Evaluation of soybean response to various sulfur fertilizer sources

Abstract Identifying optimal fertilizer‐sulfur (S) sources is crucial for effective soil‐S fertility management. The study evaluated soybean [ Glycine max (L.) Merr.] yield and tissue‐S concentration responses to five fertilizer‐S sources, ammonium sulfate, Sul4r‐Plus/Gypsum, K‐Mag, Tiger90CR, and Poly4, along with a no‐S check across 9 site‐years in Louisiana from 2023 to 2024. Each trial followed a randomized complete block design with four replications at 3 site‐years and five replications at 6 site‐years. Positive yield responses to fertilizer‐S were recorded at only Site‐Years 4 and 7, where soil‐S concentrations at 0‐ to 15‐cm depth were 9.1 and 12.0 mg kg −1 , respectively. At responsive site‐years, Tiger90CR significantly increased yield compared to no‐S check when applied at planting. Gypsum and K‐Mag also consistently increased yield when applied at the full‐flowering stage and showed the potential of boosting yield if applied at planting. Leaflet‐S concentrations at the full‐flowering stage align with the yield response from gypsum and K‐Mag treatments. Due to the limited number of responsive site‐years, it is challenging to identify a single fertilizer‐S source that consistently improves soybean yield. However, ammonium sulfate, the most used S source in Louisiana and other states, did not consistently enhance yield or leaflet‐S concentration in the responsive site‐years. Furthermore, the lack of leaflet‐S concentration increase for the preplant application of Tiger90CR at both responsive site‐years suggests that Tiger90CR may require time to dissolve and release S for plant uptake. Continued research on S sources is essential to identify the most suitable options for soybean production in the Deep South climatic conditions.