While the secondary macronutrient sulfur used to be adequately supplied through atmospheric deposition, times have changed, and we now receive almost zero sulfur via deposition.
Additionally, plant-available sulfur in the soil has been reduced by an estimated 34-86% over the last 20 years. This has led to sulfur deficiency symptoms in corn becoming more common.
Sulfur deficiency in corn is overall a lighter green plant color and chlorotic (yellow) stripes in between the veins (interveinal chlorosis) in the mid- to upper-crop canopy. These symptoms usually appear somewhere around V5 and will be persistent if sulfur deficiency is a problem for the plant.
Soil tests are not a reliable way to predict sulfur deficiency in Iowa soils. Generally, lower organic matter soils (less than 3.5%), sandy soils and those with eroded surfaces are most likely to need sulfur. But in more recent years, sulfur deficiency has appeared on higher organic matter and finely textured soils.