Newer multi-trait soybean varieties have resulted in greater yields, bringing into question whether current soil test K (STK) correlation, calibration, and recommendations need updating to maximize yield. The objective of this study was to refine soil test correlation and calibration using a range in residual STK levels and response in temporal leaf and seed K concentrations and yield across soybean maturity groups IV and V. For the 0- to 15-cm soil depth STK levels greater than 125 mg K kg-1, K did not limit yield. Critical tissue K varied between years and maturity group. Critical K at R1, R3, and R5 for group IV soybean were 13.5, 13.2, and 12.9 g K kg-1, respectively and 12.9, 12.6, and 10.9 g K kg-1 for group V, respectively. Maintaining optimal STK levels can help ensure profitable and sustainable soybean production in Mississippi.