Initial and residual benefits of soil amendments in reducing phosphorus release from soils with simulated snowmelt flooding.

In the Canadian prairies, spring snowmelt occurs rapidly and causes flooding in low-lying areas, inducing anaerobic soil conditions and exacerbating phosphorus (P) release to meltwater. Soil amendments can mitigate P loss from flooded soils soon after amendment application; however, their residual benefits are less understood. We examined the initial and residual benefits of alum (Al2(SO4)3·18H2O), gypsum (CaSO4·2H2O), and Epsom salt (MgSO4·7H2O) in a simulated snowmelt flooding experiment. Intact soil columns were taken from amended and unamended field plots in the same year and 1 year after the amendment application. The soil columns were flooded and incubated at a cold temperature. Porewater and floodwater samples were analyzed for dissolved reactive P (DRP), calcium (Ca), magnesium (Mg), iron (Fe), and manganese (Mn) concentrations, and pH. During the year of application, alum, gypsum, and Epsom salt decreased the mean porewater DRP by 68%, 29%, and 19%, and floodwater DRP by 69%, 51%, and 31%, respectively, relative to unamended treatment, with only alum showing significant differences. One year after applications, alum significantly decreased porewater DRP by 35%, but not floodwater DRP, whereas gypsum or Epsom salt did not decrease porewater or floodwater DRP. Correlation and principal component analysis revealed that porewater and floodwater DRP are positively related to pH and Fe, but only in alum-amended treatment, suggesting the influence of pH and Fe in stabilizing P. While alum was effective in mitigating P loss from flooded soils, its effectiveness decreased over time, with negligible residual benefits a year later.