requirements are increasing greatly as we move into June.
For surface N that has gone out:
• Irrigate N in by applying at least 0.25″ water. For granular urea or UAN with no NBPT (Agrotain) stabilizer, apply irrigation within 2 days of fertilizer application.
• In dryland fields, document application date and date of first incorporating (0.25 or more) rainfall event. If more than 3 weeks have passed, consider topdressing an additional 30 to 40 units of N in fields with expected good yield potential. For fields in ‘dry zones’ that continually miss rain, we may need to reduce our yield goal and manage for lower yield.
If sidedressing N in dry conditions:
• Granular material can more easily slide through surface residue versus UAN. Apply NBPT stabilizer to granular urea. This will buy a few weeks protection from surface volatilization loss and ‘wait’ on an incorporating rain. Check labeled rates of some generic products and make sure to apply the higher end rate.
Do not broadcast UAN. It will adhere more to surface residue than granular material, increasing likelihood of surface volatilization loss without timely rain. Instead, inject or spray down into the soil behind a coulter or dribble/spray in a narrow band to minimize surface area exposed to volatilization loss. Add NBPT stabilizer to surface applied UAN if rain is not expected within a few days.
• Check out Larry Steckel’s latest on weed control! Weeds rob soil moisture and nitrogen from the corn crop. ∆
DR. ANGELA MCCLURE: Extension Corn and Soybean Specialist, University of Tennessee