Corn Grain Yield Response to Sulfur Fertilization in Indiana

Reduction in sulfur deposition from power plant emissions has resulted in lower amounts of soil sulfur and, perhaps, in inadequate sulfur availability for corn. The objective of this study was to determine if corn (Zea mays L.) grain yield was responsive to S fertilization in Indiana and what soil and cropping system factors contributed to the likelihood of a response. Field scale experiments were conducted at 28 sites from 2017 to 2020, the majority in corn-soybean (Glycine max (L.) Merr) rotation. In-season measurements included soil sulfate-S concentration and soil texture from 0 to 60 cm in 20 cm increments, plant nutrient concentration in the whole plant at V3-V7, in the earleaf, and in the grain. Additional measurements were 1,000 kernel dry weight, total kernel rows per ear, and kernels per row. Sulfur treatment rates ranged from 0 to 34 kg S ha-1 as ammonium thiosulfate, and were applied as starter, sidedress, and both combined. Fertilizer S increased grain yield by 0.2 to 3.0 Mg ha-1 at 10 of 28 Indiana site-years, approximately a 36% frequency of response. When a response to S fertilizer occurred, the lowest sidedress rate examined in that site-year, which ranged from 8 to 17 kg S ha-1 , was enough to maximize grain yield. On soils with 26 to 31 g kg-1 OM, S fertilization increased yield 0.2 to 0.3 Mg ha-1 at 2 of 10 site-years. Response to S fertilization at 8 of 10 site-years with soils with lower OM, 10 to 25 g kg-1 , had higher yield increases ranging from 0.7 to 3.0 Mg ha-1 . Grain yield responses occurred in both coarse- and fine-textured soils and were consistent and large at 2 sites. Sulfate-S concentration in the soil and S concentration in the whole plant (V4-V7) were not good indicators of response to S fertilization. For the majority of the site-years where grain yield increased with S fertilization, the grain S concentration, earleaf S concentration, and earleaf N:S were respectively <0.9 g kg-1 , <1.8 g kg-1 , and >15:1 without S treatment. These parameters improved with the addition of S but some site-years with these values did not have a yield response. These earleaf S and N:S ‘critical values’ may serve as reference for potentially S responsive sites, but more observations are necessary to validate these critical levels. Sites with higher basal values (without fertilizer treatment) for earleaf and grain S concentration and lower earleaf N:S still showed increased tissue S concentration upon S fertilizer application, albeit with no increase in grain yield. We encourage farmers to consider S fertilization at rates ranging from 8 to 17 kg S ha-1 applied at sidedress. this recommendation for fields showing S deficiency symptoms or where R1 earleaf S concentration and N:S are below 1.8 g kg-1and above 15:1, respectively.