Plants need sulfur as it is part of some amino acids essential for optimum crop growth. Sulfur fertilization has traditionally been recommended only for soils of coarse texture (sandy soils) particularly after significant rainfall, or if there is a history of sulfur deficiencies. For years, air deposition (acid rain) was the main source of sulfur for plants, especially around heavily industrialized regions such as the Great Lakes area–even here in Arkansas we would get a good amount of sulfur every year. But air quality regulations have resulted in a considerable reduction of sulfur being deposited with rainfall. While this is a good thing for the environment, it has reduced the amount of plant-available sulfur from this source. The graph below shows approximate sulfate depositions in Arkansas for the last 30 years, as reported by the National Atmospheric Deposition Program (http://nadp.sws.uiuc.edu/NADP/). The graph clearly shows the decrease in depositions from a high of about 20 lb S-sulfate per acre in 1985 to only about 5 lb/acre for 2010.
So pay attention to potential deficiency symptoms and as you get ready to sidedress, consider including sulfur in your fertilization program, with about 75-100 lb/acre ammonium sulfate being enough to meet plant needs. For most crops, a deficiency appears as general chlorosis (yellowing). Sulfur is considered relatively immobile so symptoms will normally show in young leaves. Also, in crops where a large amount of nitrogen is applied at once, such as corn, an internal N:S imbalance may result in stunted plants that will start growing again as soon as sulfur is supplied.
Including sulfur in your fertility program may not be a bad idea.