Phosphorus Release and Speciation in Manganese(IV) Oxide and Zeolite-Amended Flooded Soils
Chammi P. Attanayake, Darshani Kumaragamage, Geethani Amarawansha, Ganga M. Hettiarachchi, Srimathie P. Indraratne, Douglas M. Goltz
Abstract
Phosphorus (P) losses from flooded soils and subsequent transport to waterways contribute to eutrophication of surface waters. This study evaluated the effectiveness of MnO2 and a zeolite Y amendment in reducing P release from flooded soils and explored the underlying mechanisms controlling P release. Unamended and amended (MnO2 or zeolite, surface-amended at 5 Mg ha–1) soil monoliths from four clayey–alkaline soils were flooded at 22 ± 2 °C for 56 days. Soil redox potential and dissolved reactive P (DRP), pH, and concentrations of major cations and anions in porewater and floodwater were analyzed periodically. Soil P speciation was simulated using Visual MINTEQ at 1, 28, and 56 days after flooding (DAF) and P K-edge X-ray absorption near-edge structure spectroscopy and sequential fractionation at 56 DAF. Porewater DRP increased with DAF and correlated negatively with pe+pH and positively with dissolved Fe. Reductive dissolution of Fe-associated P was the dominant mechanism of flooding-induced P release. The MnO2 amendment reduced porewater DRP by 30%–50% by favoring calcium phosphates (Ca–P) precipitation and delaying the reductive dissolution reactions. In three soils, the zeolite amendment at some DAF increased porewater and/or floodwater DRP through dissolution of Ca–P and thus was not effective in reducing P release from flooded soils.