Corn and soybean response to dry versus liquid phosphorus and potassium fertilizers

Abstract Interest in liquid phosphorus (P) and potassium (K) fertilizers is increasing, often with claims of superior performance over dry‐granular sources. We compared yield and tissue‐nutrient responses of corn ( Zea mays L.) and soybean [ Glycine max (L.) Merr.] to dry versus liquid P and K. Field trials were conducted from 2021 to 2024 across 42 site‐years, including eight corn and six soybean sites, with separate P‐only, K‐only, and combined P+K trials for each crop. Each trial included a no‐fertilizer check and factorial combinations of source (dry vs. liquid) and rate (half vs. full). Triple superphosphate and muriate of potash were dry‐fertilizer sources, and ammonium polyphosphate and Nachurs K‐fuel were liquid‐fertilizer sources. Leaf nutrients were analyzed at V11–V12 (corn) and R2–R3 (soybean) stages, and yield was measured at maturity. In P‐ or K‐deficient soils, corn yield did not differ by sources; however, full‐rates increased yield by 5%–13% over half‐rates. For soybean, source and rate effects were not significant in single‐nutrient trials, whereas in P+K trials, full‐rates increased yield by 9%–10% over half‐rates. Across environments, yield responses aligned with tissue diagnostics; tissue‐K was consistently associated with yield gains, whereas tissue‐P was less predictive under common luxury P uptake. Overall, liquid sources provided no advantage over dry‐granular sources at equivalent rates. Half‐rate liquid did not match full‐rate dry yields, and co‐applied P+K mirrored single‐nutrient responses; yield differences reflected rate, not formulation or synergy. Results emphasize using soil‐test‐based rates, not formulation, when targeting yield, and tissue‐K as a more reliable in‐season indicator of crop response than tissue‐P.