Soybean Response to Sulfur Fertilization and Placement.

Earlier planting dates, reduced early season nutrient mineralization, increased nutrient removal, and reductions in atmospheric S deposition have increased concern regarding early season sulfur (S) availability for optimal soybean (Glycine max L.) growth.  A field study was established to determine the effects of 28 kg S ha^-1 with or without a starter fertilizer of 22 kg nitrogen (N) ha^-1 and 56 kg phosphorus (P) ha^-1 on soybean yield and quality.  The study was arranged as a split- plot randomized complete block design with four replications.  Main plots consisted of S timing (no S, pre-plant incorporate, at planting in a 5x5 cm band, and split between a band at planting and sidedress at R1) while the sub-plot consisted of N and P fertilizer applied at planting (with or without in a 5x5 cm band).  Data collection included SPAD measurements (V4 and R1), petiole samples (R1), root nodule counts (R3), soil samples (R3), grain oil, protein, and yield (R8).  Early season SPAD measurements indicated the application of starter significantly increased plant greenness compared to no starter, 0.98 and 0.94 % of optimal, respectively.  Yield data show S applied as pre-plant incorporate without starter demonstrated a significant increase compared to plots where S was applied at planting without starter, 3.1 vs. 2.4 Mg ha^-1, respectively, however, treatment yields were not significantly different from the check, 2.8 Mg ha^-1.  Results for grain oil and protein were not significantly different among each treatment, but results suggest the application of S and starter significantly increased grain oil and protein levels as compared to no application. First year preliminary data suggest applying S may not be necessary to increase soybean yield for Michigan fields testing 6 mg S kg^-1 or greater, but S and starter fertilizer applications may improve early plant color and seed quality.