Runoff Phosphorus Losses as Related to Phosphorus Source, Application Method, and Application Rate on a Piedmont Soil

Land application of animal manures and fertilizers has resulted in an increased potential for excessive P losses in runoff to nutrient‐sensitive surface waters. The purpose of this research was to measure P losses in runoff from a bare Piedmont soil in the southeastern United States receiving broiler litter or inorganic P fertilizer either incorporated or surface‐applied at varying P application rates (inorganic P, 0–110 kg P ha −1 ; broiler litter, 0–82 kg P ha −1 ). Rainfall simulation was applied at a rate of 76 mm h −1 Runoff samples were collected at 5‐min intervals for 30 min and analyzed for reactive phosphorus (RP), algal‐available phosphorus (AAP), and total phosphorus (TP). Incorporation of both P sources resulted in P losses not significantly different than the unfertilized control at all application rates. Incorporation of broiler litter decreased flow‐weighted concentration of RP in runoff by 97% and mass loss of TP in runoff by 88% compared with surface application. Surface application of broiler litter resulted in runoff containing between 2.3 and 21.8 mg RP L −1 for application rates of 8 to 82 kg P ha −1 , respectively. Mass loss of TP in runoff from surface‐applied broiler litter ranged from 1.3 to 8.5 kg P ha −1 over the same application rates. Flow‐weighted concentrations of RP and mass losses of TP in runoff were not related to application rate when inorganic P fertilizer was applied to the soil surface. Results for this study can be used by P loss assessment tools to fine‐tune P source, application rate, and application method site factors, and to estimate extreme‐case P loss from cropland receiving broiler litter and inorganic P fertilizers.