Comparison of manure application methods on nutrient and metal loss to snowmelt

Abstract

Manure injection is well documented to reduce rain-driven nutrient losses, but the effect on snowmelt-driven losses is less studied. This study examined the surface application versus injection of liquid swine manure on phosphorus (P), nitrate‑nitrogen (nitrate-N), zinc (Zn), manganese (Mn), iron (Fe), magnesium (Mg), and calcium (Ca) release from soils to snowmelt. Manure was applied in the fall of 2021 to four replicated plots of surface-applied or injected treatments, and boxes were installed to collect snowmelt in each plot, including four unmanured (control) plots. In the spring of 2022, the snowmelt was collected from each box for 10 days, volume was recorded, and analyzed for dissolved reactive P (DRP), nitrate-N, Zn, Mn, Fe, Mg, and Ca concentrations, and pH. The mean daily snowmelt volume and snowmelt depth ranged from 2.9 to 25.2 L, and 2.7 to 23.3 mm, respectively. The mean snowmelt DRP concentrations for manure injected, surface-applied, and control treatments were 0.66 ± 0.07, 0.89 ± 0.07, and 0.65 ± 0.07 mg L−1, respectively. The mean DRP concentration did not vary among the manure application methods for the first 5 days of snowmelt. However, DRP was significantly higher in the manure surface-applied treatment, compared to both control and manure-injected treatments on days 7 and 8, compared to the control on day 6, and compared to the manure-injected on day 9. The effect of the manure application method on nitrate-N (3.27 to 3.60 mg L−1) and metal concentrations in the snowmelt was not significant. The cumulative loads (mean across application methods and sampling days in kg ha−1) of DRP (0.56), nitrate-N (4.03), and metals [Zn (0.11), Mn (0.01), Fe (0.18), Mg (8.03), Ca (21.70)] mobilized with snowmelt flooding did not significantly vary among the manure application methods. Results suggest that DRP, nitrate, and metal loads were primarily controlled by the snowmelt volume rather than their concentrations. Therefore, land management practices that reduce the volume of snowmelt discharge could be more effective for reducing the P, nitrate-N, and metal loss to snowmelt from manured soils.