With cotton planting dates varying widely across the state, time for sidedress fertilizer may or may not be fast-approaching. Regardless of planting date, demand for nitrogen (N) increases significantly after first square, so sidedress N applications should be made between first square and first bloom to ensure the plant has adequate N when it is needed most
For cotton, our base recommendation for nitrogen is 90 lbs N per acre—split one-third at plant and two thirds at sidedress—regardless of soil type. However, this recommendation should only be used as a guide. There are a couple of scenarios in which we may want to back off the 90 lbs N per acre recommendation.
For example, if excessive vegetative growth has caused problems with late-season insects or boll rot, N rates should be reduced by 20-30 lbs N per acre. For late-planted cotton, reducing N may also help prevent issues with late maturity. On the other hand, if vegetative growth has been inadequate in the past and planting was timely, N rates may need to be increased slightly.
Remember that 10 to 15 pounds of sulfur (S) per acre is recommended for optimum cotton yields. Sulfur can be applied with at-plant and/or sidedress fertilizer applications. Many N sources already contain S. It is recommended that S be applied in the sulfate form—not as elemental sulfur—since it can take several months for elemental sulfur to be converted into plant-available forms.
For urea-based fertilizers, significant volatilization losses can occur if fertilizers are not applied before a rain or irrigation event. If 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.