For soybean producers, K fertilizer is the costliest input; while under-fertilization can decrease seed yields, over-fertilization may not result in a yield increase. Our recent work at Edisto REC showed that over-fertilization of K can reduce soybean seed yields. Hence, from a producer’s perspective, finding the optimum K fertilizer application rates is vital. Moreover, despite being an immobile nutrient in the soils, K still leaches out of the root zone in sandy, low organic matter soils. These factors together make K of greater concern for South Carolina soybean producers. Hence, this project aims to determine optimum K fertilizer rates to maximize soybean yields and farm profits.

1. Evaluate the soybean yield response across five fertilizer-K application rates (0, 30, 60, 90, and 120 pounds K2O per acre) through on-farm trials.
2. Correlate the trifoliate leaf K concentration with soil test levels.

Outputs will be a better understanding of soybean potassium management and improve soybean profitability. The results from this study will be presented to extension agents and producers in field days and winter meetings. This will be the third and last year of the study. At the end of 2023, results will be compiled into an extension article made available for stakeholders and a short (< 5 minutes) YouTube video.

The ability of the potassium fertilizer applications to enhance growth and soybean yield will be quantified and analyzed at the end of the field trial. Economic cost/return sheets can be developed to determine how profitable the treatments are.

Soybean yields have increased substantially in recent decades due to better management of improved varieties. The question being asked is, “Are Clemson’s current potassium (K) fertilizer recommendations good enough to sustain high soybean yields?” In phase one, we conducted in-depth work at Edisto REC on evaluating K recommendations and plant analysis to optimize yield. In the second phase, we expanded this work in 2021 and 2022 to on-farm trials to verify if the results obtained at on-station trials are aligned with the results of on-farm trials. We want to continue on-farm trials with five more sites in 2023. This will help us create more robust datasets testing K fertility recommendations across production environments. The proposed research will generate new information to make Soybean production in South Carolina more productive and profitable.