Can soil biology tests improve phosphorus and potassium corn fertilizer recommendations?

Integrating soil health (SH) biological properties with soil fertility (SF) evaluations offers a unique opportunity to potentially refine fertilizer recommendations. The objectives of this research included: (a) evaluating current University of Missouri P and K fertilizer recommendations for corn ( Zea mays L.) and (b) assess whether SH biological indicators are effective predictors of yield response to P and K fertilization. In Missouri, 446 monitoring sites (148 m 2 ) were implemented on 101 production corn fields over the 2018–2020 growing seasons. For each monitoring site, SH and SF samples were collected prior to planting, followed by application of nonreplicated single‐rate fertilizer treatments: (a) unfertilized control; (b) 112 kg ha –1 K 2 O; and (c) 112 kg ha –1 P 2 O 5 . At monitoring sites below recommended critical soil test values, P ( n  = 152) and K ( n  = 86) fertilization increased yield at 42 and 36% of the sites respectively, with average yield increasing 10 and 11% for P and K, respectively. At the lowest fertility ratings, P and K fertilization increased yield at 52 and 56% of sites, respectively, highlighting inherent uncertainty within current recommendations. Integrating SH with SF indicators failed to improve random forest algorithms prediction of yield increases from P or K fertilization. Further, variable importance ranking confirmed that current physiochemical SF tests remain the most effective factors identifying when a fertilizer response will likely occur. Although SH metrics may offer insight into other agronomic or environmental benefits, established SF evaluations remain the most effective available tool for guiding P and K fertilizer decisions in Missouri corn production.