Soybean yield response to sulfur and nitrogen additions across diverse U.S. environments

As soybean [Glycine max (L.) Merr.] yields reach record highs, more nutrients are required to maintain these production levels. This study was conducted to evaluate the effect of S and N on soybean yield in diverse environments across the United States. Data were collected from a total of 52 sites in 10 states over 2 yr (2019 and 2020) for this study. A factorial arrangement of three S rates (11, 22, and 33 kg S ha⁻¹) using two sources (ammonium sulfate [AMS] and calcium sulfate [CaSO₄]) were broadcasted by hand at planting. Additionally, to examine the impact of N on soybean yield, urea was applied at 10, 20, and 29 kg N ha⁻¹ to equal that supplied by AMS. A zero-fertilizer control treatment was also included. Soil samples prior to fertilization as well as grain yield at R8 were collected and analyzed to understand what environmental conditions favor soybean response to S additions. Results indicated that soil and environmental factors are poor indicators of yield response to S and N additions. Yield responses to S and N additions were observed in yield environments averaging >3,643 kg ha⁻¹, but S did not limit yield in most environments (n = 49). Partial profit analysis was conducted at two soybean grain prices (US$0.32 and $0.55 kg ha⁻¹). Yield increases were only profitable at 2 site-years at the tested soybean grain prices. Overall results suggest that use of N and S fertilizers are rarely justified across diverse growing environments.