Nitrogen, phosphorus, and snowmelt runoff losses after application of dairy manure with variable solids content

Authors: Young, Eric; WILSON, MELISSA - University Of Minnesota; Sherman, Jessica; Vadas, Peter; ARRIAGA, FRANCISCO - University Of Wisconsin; Feyereisen, Gary

Submitted to: Water: A Multidiscplinary Research Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2022
Publication Date: 11/18/2022
Citation: Young, E.O., Wilson, M., Sherman, J.F., Vadas, P.A., Arriaga, F., Feyereisen, G.W. 2022. Nitrogen, phosphorus, and snowmelt runoff losses after application of dairy manure with variable solids content. Water: A Multidiscplinary Research Journal. 14(22). Article 3745. https://doi.org/10.3390/w14223745.
DOI: https://doi.org/10.3390/w14223745

Interpretive Summary: Manure is an important source of crop fertility in dairy systems, however careful management is needed to reduce the loss of nitrogen (N) and phosphorus (P) in surface runoff from farm fields where manure is applied. Runoff during the non-growing season represents a large fraction of annual runoff flows in cold climates, particularly from snowmelt events. Manure applied during the winter on top of snow may be more vulnerable to transport in snowmelt water and surface runoff compared to applying manure before snow when soils are unfrozen. More studies are needed to better quantify the range of N and P losses from winter manure application and help guide model development and best management practices. We conducted trials at three Upper Midwest sites to assess snowmelt runoff water quality after dairy manure differing in solids content (High: 12 to 15%; Medium: 7.5 to 8.0%; Low: 2.9 to 5.5%) was applied on top of snow at 26,670 L/ha. Manure drastically increased concentrations/loads of dissolved reactive P (DRP), total P (TP), total N (TN), ammonium-N, organic-N, and total solids (TS) compared to no manure controls. Snowmelt TP (0.11 to 27.8 mg/L), DRP (0.04 to 17.8 mg/L), TS (20 to 17258 mg/ L), TN (<0.1 to 115 mg/L), and ammonium-N (<0.01 to 92.2 mg/L) ranged widely. While TP, DRP, TN, ammonia N, and TS losses were generally greater for the High manure solids treatment, there was a tendency for greater DRP loss with Low and Medium treatments for some events. Snowmelt TS concentrations were strongly related with TP, TN, organic-N, and organic-P, but were not good predictors of DRP or inorganic-N concentrations. Results indicate high transport potential of manure solids, N and P with manure application on top of snow and a need for site-specific weather-based P loss indices that account for snowmelt nutrient loss processes.

Technical Abstract: Field studies quantifying snowmelt nutrient loss are needed to better predict high loss risk conditions and inform simulation models. We conducted trials at three Upper Midwest sites to assess snowmelt runoff water quality after applying dairy manure differing in solids content (High: 12 to 15%; Medium: 7.5 to 8.0%; Low: 2.9 to 5.5%) on top of snow at 26,670 L/ha. Manure drastically increased concentrations/loads of dissolved reactive P (DRP), total P (TP), total N (TN), ammonium-N, organic-N, and total solids (TS) compared to no manure controls. Snowmelt TP (0.11 to 27.8 mg/L), DRP (0.04 to 17.8 mg/L), TS (20 to 17258 mg/ L), TN (<0.1 to 115 mg/L), and ammonium-N (<0.01 to 92.2 mg/L) ranged widely. While TP, DRP, TN, ammonia N, and TS losses were generally greater for the High treatment, there was a tendency for greater DRP loss with Low and Medium treatments for some events. Mean TN and TP lost in runoff as a percentage of applied ranged from 7.9 to 64.4% and 4.5 to 33.1%, respectively. Snowmelt TS concentrations were strongly related with TP, TN, organic-N, and organic-P, but were not good predictors of DRP or inorganic-N. Results indicate high transport potential of manure solids, N and P with manure application on top of snow and a need for site-specific weather-based P loss indices that account for snowmelt nutrient loss processes.