Alfalfa growers need to be aware of possible sulfur deficiency in their fields, says Jim Morrison, Ogle County, IL, Extension educator.
The problem has become more prevalent in recent years, says Morrison, due to less acid rain; 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 is most likely on low-organic-matter, coarse textured and eroded fine-textured soils, he says. 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 is not very reliable or useful, so a plant analysis is recommended. Sample the top 6” of plants at early bloom from several locations within a field. The samples can be collected prior to any cutting. The critical level for sulfur at this maturity stage is 0.22%.
When the need for sulfur has been established, 25-50 lbs/acre of sulfate sulfur will normally meet the requirement for a year or two. If elemental sulfur is applied at the same rate, it should last for the life of the stand.
Sulfur is an essential nutrient required in the formation of plant proteins and enzymes, says Morrison. “It is important in chlorophyll synthesis and required for nodulation and nitrogen fixation. Let plant analysis identify the sulfur status of your alfalfa, and then take appropriate action.”