Agronomic Services — News Release
FOR IMMEDIATE RELEASE
MONDAY, MAY 22, 2000
Cotton needs sulfur on Coastal Plain soils
RALEIGH — Many farmers in the Coastal Plain will need to fertilize their cotton with sulfur this year. Sulfur leaches rather easily on sandy textured soils, especially where the clay layer is 12 to 15 inches below the surface. The excessive rainfall from hurricanes Dennis and Floyd probably washed sulfur out of the root zone. Even without the rain, very little residual sulfur is carried over from one year to the next. Therefore, sulfur application is often a yearly requirement on sandy Coastal Plain soils.
Coastal Plain soils tend to be low in sulfur for several reasons. Many are low in organic matter, which is a major source of sulfur, and most are sandy and tend to loose nutrients easily, especially during rain events. Several factors increase the problem: high analysis fertilizers that contain little or no sulfur, high-yielding crops that remove sulfur from the soil, reduction in crop residue turned to the soil, stringent restrictions on industry sulfur emissions, and a decline in the use of sulfur-containing pesticides.
Sulfur-deficient plants are stunted and exhibit a uniform yellow coloration. These symptoms occur in the young leaves near the top of the plant. Similar symptoms occurring on the bottom leaves probably indicate a nitrogen deficiency. Sulfur deficiencies cause slight to severe yellowing, depending on the amount of sulfur in the soil. In severe cases, the entire plant will turn yellow.
Sulfur is an essential component in the synthesis of plant proteins, enzymes, and chlorophyll. Without sufficient sulfur, plants cannot achieve optimum growth and yield. Reduced stalk growth and boll development are likely to occur. When soils are deficient, an application of sulfur can increase cotton yields by 20 percent.
Cotton needs from 15 to 25 pounds of sulfur per acre for optimum lint production under most circumstances. On soils with a deep sandy surface where problems with sulfur have been observed in the past, it's good insurance to apply sulfur with any pre-plant fertilizer application. If sulfur is not applied before cotton is planted, it should be included with the nitrogen side dressing.
Some fertilizer products that contain sulfur include elemental sulfur, 30-90% S; ammonium sulfate, 24% S; sulfate of potash-magnesium, 22% S; potassium sulfate, 18% S; ammonium thiosulfate, 24% S; and gypsum, 18% S. Other sources may be available from local fertilizer dealers.
Farmers often express concern about using elemental sulfur or ammonium sulfate because of the amount of acidity these products generate. However, it takes very low rates of these materials to supply 15 to 20 pounds of sulfur per acre. The effect of such rates on soil pH is minimal.
The amount of lime required to neutralize the acidity formed by sulfur fertilizers would be around 100 pounds per acre for the recommended nitrogen rate. Most complete fertilizers containing ammonium generate more acidity than ammonium sulfate or elemental sulfur products.
The Agronomic Division of the N.C. Department of Agriculture and Consumer Services provides soil testing and plant tissue analysis. Both of these laboratory tests are useful tools for assessing a crops need for sulfur. There is no fee for soil testing, and tissue analysis only costs $4 per sample. For more information or assistance in collecting samples, call the division at (919) 733-2655.