Around Area Farms: Farmers must learn to manage sulfur in fields
Posted: 05/16/2013 at 7:01 am
Around Area Farms
Across the Midwestern Corn Belt, sulfur (S) deficiencies have been showing up in spotty areas. Corn, wheat and alfalfa are the crops most often shown to be deficient in sulfur.
Twenty years ago, sulfur deficiencies were almost unheard of. Efforts to reduce sulfur pollution from power plants have been successful. It is estimated that sulfur deposited by rain has dropped from about 8 pounds per acre in 1989 to 3 pounds per acre in 2009. That is a good thing. On top of that, crop yields have increased, so over time, sulfur has been mined from the soil. In the case of row crops, increases in no-till, early planting and heavy residue from high yields have also been implicated in contributing to S deficiency. We now have to learn how to manage sulfur in some fields.
Sulfur deficiency may be highly variable in a given field because soil S availability varies considerably with organic matter and texture. Sulfur deficiency is often seen in sandier, lower organic matter soils, or on higher elevation areas of a field, while lower lying, higher organic matter and more heavily textured areas have sufficient S.
Soil testing methods measure the sulfate form of sulfur. Unfortunately, soil testing is not particularly useful for predicting S deficiency because it does not take into account the organic S component that might become available to the crop. The sulfate component that is measured in a soil test may also be leached from the soil between the time of sampling and the time of crop need.
Sulfur deficiency is not easy to identify because it looks similar to many other plant ailments, including other forms of nutrient deficiencies and even potato leafhopper damage in alfalfa. The best way to identify a sulfur deficiency is by tissue sampling.
In alfalfa, for instance, collect the upper 6 inches of stem and leaf tissue from 40 to 50 plants from the area suspected of deficiency, and pull a sample from a healthy area of the field for comparison. If samples are contaminated by soil they can be rinsed quickly in cold distilled water, but do not overdo it because some nutrients, especially potassium, may be leached out of the tissue. Wet samples should be air-dried before shipping to the laboratory in paper bags. Tissue S greater than about 0.25 percent on a dry matter basis indicates the plant is sufficient in sulfur.
If S deficiency is identified, an application rate of 20 to 30 pounds of a sulfate-containing fertilizer per year is recommended to alleviate S deficiency in alfalfa based on the most recent research conducted in Iowa. Although some carryover of S may occur in silt loam soils with deep-rooted alfalfa crops, it may be necessary to make applications of S every year on sandy soils, particularly if the crop is irrigated and high yielding.
Jeff Burbrink is an Extension educator in agriculture and natural resources. Write to him at 17746 E. C.R. 34, Goshen, IN 46528; call 533-0554; or fax 533-0254.