Cotton Response to the Rate and Source of Sulfur on a Sandy Coastal Plain Soil

Abstract

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 was conducted in south Alabama on a Lucy loamy sand (loamy, kaolinitic, thermic Arenic Kandiudults) to evaluate the response of cotton (Gossypium hirsutum L.) to the source, rate, and timing of S fertilizer applications. Sulfur was broadcast preplant as either ammonium sulfate, elemental S, potassium sulfate, potassium thiosulfate, or K-Mg-sulfate at rates of 0, 10, 20 and 40 lb S/acre. Additionally, ammonium sulfate was applied at first square to evaluate timing effects. Lint yields were increased each year and they peaked at a rate of approximately 20 lb S/acre on this Lucy Is soil. Averaged across sources, 20 lb S/acre increased lint yields by an average of 21% as compared with the no S check treatment. Lint yields were not affected by time of S application in 1993 or 1995, but a preplant application of S increased yield compared with S applied at first square in 1994. The response to time of S application was attributed to heavy rainfall that was received soon after 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 extremely wet growing season. Lint quality, as measured by high volume instrumentation (HVI), was not affected by any S treatment in 1993 or 1994. In 1995, fiber length increased with S rate, but the differences among sources were inconsistent. Results of this test suggest that cotton produced on sandy Coastal Plain soils that are low in S may require annual applications of 20 lb S/acre to ensure high yields. The S should be applied preplant, although delaying application to first square should not limit yields. For lint production, differences among commercial S fertilizer sources should be minimal.