Corn Response to Sulfur and Nitrogen Application Rates.

Due to earlier planting dates in cooler soils, increased nutrient removal by higher yielding cultivars, and reductions in atmospheric sulfur (S) deposition suggest that S application may require reassessment for optimal corn (Zea mays L.) growth.  In 2012 a field study was initiated on two soil textures to quantify corn response to S and to identify the influence S application has on nitrogen (N) use efficiency in Michigan corn production.  The study was arranged as a split-plot randomized complete block with four replications.  Main plots consisted of S rate (0, 22, and 45 kg S ha^-1) while sub-plots consisted of N rate (0, 56, 112, 168, 224, and 280 kg N ha^-1).  Sulfur applications were applied pre-plant incorporate while N applications were split with 40% of the N rate pre-plant incorporated and the remaining 60% N sidedressed to V6 corn.  Data collection included whole plant (V6), chlorophyll meter measurements (V6 and R1), greenseeker (V6), ear leaf (R1), stalk nitrate (R6), whole plant subsamples (R6), and yield (R6).  Significant yield differences were demonstrated between the 0, 22, and 45 kg S ha^-1 rates with no N application (6.7, 7.7, and 9.5 Mg ha^-1, respectively).  Significant yield differences were also observed between 0, 22, and 45 kg S ha^-1 when applied with 224 kg N ha^-1 yielding 9.0, 10.6, and 9.0 Mg ha^-1, respectively.  Results indicate S availability may not be sufficient in areas once classified as non-responsive to S application.  Supplemental S applications may have the potential to increase corn production without applying additional N fertilizer and simultaneously improve water quality through less overall N application.