There are 16 essential elements for a plant's growth and development. How growers manage and apply those elements affects yield, and ultimately their pocket books. The top three — nitrogen (N), phosphorus (P) and potassium (K) — are often managed and applied in starter fertilizers. But recently sulfur, previously considered a secondary nutrient, has had a significant impact on yields when added to starter fertilizers.
Since the passage of the Clean Air Act sulfate levels precipitated from the atmosphere have decreased by as much as 75%. This reduction, along with the use of more concentrated phosphate fertilizers and the reduced use of sulfur-containing crop protection chemicals, has put sulfur on the list of primary nutrients.
Sulfur is vital to a plant's growth in the production of amino acids and proteins. Low sulfur availability is related to low soil organic matter, sandy textures, low soil temperatures and erosion, says Larry Murphy, president of the Fluid Fertilizer Foundation. “Sulfur needs to now go beyond sandy soils.”
Murphy says organic matter doesn't release much sulfur over the winter and winter precipitation can move sulfur from the seedling area.
“Stress, cold soil temperatures, compaction, excess water and reduced tillage increase the need for sulfur in starter fertilizers,” Murphy says.
Barney Gordon, Kansas State University agronomist, sees cold soil temperatures having a big impact on available sulfur levels. “Planting dates are pushed earlier and earlier across the Corn Belt. And anytime you plant in cool conditions you can experience a deficiency of elements,” he says.
According to the Fluid Fertilizer Foundation, plants deficient in sulfur look similar to N-deficient plants. They are small and spindly with short, slender stalks. Plants also have a slower growth rate, delayed maturity and leaves are light green to yellow in color. The color effects appear first at the top of the plant, unlike N deficiencies, which appear first on the lower leaves.
“We do get a significant response when we add sulfur in our starter fertilizers,” says Gordon. Test plots have shown as much as a 10-15 bu./acre response to the addition of sulfur in a pre-plant starter fertilizer. And the rates Gordon uses are fairly low, not more than 10 lbs./acre of sulfur.
“It's pretty easy to add sulfur into a starter mix,” says John Clapp, director of agronomy research and development with Tessenderlo Kerley, makers of sulfur-based liquid fertilizers.
“The reductions in sulfur sources, combined with crop yield responses, indicate that a significant opportunity to increase quality and yield is missed when sulfur is not added to your starter fertilizer,” Clapp adds. “And the decline in atmospheric sulfur is expected to continue.”
| Fertilizer Treatment | Yield (bu./acre) |
|---|---|
| Unfertilized check | 137 |
| Nitrogen | 187 |
| Nitrogen + Phosphorus | 243 |
| Nitrogen + Phosphorus + Potassium | 256 |
| Nitrogen + Phosphorus + Potassium + Sulfur | 265 |
| SOURCE: BARNEY GORDON, KANSAS STATE UNIVERSITY | |