Sequential P Extracts in Cecil Soil During Ten Years of Conventional and Conservation Tillage Cropping Management with and without Poultry Litter.

Soil phosphorus (P) buildup from long-term applications of poultry litter presents a potential environmental problem. Knowledge of soil P distribution among its chemical forms is useful for assessing risk levels. We measured sequentially-fractioned H₂O, NaHCO₃, NaOH, and HCl extractable P in a Cecil soil from 1996 to 2005 near Watkinsville, GA, from samples taken in the second of a 5-yr cotton phase, at the end of the cotton phase, and at the end of a 5-yr corn phase following cotton. Each crop was managed in either conventional tillage or no-till, with either conventional fertilizer (CF) or poultry litter (PL). Rye was the winter cover crop. For cotton, PL application rate was 4.5 Mg ha^-1 based on nitrogen (N) requirement. For corn, PL application rates were 2 to 4 times that of cotton, partly because of corn’s greater N requirement. Inorganic P fractions extracted were 53 to 79%, with NaOH, 16 to 22% each with NaHCO₃ and HCl, and < 5% with H₂O. Total P (Pt) fractions extracted were 60 to 80% with NaOH, 15 to 23% with NaHCO₃, 3 to 18% with HCl and < 5% with H₂O. The residue fraction accounted for 23 to 43% of Pt. With conventional fertilizer, P fractions remained essentially the same throughout or slightly increased (~ x 2) by October 2005. With PL, fractions essentially remained the same during cotton but increased 2 to 5 times by October 2005. Sequentially, total P in mg kg^-1 from the PL fields in October 2005 was approximately 17, 85, 214, 61, and 114 for H₂O, NaHCO₃, NaOH, and HCl extracts and residual, respectively. In Cecil soil, application of PL at levels to meet N needs of corn increases the risk of increasing soil P to environmentally unacceptable levels.