Carryover Potassium

Optimal potassium (K) management requires considering fertilizer-K carryover. To offer general K management guidelines, we estimate summary carryover functions using meta-analysis, integrating them with estimates using data in USDA Ag Data Commons. Using dynamic programming we demonstrate that accounting for carryover increases fertilizer-K recommendations and profitability. Fertilizer-K carryover is estimated at roughly 20–30%. Considering carryover is much like reducing the effective price of K in the current year, ignoring it underestimates fertilizer-K recommendations. Since soil-K reserves may slowly supply or retain K but are not captured by routine soil testing, the true optimal fertilizer-K rate may be even higher.