Nitrogen fertilizer is an expensive input, and its necessity in grazed tall fescue (Schedonorus arundinaceus) pastures can be questioned when sufficient soil N mineralization occurs. A soil‐testing tool that could predict the need for N fertilizer inputs would be beneficial to producers to optimize profit and avoid environmental contamination. Thirty‐seven on‐farm trials were conducted in the Piedmont and Blue Ridge regions of Georgia, South Carolina, North Carolina, and Virginia in 2018 to evaluate fall‐stockpiled tall fescue yield response to N and P fertilizer inputs. Carbon and N characteristics of the soil surface (0‐ to 10‐cm depth) and surface residue varied among sites. Forage mass responses to P fertilizer input were below the economic threshold, regardless of Mehlich‐III extractable P. Forage mass responses to N fertilizer input did not exceed a low cost/value threshold of 5 kg forage kg−1 N in 24 of the trials. Economically optimum N rate was greatest when soil N mineralization and soil‐test biological activity (STBA) were at low levels. Results validated those of an earlier study on 55 fields, and taken together, suggest that N fertilizer for fall‐stockpiled tall fescue could be as high as 80 kg N ha−1 on fields with very low STBA (<100 mg CO2–C kg−1 soil 3 d−1) and declining to nil with medium STBA (>250 mg CO2–C kg−1 soil 3 d−1), depending on cost/value threshold. Healthy soils with high STBA can be managed effectively without N fertilizer inputs to recycle nutrients and promote more sustainable agricultural systems.