Dynamics of measured and simulated dissolved phosphorus in runoff from winter-applied dairy manure

Authors: Vadas, Peter; STOCK, MELANIE - Utah State University; ARRIAGA, FRANCISCO - University Of Wisconsin; GOOD, LAURA - University Of Wisconsin; KARTHIKEYAN, K. - University Of Wisconsin; ZOPP, ZACHARIAH - University Of Wisconsin

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Better information is needed on processes that control nutrient loss in runoff from fields that have manure applied in winter. We monitored nutrient loss in winter runoff from field plots in Wisconsin with and without tillage and having manure applied either in December or January. Runoff had more sediment-bound nutrients when soils were bare and unfrozen, but more dissolved nutrients when they were snow-covered or frozen. Manure solids in runoff were greatest when manure was applied on top of snow and the runoff was caused by snowmelt. Dissolved nutrients in runoff increased when manure was applied on top of snow because manure liquid remained in the snowpack and was available for loss in runoff. In addition, dissolved nutrients in runoff also increased when the proportion of rain or snowmelt included in any runoff event increased. For liquid dairy manure applied in winter, nutrients in runoff can be decreased if manure can be applied onto bare, unfrozen soil, or if the amount of runoff relative to rain and snowmelt can be reduced, perhaps through greater soil roughness from fall tillage.

Technical Abstract: Agricultural nutrient management is an issue due to nitrogen (N) and phosphorus (P) losses from fields and water quality degradation. Better information is needed on the risk of nutrient loss in runoff from dairy manure applied in winter. We monitored N and P loss in runoff during two winters from tilled and no-tillage field plots that had liquid dairy manure applied either in early December or late January. Runoff total N and P were dominated by non-dissolved forms for events when soils were bare and unfrozen. Runoff from snow-covered, frozen soils had much less sediment and sediment-related nutrients, and greater dissolved nutrients. Transport of manure solids was greatest when manure was applied on top of snow and the runoff that occurred shortly after application was caused by snowmelt. Dissolved P and NH4-N concentrations in runoff were greater when manure was applied on top of snow because manure liquid remained in the snowpack instead of infiltrating into soil, which allowed more manure nutrients to be available for loss in runoff. Dissolved P and NH4-N concentrations in runoff also increased as the amount of rain or snowmelt during an event that actually became runoff (runoff:rain+snowmelt ratio) increased. Overall, results show that for liquid dairy manure applied in winter, nutrient concentrations in runoff can be decreased if manure can be applied onto bare, unfrozen soil, or if the amount of runoff relative to rain and snowmelt can be reduced, perhaps through greater soil surface roughness from fall tillage. Both management approaches will allow more manure nutrients to infiltrate into soil and be less available to loss in runoff.