Total Phosphorus, Zinc, Copper, and Manganese Concentrations in Cecil Soil Through 10 Years of Poultry Litter Application

Poultry litter (PL) is an inexpensive and effective source of plant nutrients. However, overapplication could result in phosphorus (P) and heavy metal accumulation in soils. A field experiment evaluating PL application to a Cecil soil used for cotton and corn production has been maintained for 10 years. At the end of the cotton phase (i.e., the first 5 years), PL annually applied at 4.5 Mg ha(-1) did not increase concentrations of total soil P, zinc (Zn), Cu, or manganese. During the corn phase (i.e. the second 5 years), PL application rates were increased from two to four times that used for cotton partly because of corn's greater N demand. With this change, the average total P in the surface 15-cm soil nearly doubled to about 560 mg kg(-1) of dry soil in both conventional till and no-till fields at the end of the corn phase. During the same time, Cu increased from 7 to 22 mg kg(-1) and Zn increased from 17 to 32 mg kg(-1) of dry soil. Levels of manganese were basically unchanged. Total P and Cu also increased in the 15- to 30-cm depth, with concentrations in the 0 to 15 cm being 1.8 to two times that in the 15 to 30 cm for P and approximately two times for Cu. Relationships between extractable versus total P and Zn changed at a threshold point beyond which extractable P and Zn increased at more than double the initial rate. It seems that once accumulation of P and Zn exceeded the soil buffer capacity nutrient availability was significantly altered. Therefore, close monitoring of soil nutrients especially P is essential to avoid over application of PL that may potentially pose environmental risks for water Pollution.