Radiative energy absorption of snow after liquid dairy manure application: A field-based, replicated approach

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

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2018
Publication Date: 2/1/2019
Citation: Stock, M.N., Arriaga, F.J., Vadas, P.A., Good, L.W., Karthikeyan, K.G. 2019. Radiative energy absorption of snow after liquid dairy manure application: A field-based, replicated approach. Water Resources Research. 569:51-60.

Interpretive Summary: Reducing snowmelt runoff from fields with winter-applied manure can help decrease pollution of local surface waters by manure nutrients. However, the physical processes that control snowmelt, which in turn controls runoff, are not understood well enough to develop reliable management recommendations and policies for winter manure spreading. As part of large winter runoff project, we closely monitored snowmelt dynamics by measuring radiative energy flux over two winters in Wisconsin on field plots that had liquid dairy manure applied at different winter times and different tillage management (no-till or tilled). Manure application timing (December or January, onto snow or onto bare soil) had a significant effect on radiative energy flux, while tillage had less of an effect. Overall, later winter applications of manure onto snow allowed more radiation absorbed by the snowpack and subsequent energy available to melt snow. Therefore, applications of liquid manure onto snow may increase runoff and pose a challenge for nutrient transport from the manure during thaw events.

Technical Abstract: Reducing agricultural runoff year-round is important, in particular during snowmelt events on landscapes that receive wintertime applications of manure. Previous field investigations as well as modelling tools that guide manure management, however, are less effective during the winter because of the complexity of physical processes that drive runoff and the lack of mechanistic data to build routines. Moreover, the manure matrix adds complexity, as producers have shifted from solid to liquid manures. The objective of this study was to quantify the primary driver of snowmelt, hence runoff, by measuring the radiative energy fluxes after wintertime liquid manure application. Testing these fluxes with multiple and replicated management scenarios, repeated measures, and at the plot-scale, however, resulted in a second objective to develop a practical field approach that measured albedo during winter. Six management treatments were tested in south-central Wisconsin during the winters of 2015-2016 and 2016-2017 with a complete factorial design: three manure application timings (early December, late January, and unmanured) and two tillage treatments (conventional tillage versus no-tillage). A multiple linear regression model was developed to estimate albedo with digital imagery and readily-obtained site characteristics. Manure timing had a significant effect on radiative energy fluxes and tillage was secondary. January applications of manure produced an immediate and legacy decrease in albedo, which resulted in greater net radiation absorbed by the snowpack and subsequent energy available for snowmelt. Therefore, applications of liquid manure may increase runoff and pose a challenge for nutrient transport from the manure during thaw events.