Abstract Potassium (K) deficiency is one of the most important yield‐limiting factors in soybean Glycine max (L.) Merr. production. Recent research established the dynamic critical tissue‐K concentration curve for soybean, allowing accurate diagnosis of K deficiency during soybean reproductive growth. Potassium deficiency can be corrected with minimal yield loss if addressed in a timely manner. However, the site‐specific rate of fertilizer‐K needed to correct the deficiency remains unclear. Our research objective was to develop a calibration curve to predict the fertilizer‐K rate needed to correct varying levels of deficiency at 15, 30, and 45 days after first flower (DAR1). Thirteen site‐years of irrigated small plot research were conducted in Arkansas using the uppermost fully expanded trifoliolate leaf samples to measure the level of deficiency and assess the yield response to corrective applications of 0–149 kg K ha −1 at 15, 30, and 45 DAR1. As expected, severe deficiencies required higher rates of fertilizer‐K. Linear plateau models were significant ( p < 0.05) for each timing, and the slopes did not differ. Therefore, the aggregated slope and the join point, representing the leaf‐K concentration at which point no corrective fertilizer‐K is recommended, for each DAR1 can be used to predict the fertilizer‐K rate needed from 15 to 45 DAR1. Overall, the ability to receive a site‐specific, calibrated fertilizer‐K rate will enable producers to diagnose and correct K deficiency from 15 to 45 DAR1, extending from flowering through pod fill stages.
Ortel et al. (Sun,) studied this question.