Field studies were conducted during 1995-1997 to evaluate cotton (Gossypium hirsutum) response to the source, and timing of N fertilizer applications. The test was conducted on an irrigated Lucy loamy sand (Arenic Kandiudults). Treatments included N sources, timing of N application (ammonium nitrate) and split applications of N (ammonium nitrate & ammonium sulfate). Nitrogen sources applied preplant included: 1) ammonium nitrate (34-0-0), 2) ammonium sulfate (21-0-0-24.2), 3) urea (46-0-0), 4) urea-ammonium nitrate solution (UAN; 32-0-0), 5) UAN + ammonium thiosulfate (28-0-0-5). The non-sulfur containing sources were applied with and without S. For these treatments, S at a rate of 40 lb/acre was applied preplant as gypsum. Times of application for ammonium nitrate were preplant, first true leaf, first square and first bloom. Split applications of ammonium nitrate and ammonium sulfate were made by applying half of the N preplant and the remaining N at first square. Two additional treatments received split applications (preplant/first square) of N as a 50:50 mixture of ammonium sulfate with urea or ammonium nitrate. To evaluate the effects of supplemental applications of K on cotton yield, ammonium sulfate was applied in combination with 60 lb K₂O/acre. These treatments were applied as a two-way (preplant/first square) or three-way (preplant/first square/first bloom) split. All N sources were applied at a rate to supply 90 lb N/acre. Statistical analysis of the data showed some minor differences among sources, but overall the results of this three-year study show that there were no superior N sources since the sources tested produced similar lint yields. For ammonium nitrate, preplant applications of N were sufficient in two out of three years. Likewise, split applications (half preplant and half at first square) of ammonium nitrate did not improve yields as compared to applying all of N preplant. Data from the non-sulfur containing sources that received supplemental S as gypsum suggests that both the N and S fertility requirements need to be considered when producing cotton on coastal plain soils. Applying ammonium sulfate with supplemental K did not improve yields as compared to ammonium sulfate or ammonium nitrate. Likewise, a 50:50 mixture of ammonium sulfate and ammonium nitrate or urea split applied (half at planting and half at first square) did not improve yields as compared to ammonium sulfate or ammonium nitrate applied alone. Lint quality was not affected consistently by any of the N fertility treatments.