Soybean response to potassium, magnesium, and sulfur fertilization on Southeastern Coastal Plain soils

Potassium (K), magnesium (Mg), and sulfur (S) are susceptible to leaching in Southeastern Coastal Plain soils and can limit crop production if not properly managed. This study aimed to determine the effect of K, Mg, and S fertilization on soybean [Glycine max (L.) Merr.] yield, tissue nutrient concentrations, and soil K, Mg, and S concentrations. Treatments included three K, two Mg, and two S fertilizer rates arranged in a randomized complete block design with three replications. There was no significant main or interaction effect of K, Mg, and S on soybean yield, even when the initial soil-test S level was below critical levels. Leaf K concentrations of control plots measured at the R2 growth stage were in the sufficiency range reported for soybean in southeastern states. However, leaf Mg and S concentrations were below the sufficiency ranges. Applying S fertilizer increased leaf Mg and S concentrations, but Mg fertilizer did not affect leaf Mg concentrations. Applying K fertilizer rates increased soil-test K across three soil depths compared to the control K treatment. The application of Mg fertilizer increased soil-test Mg more at 0-15 cm than at the other two depths (15-30 or 30-45 cm), whereas S fertilizer application increased soil-test S more at 15-30 cm. The soil samples taken before experiment initiation showed that the lower two soil depths had greater soil-test K and S concentrations than at the top layer. These findings indicate that more research is needed to appropriately credit subsoil nutrients while making fertilizer recommendations for soybean grown on Southeastern Coastal Plain soils.