The following is an excerpt from an article from Purdue University agronomists about sulfur deficiency in corn. Sulfur acts in some ways like nitrogen and like P&K in others. It can be easy to mistake sulfur deficiency for N deficiency, but with these helpful tips from Purdue, you can learn what to look for.
Sulfur Deficiency in Corn
By: Jim Camberato, Stephen Maloney, and Shaun Casteel Agronomy Department, Purdue University, West Lafayette, IN
Sulfur (S) deficiency has been diagnosed in corn and wheat in Indiana in recent years. More than half the corn S deficiency experiments conducted in northeast Iowa since 2005 have responded to fertilizer S. It is wise to consider S deficiency when troubleshooting corn growth problems.
Factors Affecting Sulfur Deficiency
Sulfur deficiency of corn and other crops may be becoming more prevalent because less S is deposited from the atmosphere to the soil due to reductions in power plant S emissions. In addition, increased yields over time result in greater crop S removal from the field. Corn grain contains about 0.5 pound of S for every 10 bushels of grain, so about 10 pounds of S per acre is removed by corn that yields 200 bushel per acre. Additionally, less incidental S applications in fertilizers and pesticides may contribute to more S deficiency. Increases in no-till, early planting, and heavy residue from high yields have also been implicated in increasing the occurrence of S deficiency.
Soil Factors Resulting in Sulfur Deficiency
The main source of S in most soils is organic S. Each percent organic matter in the plow layer contains about 100 pounds of sulfur per acre. Organic S must be mineralized to be taken up by crop plants, in much the same way that organic N is made available to crop plants. Therefore the lower the organic matter content of the soil the more likely S deficiency is to occur.
Sulfate-S is relatively mobile in most soils (similar to nitrate) because it has a double negative charge and is repelled by the negative charge of the soil, unlike nutrients such as potassium, calcium, or magnesium. Although SO4-S can bind to iron and aluminum in the soil, these elements are much more likely to bind phosphate at the exclusion of SO4-S. As a result, SO4-S is easily leached from soils, especially sandy soils.
Identifying Sulfur Deficiency in Corn
Sulfur deficient corn typically has 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. Young corn that is sulfur deficient may show striping as well as an overall yellow color.
Correcting Sulfur Deficiency in Corn
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, 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.
There are several fertilizers available for correcting a S deficiency. Adding ammonium thiosulfate to urea-ammonium nitrate solutions or blending ammonium sulfate with urea are convenient and cost effective ways to provide S in a timely manner. Sulfate-of-potash-magnesia (sul-po-mag or K-mag) or potassium sulfate can be blended with muriate of potash to provide S and K. The inclusion of magnesium in sul-po-mag may be an extra benefit compared to potassium sulfate if soil magnesium levels are low. Generally these fertilizers are spread prior to planting therefore the SO4-S might be lost from sandy soils before the time of crop need.