Legacy phosphorus in Alabama Hartsells soil after long-term amendment with broiler litter

Numerous studies have investigated effects of long-ter m manure application on total phosphorus (P) and inorganic P (P-i), but few have evaluated soil organic P (P-o). Little is known about crop management effects on Po in soils with varying minerology. In this study, sequential fractionation was used to characterize specific P forms after 25 years of broiler litter (BL) or ammonium nitrate (Con) applications to an Alabama Hartsells soil. Crops (corn [Zea mays L.], soybean [Glycine Willd.], and corn or soybean with a wheat [Triticum aestivum L.] cover crop) were under conventional tillage (CT) or no-tillage (NT). Regardless of crop, tillage, or fertilizer type, the proportion of extractable P-i was relatively stable at 21%-49% at 0-5 cm and 25%- 45% at 5-10 cm. Extractable Pi ranged from 0.69 to 2.4 mg g(-1). BL increased total extractable P-i (p = 0.001) at 0-5 cm and 5-10 cm. Total extractable P was influenced at 0-5 cm (p = 0.006) by both tillage and fertilization type, but not at 5-10 cm or at either depth in soybean plots. Long-ter m BL application increased total extractable soil Pat 0-5 cm. In corn systems, CT did not reduce P loading to topsoil or result in P leaching to lower soil depths, compared to NT. Soybean and soybean-wheat reduced P loading in BL plots, compared to corn and cor n-wheat. Soil Po was classed in the order of monoesters > phytate and polyphosphates, where most was extractable with NaOH. BL increased extractable P-o in all fractions. Care should be taken when apply-ing BL to highly weathered soils to avoid legacy Po accumulation. Soybean rotations and cover crops could help remediate P-laden soils after repeated BL application.