COTTON RESPONSE TO THE RATE AND SOURCE OF SULFUR ON A SANDY COASTAL-PLAIN SOIL

Cotton acreage in the Coastal Plain of the Southeast has increased in recent years. The soils in this region are sandy and typically have a low retention capacity for sulfate S. A 3-yr (1993-1995) field test wa s conducted in south Alabama on a Lucy loamy sand (loamy, kaolinitic, thermic Arenic Kandiudults) to evaluate the response of cotton (Gossyp ium hirsutum L.) to the source, rate, and timing of S fertilizer appli cations. Sulfur was broadcast preplant as either ammonium sulfate, ele mental S, potassium sulfate, potassium thiosulfate, or K-Mg-sulfate at rates of 0, 10, 20 and 40 Ib S/acre. Additionally, ammonium sulfate w as applied at first square to evaluate timing effects. Lint yields wer e increased each year and they peaked at a rate of approximately 20 Ib S/acre on this Lucy Is soil. Averaged across sources, 20 Ib S/acre in creased lint yields by an average of 21% as compared with the no S che ck treatment. Lint yields were not affected by time of S application i n 1993 or 1995, but a preplant application of S increased yield compar ed with S applied at first square in 1994. The response to time of S a pplication was attributed to heavy rainfall that was received soon aft er the first square application of S. Sources of S did not affect lint yield in 1993 or 1995, but ammonium sulfate and K-Mg-sulfate produced slightly higher yields than those of other sources in 1994, an extrem ely wet growing season. Lint quality, as measured by high volume instr umentation (HVI), was not affected by any S treatment in 1993 or 1994. In 1995, fiber length increased with S rate, but the differences amon g sources were inconsistent, Results of this test suggest that cotton produced on sandy Coastal Plain soils that are low in S may require an nual applications of 20 Ib S/acre to ensure high yields. The S should be applied preplant, although delaying application to first square sho uld not limit yields. For lint production, differences among commercia l S fertilizer sources should be minimal.