Cotton fields throughout Alabama are approaching time for nitrogen (N) sidedress applications. Nitrogen is the nutrient that is most likely to cotton yields if it comes up short, and it is important to apply N out at the right time and at the right rate to maximize yields.
Here are three common questions about sidedressing:
#1. How much N should I apply at sidedress?
Most research throughout the Southeast shows that a rate of 90 lbs of N per acre maximizes yield and return on N investment. If 20 to 30 lbs N per acre was applied at plant, this means 60 to 70 lbs N per acre should be applied at sidedress.
Remember, it is possible to apply too much N. Not only does excess N reduce producers’ return on investment, it can also result in lint yield reductions. Nitrogen rates exceeding 120 lbs N per acre may cause excessive vegetative growth, delayed maturity, and increased susceptibility to insect damage.
Arguably, some of the foliar diseases observed in recent years are worsened by aggressive N rates.
#2. Should I increase my N rate if heavy rains have occurred in my fields?
In fields that experienced excessive rainfall following “at plant” N applications, consider adding an additional 10 lbs N per acre on sandy soil types. Repeated heavy rains in sandy soils can lead to some leaching losses of N.
#3. When and how should I apply N?
Sidedress N should be applied between 1st square and 1stt bloom to maximize uptake of N when the plant needs it most. Most N is applied by broadcast application of granular products or dribbling of liquid products between the rows.
If UAN (liquid N in the form of urea ammonium nitrate) is applied, it is important to minimize the amount of UAN which contacts the leaves and stems, since UAN can burn plant tissues. For urea-based fertilizers, significant volatilization losses can occur if fertilizers are not applied before a rain or irrigation event.
If a rain is not predicted within 2 to 3 days after urea application, addition of a urease inhibitor with the active ingredient NBPT can reduce potential N loss.