Corn Response to Sulfur in Illinois.

Corn (Zea mays L.) response to sulfur (S) was first reported in Illinois over three decades ago but only in a few locations. Substantial increase in grain yield, S removal, and reduced atmospheric S deposition call into question the need for S fertilization. The objective of this study was to quantify the frequency and extent of corn response to S based on different soils and locations within Illinois. Eighteen small-plot trials and 22 on-farm strip-trials were conducted over three years. Five rates and several S sources were applied in small-plot trials while two rates were evaluated in on-farm strip trials as a pre-plant broadcast application. Sulfur increased yield only in two on-farm trials while no yield increase occurred in small-plot trials when analyzed by single location/year. However, a combined analysis across nine small-plot site-years showing a yield increase trend in the previous analysis revealed S increased grain yield. The agronomic optimum yield across these nine trials (12 Mg ha^-1 and 0.7 Mg ha^-1 above the check) was achieved with 42 kg S ha^-1. The soils at these trials had silt loam or coarser textured. Grain S concentration increased with applied S at three of 13 small-plot trials and at two on-farm trials. Sulfur products had no consistent effect on grain yield. Application of S increased soil sulfate concentration in the top 15 cm at six site-years and at five site-years in the 15-30 cm soil. Sulfur application did not influence soil S below 30 cm.  Overall, limited amount of S response likely relates to the fact that all tissue S and soil sulfate concentrations were within the sufficiency range.  The study highlights that while the frequency and magnitude of yield response to S seems to have increased since the late 1970’s, S fertilization is not a wide-spread need in Illinois.