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) K2O; and (c) 112 kg ha(-1) P2O5. 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.