The application of spent gypsum from a ditch filter did not appear to increase soil water-extractable phosphorus (WEP) or the interpretative ranking of soil test P Mehlich 3 aluminum, iron, and phosphorus (M3P), it does not appear that land application of spent gypsum would increase relative environmental risk or provide any P fertilizer value, especially at P concentrations expected to be found in the real world. It appears that P captured by gypsum filters is effectively trapped in rather insoluble forms. Therefore, the removal of P from agricultural drainage using gypsum and its subsequent land application is in effect relocating soil P from a relatively mobile soil P pool, that was subsequently lost as dissolved P in runoff or subsurface flow, to a stable soil P pool where it is unlikely to be lost, even if it is applied back to the same field. In addition, the application of spent gypsum to high P soils may further reduce P losses by removing soluble P from the soil solution. Consideration of soil type and time of application is important in determining the environmental and agronomic impacts of applying the spent materials. The results of this study indicate that when applied as a soil amendment; spent gypsum would retain its P, presenting little risk of loosing that P to surface runoff. However, it does not appear to be a viable fertilizer source except at the highest P saturation level and application rate, which would be unlikely in agronomic settings. 

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