Master of Science (MS)
Plant, Environmental Management and Soil Sciences
Loss of phosphorus (P) from soil may degrade water quality. The problem exists where soil has been heavily fertilized with P, including use of poultry litter as fertilizer for pastures on the Coastal Plain. This research proposed that amending a P-enriched soil with a material that has a relatively high capacity to sorb P would decrease such loss in runoff or subsurface drainage. The P sorption behavior of two adsorbent materials, naturally occurring soil ironstone and bauxite refining residue (red mud), was examined in laboratory studies, with results guiding the design of a greenhouse experiment using these materials mixed with P-enriched Ruston soil (fine-loamy, siliceous, semiactive, thermic Typic Paleudults) used to grow common bermudagrass (Cynodon dactylon). The Langmuir P sorption maxima of ironstone and red mud were about five-times greater than that of Ruston but sorption was affected by kinetics. Miscible displacement studies confirmed reduced P mobility in these materials compared to Ruston, and reduced mobility of P in Ruston when mixed at a 9 to 1 ratio, with red mud being more effective than ironstone. The greenhouse experiment compared Ruston mixed with the P adsorbents at 0, 5, 10 and 20% with 4 replicates in a completely randomized design. Bermudagrass yield was greatest in the red mud treatments but variability among replicates led to no significant treatment effect in mass of P leached. Decreased infiltration with red mud led to ponding lasting longer than one day, which therefore represented potential loss of desorbed soil P in runoff. However, under simulated rainfall later in the experiment losses of P were numerically least from the red mud treatments, suggesting that the shorter-term results reflected transient behavior and that red mud may have potential as a soil amendment to reduce P losses.
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Smith, Samantha Karyn, "Ironstone and Red Mud as Soil Amendments to Increase Phosphorus Retention in a Sandy Soil" (2017). LSU Master's Theses. 4488.