From the Fields
Alfalfa growers need to be aware of possible sulfur deficiency in their fields. The sulfur input amount has changed over the years including less atmospheric sulfur deposition (due to the Clean Air Act of 1970), less incidental sulfur in fertilizers, insecticides, and fungicides, greater removal rates by increasing grain yields, and less manure application resulting from fewer livestock operations.
Since soil organic matter is the primary source of sulfur, a deficiency could be expected on low organic matter soils, coarse textured soils, and eroded fine textured soils.
Alfalfa suffering from sulfur deficiency will have a light green, yellowish coloration of the whole plant, stems could be spindly with weak growth, and plants could exhibit reduced nodulation and be stunted with less shoot development.
Because sulfur is highly mobile in the soil, a soil test for sulfur is not very reliable or useful, rather a plant analysis is recommended. Sample the top six inches of plants at early bloom from several locations within a field. These samples can be collected prior to any cutting. The critical level for sulfur at this maturity stage is 0.22 percent.
When the need for sulfur has been established, 25 to 50 pounds per acre of sulfate-sulfur will normally meet the requirement for 1 to 2 years. If elemental sulfur is applied at the same
rate, it should last for the life of the stand.
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