Corn response to sulfur fertilizer rate and source in Illinois

Sulfur (S) is an essential nutrient for optimizing corn (Zea mays L.) growth and yield. While S deficiency has increased in recent years, corn response to S fertilizer application remains challenging to predict owing to complex interactions among soil, crop, and weather conditions. Forty field trials were conducted between 2009 and 2011 over a range of soil types and environments to evaluate corn grain yield response to S fertilizer and assess the ability of soil and leaf S concentration to predict yield response to S fertilizer. Rate trials included two (0 and 34 kg S ha⁻¹) or five rates (0 to 52 kg S ha⁻¹, in 13 kg ha⁻¹ increments), whereas S sources were evaluated at 26 kg S ha⁻¹ (ammonium sulfate [21-0-0-24S], elemental S [0-0-0-90S], gypsum [0-0-0-21Ca-17S], monoammonium phosphate [MAP] MAP-10S [12-40-0-10S], MAP-10S+Zn [12-40-0-10S-1 Zn], and MAP-15S [13-33-0-15S]). Over the 3-year study period, we found minimal yield response to S fertilizer application with an overall response rate of 5% (two of 40 trials). In addition, neither S fertilizer evaluated increased corn grain yield relative to no S at any site; however, elemental S significantly reduced yield in one of 18 sites. While S application generally increased soil and earleaf S concentration, this did not translate into yield increases; hence, the lack of relationship between relative yield and soil and earleaf S. Under the study's conditions, these results indicate that S fertilization is unlikely to increase corn yields, and standard diagnostic tests such as soil S and earleaf S concentration are unreliable in predicting yield response in the upper US Midwest. Future research should incorporate other organic and inorganic soil S fractions to improve understanding and prediction of crop response to S fertilization.