Fertilizer Source and Timing Affect Soil Profile Sulfur Dynamics in a Corn–soybean Rotation

Abstract Sulfur (S) deficiency is a relatively new concern for farmers in industrialized nations due to the decline of atmospheric S deposition in recent decades. Sulfur is mobile in the soil but can be retained in subsoil where it is adsorbed to iron (Fe) and aluminum (Al) oxyhydroxides and aluminosilicate clays, leading to stratification with depth. In this experiment, we evaluated the effectiveness of S fertilizers in a corn ( Zea mays L.)–soybean ( Glycine max L.) rotation, how S concentration varies with depth through time, and how soybean rooting depth interacts with soil profile S distribution. We applied S at a rate of 45 kg ha −1 as gypsum, ammonium sulfate (AMS), poultry litter, or elemental S to corn in the rotation and found that corn yield was similar to an untreated control (10.1 Mg ha −1 mean). We collected 80‐cm soil samples, which revealed increased S in subsoil layers after corn harvest and before soybean planting. During the soybean year of the rotation, we applied the same rate of S using gypsum and AMS to plots that were untreated during the corn year of the rotation. Soybean rooting depth reached the soil profile layers with the highest S concentrations by the R1 growth stage. Soybean yield was unaffected (2.7 Mg ha −1 mean), but grain S and cysteine concentrations increased with S fertilization, whether applied in the corn or soybean year. Results of this study support the development of flexible and economical S fertilization programs spanning multiple years by taking advantage of S storage in the soil profile.