Phosphorus and Metal Distribution in Soil Aggregate Fractions from Poultry Litter Applied Soils.

Poultry litter application in agricultural lands as a source of fertilizer is of high environmental concern due to the risk of phosphorus (P) overloading and thereby P run-off from soils to water-ways. In addition, recent studies indicate addition of poultry litter may have an effect on overloading of trace metals in soil over time since significant amount of trace metals are incorporated in poultry feed. Soil aggregate fractions play an important role in determining P and metal sorption/release from soils. The P and trace metals bound to fine soil fractions are believed to have impact on water quality since the fine soil fraction is preferentially transported to surface water through run-off and wind-erosion.  However, little information is available on effect of long-term manure application on distribution of P and metals in soil aggregates, and the role of metals on sorption/release of P from such fractions. The objective of this study is to investigate the effect of poultry litter application in agricultural soils on P and trace metal distribution in soil aggregate fractions. Soil aggregate fractions (2.0 mm, 1.0 mm, 0.5 mm, 0.25 mm, 0.125 mm, and 0.053 mm ) for this study was obtained by dry sieving surface soils (0-15 cm) collected from a long-term poultry litter applied Decatur silt loam soil at three N rates (0, 100, and 200 kg N ha^-1) under different tillage systems. Aggregate fractions were analyzed for DTPA extractable metals, Mehlich 3 extractable P/metals, and total P/metals. Sequential fractionation of P and metals in aggregate fractions were carried out to identify the distribution of different forms of P and metals in each fraction. Some variations in P and metal distribution were observed in different size aggregate fractions.