At‐plant application of nitrogen effects on ultra‐late planted soybean behind corn in South Carolina

Abstract Over the last decade, corn ( Zea mays L.) and soybean [ Glycine max L. (Merr.)] commodity prices have fluctuated considerably and, more recently, increases in input prices have narrowed profit margins. Non‐traditional cropping systems that can boost profits are of increased interest to farmers in South Carolina, specifically double‐cropping soybean behind corn. Within this production system, soybean growth is limited due to inadequate environmental conditions, such as shorter day length, a shortened growing season, cooler temperatures, or premature frost. Applying at‐plant or close‐to‐planting applications of nitrogen fertilizer to ultra‐late planted soybean has been recommended in other states and explored by growers to increase overall final plant height (PH) and final height to first fruiting node (HFF) by increasing internode length during the vegetative growth stages to aid harvest efficiency. To determine the impact of an early application of nitrogen fertilizer on ultra‐late planted soybean, field studies were conducted in 2022–2024 to evaluate five different rates of ammonium nitrate (34‐0‐0)—0, 15, 30, 60, and 90 lb of N ac −1 —on soybean PH, HFF, and grain yield. Results from these studies showed no significant difference in soybean PH, HFF, or grain yield. However, partial profits were observed at 15 lb of N ac −1 , yet the lack of a significant difference makes these findings unlikely to yield a consistent return. Moreover, results from these studies indicate that the use of nitrogen, even in ultra‐late soybean production systems, does not increase overall plant growth or yield.