Influence of redox potential on phosphorus solubility in chemically amended wetland organic soils

Abstract

Conversion of agricultural lands to wetlands results in solubilization of residual fertilizer P, thus increasing soluble P concentration of floodwater. Previous studies have shown that application of chemical amendments such as alum, FeCl 3 and CaCO 3 were found to be effective in decreasing soluble P of the soil porewater. Water-table fluctuations and variable hydraulic loading rates in wetlands can alter soil redox conditions, and the solubility of P compounds. The objective of this study was to determine the influence of oxidized and reduced soil conditions on P solubility of a wetland organic soil amended with chemicals. Soil treatments evaluated include: (i) control, (ii) CaCO 3 at 15.3 g kg −1, (iii) alum at 14.5 g kg −1, and (iv) FeCl 3 at 1.8 g kg −1. Dissolved reactive P of soils in the control and FeCl 3 amended soils responded to changes in Eh, while a less pronounced effect was noted in alum and CaCO 3 amended soils. Overall, dissolved P concentrations were higher under reduced conditions and decreased with increase in Eh. The KCl-P (labile inorganic P) decreased with increase in Eh, while NaOH-RP (Fe- and Al-bound P) increased with Eh, especially in control, FeCl 3 and alum amended soils. Soil amended with CaCO 3 showed minimal changes in either KCl-RP or NaOH-RP. In CaCO 3 amended soil, the solubility of P was regulated by the solid phases of Ca-P compounds, while in other treatments solubility was controlled by variscite, strengite, and vivianite. Amendments (such as CaCO 3 and alum) that are less sensitive to changes in redox conditions may be suitable for binding P under wetland environments.