This study was conducted to measure season‐long uptake of P by corn grown under no‐till and conventional‐till management at three levels of P supply‐low, adequate, and high as defined by grain yield‐to test the feasibility of using whole‐plant P uptake as an indicator of the P supply in soil; and to calibrate soil P extractable with both Mehlich No. 1 (HC1 + H2SO4) and Mehlich No. 2 (HC1 + H2SO4+ NH4F) versus whole‐plant P uptake over the response region.