Reducing soil phosphorus solubility with coal combustion by-products

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-l and Mehlich-III), water extractable P, and equilibrium P concentration (EPC0) of high P soils, Three widely available hy-products were used: fluidized bed combustion flyash (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.