Diagnosing and Correcting Sulfur Deficiency in Crops
In recent years, sulfur (S) deficiency has been diagnosed in corn, soybean, alfalfa, and wheat in the Midwest including Indiana, according to Jim Camberato and Shaun Casteel, Agronomy Department, Purdue University. There are a number of reasons why S deficiency appears is becoming a more common occurrence, including reduced atmospheric S deposition, continued and increasing crop removal of S, greater use of no tillage, and high amounts of crop residues. It is wise to consider S deficiency when troubleshooting crop growth problems where yellowing of the crop is the primary symptom.
Sulfur deficient crops typically have an overall yellow appearance similar to N deficiency. However S is not as mobile in the plant as N, so lower leaves do not show more severe deficiency symptoms than the upper leaves. If a S deficiency is misdiagnosed as a N deficiency the application of fertilizer N will make the S deficiency worse, so tissue sampling is recommended to positively identify which nutrient is deficient. In corn, S deficiency may also cause leaf striping which is easily confused with magnesium, manganese, and zinc deficiency.
Correcting Sulfur Deficiency
Sulfur fertilizer should be applied as close to crop need as possible to reduce the chance it will be lost from the root zone by leaching. Often including S in a fertilizer program to avoid S deficiency is more efficient and less costly than correcting a S deficiency once it occurs. If S deficiency is anticipated in corn, an application rate of 15 pounds of SO4-S per acre is recommended on fine-textured soils and a rate of 25 pounds of SO4-S per acre is
recommended on coarse-textured soils, based on the most recent research conducted in Iowa. Although some carryover of S may occur in silt loam soils it likely will be necessary to make applications of S every year on sandy soils, particularly if irrigated and high yielding. Current research with soybean conducted by S. Casteel has found in-season soil and foliar applications of S to overcome S deficiency. Multiple foliar applications may be necessary to fully overcome S deficiency in some cases.