Wastewater-recovered struvite effects on total extractable phosphorus compared with other phosphorus sources

Intentional precipitation of the phosphorus (P)-containing mineral struvite (MgNH₄PO₄ · 6H₂O) is an attractive option in sustainable water management due to the ability to recover P from various waste sources. Limited research has assessed struvite's potential as a fertilizer P source in agronomic soils compared with other conventional fertilizer P sources under flooded soil conditions, common for lowland rice (Oryza sativa L.). The objective of this study was to evaluate total extractable soil P over time from a wastewater-recovered struvite (ST) material in a plant-less soil incubation with two silt-loam (SiL) and a silty clay loam (SiCL) soil in a flooded soil environment compared to monoammonium phosphate (MAP) and triple superphosphate (TSP). Replicated soil cups were amended at a rate of 24.5 kg P ha^–1 and were sampled after 0.5, 1, 2, 3, and 4 mo. Total water-soluble (WS) soil P concentrations increased the most from the initial in the ST treatment (69.9 and 52.2 mg kg^–1 after 0.5 and 1 mo, respectively) than in any other treatment in the first month. However, throughout the remaining 3 mo of incubation, total WS soil P concentrations generally decreased, but remained greater than the initial, and were similar among fertilizer treatments. Averaged over time, total Mehlich-3 (M3) soil P concentrations in all three soils increased the most from the initial in the ST treatment (66.6, 71.3, and 74.5 mg kg^–1, respectively), which did not differ from MAP and TSP. The comparable total WS-P and M3-P concentrations among fertilizers under flooded soil conditions further support struvite's agronomic potential as an alternative fertilizer P source.