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.

Automated summary

This study investigated the different forms of phosphorus in soil after long-term application of broiler litter and ammonium nitrate. It was found that the use of broiler litter increased the extractable organic phosphorus content, but also led to the accumulation of organic phosphorus in soil. Soybean rotations and cover crops could help remediate phosphorus-laden soils after repeated application of broiler litter.