Srimathie Indraratne

Snowmelt runoff is a dominant pathway of phosphorus (P) losses from agricultural lands in cold climatic regions. Soil amendments effectively reduce P losses from soils by converting P to less soluble forms; however, changes in P speciation in cold climatic regions with fall‐applied amendments have not been investigated. This study evaluated P composition in soils from a manured field with fall‐amended alum (Al 2 (SO 4 ) 3 ·18H 2 O), gypsum (CaSO 4 ·2H 2 O), or Epsom salt (MgSO 4 ·7H 2 O) using three complementary methods: sequential P fractionation, scanning electron microscopy with energy‐dispersive X‐rays (SEM‐EDX) spectroscopy, and P K‐edge X‐ray absorption near‐edge structure spectroscopy (XANES). Plots were established in an annual crop field in southern Manitoba, Canada, with unamended and amended (2.5 Mg ha −1 ) treatments having four replicates in 2020 fall. Soil samples (0–10 cm) taken from each plot soon after spring snowmelt in 2021 were subjected to P fractionation. A composite soil sample for each treatment was analyzed using SEM‐EDX and XANES. Alum‐ and Epsom salt‐treated soils had significantly greater residual P fraction with a higher proportion of apatite‐like P and a correspondingly lower proportion of P sorbed to calcite (CaCO 3 ) than unamended and gypsum‐amended soils. Backscattered electron imaging of SEM‐EDX revealed that alum‐ and Epsom salt‐amended treatments had P‐enriched microsites frequently associated with aluminum (Al), iron (Fe), magnesium (Mg), and calcium (Ca), which was not observed in other treatments. Induced precipitation of apatite‐like species may have been responsible for reduced P loss to snowmelt previously reported with fall application of amendments.

Soil amendment effects on the mobility of potentially toxic elements (PTEs) have been hardly investigated under snowmelt flooding conditions. This research quantifies and compares the loadings of arsenic (As), copper (Cu), nickel (Ni), selenium (Se), vanadium (V), and zinc (Zn) to snowmelt from unamended, alum-, gypsum-, and Epsom salt-amended soils from a manured agricultural field and a non-manured agricultural field. In the fall of 2020, amendments were surface applied at a rate of 2.5 Mg ha −1 to field plots with four replicates. Runoff boxes were installed at the plots’ edge to collect winter snow. In the spring of 2021, the snowmelt in each box was pumped out, and volume was recorded until all snow in the boxes had melted. Concentrations of PTE and other cations and pH were measured in a subsample of the snowmelt. The snowmelt from the manured field had higher Ni, Se, and V loads than that from the non-manured field. There were no significant differences in snowmelt PTE loads between the amended soils and the unamended controls at each field. Although not statistically significant, the Epsom salt-amended treatment resulted in a 75% reduction in Se loading and a 44% reduction in V loading, while the gypsum-amended treatment showed a 38% reduction in Ni loading compared to the unamended treatment in the manured soil. Overall, our findings from a single season using both manured and non-manured fields suggest that alum, gypsum, and Epsom salt additions did not significantly alter the mobility of the studied PTEs during the spring snowmelt period.