Reducing Soil Phosphorus Solubility with Coal Combustion By‐Products

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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.

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