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

Numerous studies have investigated effects of long-term 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 P _o 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 P _i 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-term BL application increased total extractable soil P at 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 corn-wheat. Soil P _o 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 applying BL to highly weathered soils to avoid legacy P _o accumulation. Soybean rotations and cover crops could help remediate P-laden soils after repeated BL application.
(Published 2023. This article is a U.S. Government work and is in the public domain in the USA. Journal of Environmental Quality published by Wiley Periodicals LLC on behalf of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)