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.
1United States Department of Agriculture-Agricultural Research Service, New England Plant, Soil, and Water Laboratory, Orono, ME 04469. Dr. He is corresponding author. E-mail: Zhongqi.He@ars.usda.gov
2United States Department of Agriculture-Agricultural Research Service, J. Phil Campbell, Sr, Natural Resource Conservation Center, Watkinsville, GA.
Received July 27, 2009.
Accepted for publication September 25, 2009.
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