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

Abstract

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 P₂O₅ 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.