Gandy fertilizer spreader in Cotton field

A multi-year cotton fertilization research trial is being conducted in the Panhandle, with 6 nitrogen rates: zero, 45, 90, 135, 180, and 225 units of N for the growing season. Credit: Madelyn Grant, UF/IFAS


Madelyn Grant, Escambia County Extension, Ethan Carter, Regional Row Crop IPM Agent, and Hardeep Singh, UF Cropping Systems Specialist


Cotton rows close up

Preliminary data from 2022 trials in Jay and Marianna indicated that the current UF/IFAS recommendation of 60#N/acre did not provide optimal yields from modern commercial cotton varieties. Credit: Madelyn Grant, UF/IFAS

University of Florida researchers are now a year and a half into the nitrogen rate study to evaluate Florida’s nitrogen recommendations for optimal cotton production. The current UF/IFAS cotton recommendation calls for 60 units of nitrogen/acre, which has been argued by growers as insufficient for optimal yields with current varieties and varying soil types. This issue was exacerbated by Florida Senate bill 712, which mandates cotton growers follow the UF/IFAS recommended rates in BMAP areas, with an exception for leaching rain events.

This multi-year research project is being conducted at multiple locations across the Florida Panhandle. The trial compares six nitrogen (N) rates at multiple locations: zero, 45, 90, 135, 180, and 225 units of N through the growing season. Some rates were higher than what commercial farmers would use to help determine the plateau of the optimal N rate for Florida cotton production.

igure 1 Mid-Season 2022 plots areal photo

Figure 1. Visual representation of the 2022 plots at WFREC Jay (all rates duplicated in Marianna) during the growing season.

Figure 2 2022 plots areal photo pre-harvest

Figure 2. Visual representation of the 2022 plots at WFREC Jay (all rates duplicated in Marianna) after defoliation and prior to harvest.

Year One Results and Summary

Yields from year one established baseline data and the necessary foundation to begin the adjustment of the recommended UF/IFAS nitrogen rate in cotton. The current UF/IFAS Soil Lab recommendation of 60 lbs./N was not adequate for optimal yields in the first year of comparison of commercial varieties. This was corroborated by the preliminary yield tables from our two 2022 research station sites at Jay and Marianna. Each location found that nitrogen at a minimum of 90 lbs./A was statistically significant for best yields in 2022. Granted, this was just one year of data from test plots on UF/IFAS research stations.

Figure 3. Graphical yield representation from WFREC Jay using seed cotton weight.

Figure 4 Marianna Cotton Yield Chart

Figure 4. Graphical yield representation from NFREC Marianna using seed cotton weight.

Year Two Status and Update

For 2023, the Marianna site was relocated to two separate commercial farms with sandier soil than that of the research station to determine if similar results are repeated. The Jay site remains unchanged. Long term, we expect the UF/IFAS rate to become a range, based on farm practices (tillage type, cover cropping, livestock integration) and soil type. Other cotton nitrogen rate research is also being performed simultaneously by evaluating nitrogen calibration strips in fields.  This complete body of work will be integral for updating recommended nitrogen rate(s) for cotton in Florida.

Madelyn Grant
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