Date of Award

12-2023

Degree Type

Report

Degree Name

Master of Science (MS)

Department

Plants, Soils, and Climate

Committee Chair(s)

Paul Grossl

Committee

Paul Grossl

Committee

Grant Cardon

Committee

Melanie Stock

Abstract

Phosphorus (P) is considered immobile in calcareous soils. Organic matter is known to enhance P mobility in these soils. Few studies have considered what role iron oxides might play in P sorption in calcareous soils, especially in the presence of soluble organic matter. This study investigated P sorption dynamics in sand-based, simulated soil systems in the absence or presence of 5 mM carbon (C) as humic acid (HA). Treatments included combinations of dicalcium phosphate dihydrate (DCPD), calcite, and ferrihydrite. Solutions containing 10 mg P L-1 in a background of 0.01 M CaCl2were equilibrated with each solid treatment (solution:solid ratio = 33.3:1). Slurries were maintained at pH 7.5 and solutions were sampled over time and analyzed for orthophosphate-P. Humic acid inhibited P sorption in the systems where P solution activities were regulated by the solubility of Ca phosphates and no ferrihydrite was present. Humic acid did not inhibit P sorption in systems containing ferrihydrite. Zero valent iron (ZVI) is used as a sink for phosphorus in industrial and municipal water purification systems, but studies investigating its behavior on phosphate sorption in calcareous soils and how it may affect plant growth are scant. Oxidation of zero valent iron in calcareous soils results in the formation of a high surface area iron oxide like ferrihydrite which has a tremendous adsorption capacity for phosphate, where adsorption is rapid and not inhibited by organic matter, thus rendering P unavailable and immobile. Treating a calcareous soil, excessively amended with organic matter, with zero valent iron can significantly reduce levels of bioavailable P, potentially reducing the threat of receiving water quality deterioration and eutrophication.

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