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Reducing Soil Phosphorus Solubility with Coal Combustion By-Products

USDA-ARS, Pasture Systems and Watershed Management Research Laboratory, Curtin Road, University Park, PA 16802-3702.

^* Corresponding author (ws1{at}psu.edu).

ABSTRACT

In the northeast USA, most soil samples analyzed for soil test P (STP) in 1990 exceeded P levels needed for plant production. Converting soil P to less soluble forms with applications of materials containing lime or Ca may reduce the release of soil P to runoff. We investigated the effect of several coal combustion by-products on STP (Bray-1 and Mehlich-III), water extractable P, and equilibrium P concentration (EPC₀) of high P soils. Three widely available by-products were used: fluidized bed combustion fly ash (FBC), flue gas desulfurization by-product (FGD), and pulverized coal flyash (PC). In a by-product type and rate experiment, a Berks soil with high STP was incubated for 21 d with each by-product (0, 10, 20, 40, and 80 g kg soil^–1). The highest rates of FBC and FGD reduced Mehlich-III P (45%), Bray-I P (50%), water extractable P (72%) and EPC₀ (37%). The PC had no effect on soil P solubility due to the addition of P with this by-product. For eight soils ranging in physical and chemical properties, FBC at 10 g kg soil^–1 reduced Mehlich-III P 13%, and water-extractable P 71%, while FGD reduced Mehlich-III P 8% and water-extractable P 48%. These reductions resulted from the conversion of readily desorbable soil P to less soluble Ca-bound or Al- and Fe-bound pools. Amending high P soils with FBC or FGD by-products has the potential to reduce P enrichment of runoff by decreasing the solubility of soil P without reducing STP below optimum levels for plant growth.