Effect of fertilizer source and rate on phosphorus leaching and extractable phosphorus in soils with long‐term dairy manure history

Land application of dairy manure is a common practice on dairy farms. Long‐term application of phosphorus (P), in the forms of manure or fertilizers, to cropland can lead to a buildup of P in the soil and increased soil test P. Understanding how additional manure inputs can influence P nutrient balances throughout agroecosystems in Connecticut is critical. Intact soil columns were collected from two hay and two corn ( Zea mays L.) fields with long‐term history of manure application. Separated liquid dairy manure (SLM) and granular P (GP) were applied to the surface of the soil columns at rates of 54, 108, and 161 kg P 2 O 5 ha −1 along with no fertilizer control. Columns received weekly irrigation to mimic average monthly rainfall in Connecticut. Leachate was collected across six sampling times during a 21‐week incubation following fertilization. P dynamics from soil and leachate were evaluated by measuring total P (TP), modified Morgan (MM) extractable P, MM‐Ca, and pH. Across most fields, there were no significant differences in TP, MM‐P, MM‐Ca, or pH across fertilizer source or application rate. Exceptions were greater TP leachate concentration in Corn Field 2 by GP, greater MM‐P increase by GP in Corn Field 1, and greater pH change by SLM in Corn Field 2. MM‐P and soil pH declined during incubation, while MM‐Ca increased. These results indicate that leachate TP and MM‐extractable nutrient responses were primarily driven by baseline soil properties, reflecting the legacy effects of historical management, throughout the incubation, rather than fertilization treatments alone.