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

## TL;DR

Alum reduces phosphorus loss from soils during snowmelt flooding, but its effects fade within a year.

## Contribution

This study evaluates the initial and residual effectiveness of soil amendments in reducing phosphorus release during simulated snowmelt flooding.

## Key findings

- Alum reduced porewater and floodwater phosphorus by up to 68% and 69%, respectively, in the year of application.
- Alum's effectiveness decreased over time, with only a 35% porewater phosphorus reduction one year later.
- Gypsum and Epsom salt showed negligible or no long-term benefits in reducing phosphorus loss.

## Abstract

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.

Alum amendment decreased P release from soils under simulated snowmelt flooding in the year of application.Gypsum and Epsom salt were ineffective in reducing P loss under simulated snowmelt flooding in this soil.The effectiveness of alum in mitigating P loss from soil decreased with time after amendment application.Residual benefits of amendments in reducing P loss from soils under simulated snowmelt flooding were negligible.

Alum amendment decreased P release from soils under simulated snowmelt flooding in the year of application.

Gypsum and Epsom salt were ineffective in reducing P loss under simulated snowmelt flooding in this soil.

The effectiveness of alum in mitigating P loss from soil decreased with time after amendment application.

Residual benefits of amendments in reducing P loss from soils under simulated snowmelt flooding were negligible.

Phosphorus (P) is an essential plant nutrient. Farmers supply P to crops as fertilizers and manure. However, P can be lost from croplands to water bodies such as lakes. High P concentrations in water bodies can result in algal blooms with adverse environmental effects. In the Canadian prairies, most P gets into water bodies with snowmelt runoff. Soil amendments can retain P in soil and reduce P loss from land; however, their long‐term effectiveness is unclear. We evaluated potential P loss to snowmelt from intact soil columns collected from field plots, which were either unamended or amended with alum, gypsum, or Epsom salt. Two simulated snowmelt flooding studies were conducted in the same year of the amendment application and the following year. Our results showed that alum was effective in reducing P loss from soils to snowmelt. However, its effectiveness decreased over time, with negligible benefits a year later.