2025 article
Effect of model choice on critical soil test value of phosphorus for corn in long‐term trials in North Carolina
Filippi, D., Gatiboni, L., Crozier, C., Osmond, D., & Hardy, D. (2025, July 1). Soil Science Society of America Journal, Vol. 89.
open access via acsess.onlinelibrary.wiley.com (publisher PDF)Abstract The soil test correlation determines the critical soil test value (CSTV) of phosphorus (P) required to achieve 95%–100% of the maximum crop yield. However, CSTV predictions vary with the mathematical model used, which has implications for fertilizer recommendations. This study compared the P CSTVs for corn ( Zea mays ) estimated using four models, (1) modified arcsine‐log calibration curve (ALCC), (2) linear plateau (LP) at the join point (JP), (3) quadratic plateau (QP) at the JP (QP‐JP), and (4) QP at 95% of maximum yield (QP‐95), and then calculated the frequency of crop response at different Mehlich‐3 soil test phosphorus (STP) concentrations. Corn was grown in long‐term trials in 2010, 2012, and 2014 in the Piedmont, Coastal Plain, and Tidewater regions of North Carolina. The P CSTVs obtained with ALCC, LP‐JP, QP‐JP, and QP‐95 models were 42, 24, 31, and 26 mg kg −1 , respectively, at the Coastal Plain site and 55, 43, 55, and 49 mg kg −1 at the Tidewater site, but these models could not calculate CSTVs at the Piedmont site. Nevertheless, the 95% confidence interval of CSTV did not differ for these models and sites analyzed. The frequency of corn response to STP declined with increasing STP, reaching 10% at 37.0 and 44.9 mg kg −1 at Coastal Plain and Tidewater sites, respectively, defining critical soil test range (CSTR) of 26–37 and 45–49 mg kg −1 . Additional approaches combined with CSTV using broader datasets may help to refine the CSTR definition and improve fertilizer recommendations.