Multi-Scale Investigation of Winter Runoff and Nutrient Loss Processes in Actively Managed Dairy AgroecosystemsK.G. Karthikeyan1, Biological Systems Engineering, University of Wisconsin-Madison L. Ward-Good, Dept. of Soil Science, University of Wisconsin-MadisonP.A. Vadas, Dairy Forage Research Center, USDA-ARS, Madison, WI W. Jokela, Dairy Forage Research Center, USDA-ARS, Madison, WIF.J. Arriaga2, Dept. of Soil Science, University of Wisconsin-Madison M. Stock, Dept. of Soil Science, University of Wisconsin-Madison

1-Project Director; 2-presenter (francisco.arriaga@wisc.edu)

Relevance: Agricultural nutrient management is an important area of research and policy development due to water quality degradation by nitrogen (N) and phosphorus (P). Manure application to fields without incorporation can be a significant source of N and P loss in runoff. Winter application of dairy manure, which is commonly practiced, is risky given frequent occurrence of runoff from snowmelt and rain-on-snow events. Many states restrict winter spreading of dairy manure, but little process-oriented research of winter runoff and manure nutrient loss has been conducted to support restrictions. Our project is investigating and improving the understanding and modeling of biochemical and physical processes controlling frozen-soil and snowmelt infiltration, runoff, and nutrient loss from soil and applied manure for actively managed dairy systems. Our objectives are to: i) conduct multi-scale experiments to investigate processes controlling winter runoff and nutrient loss from soil and manure; ii) develop novel model routines for winter manure runoff that can be incorporated into process-based, field and watershed-scale models; and iii) use runoff monitoring data to evaluate new model routines.

Impact: Our results are informing policy, guidelines, and prediction tools in northern-tier U.S. states where winter manure application is practiced. Stakeholders include policy makers and extension agents helping to develop manure application guidelines and farm practices, as well as scientists involved in measuring and modeling nutrient loss in runoff from winter-spread manure. Experimental results are novel because there has been little to no process-level research of N and P loss in runoff from winter-applied dairy manure. Results are helping to develop new prediction tools that assess N and P loss from agroecosystems and evaluate if new practices and technologies can reduce that loss. We have completed about 1.5 years of our four-year project. We have conducted two lab-scale experiments investigating nutrient release from manure to water as a function of temperature, and nutrient leaching from melting snow as a function of manure application rate and placement within a snow-pack. These results are being processed and analyzed. Last winter we conducted preliminary in-situ measurements of soil physical properties and climatic parameters to evaluate our approach for developing a water and energy budget of frozen soil. We are completing installation of the field plot-scale portion of our project that will monitor nutrient loss in runoff from winter-applied manure as function of tillage and manure application timing treatments. The field project will be monitored for three years, beginning in winter 2105-2016.

Overall Goal and Objectives: The overall goal of our proposed project is to investigate and improve the understanding and modeling of biochemical and physical processes controlling frozen-soil and snowmelt infiltration, runoff, and nutrient losses from soil and applied manure for actively managed dairy systems. Our specific, supporting objectives are to:1. Conduct multi-scale experiments to investigate biochemical and physical processes controlling snowmelt,

snowmelt infiltration and runoff, and nutrient loss from soil and manure.2. Develop model routines for winter manure runoff processes from Objective 1 that can be incorporated into

process-based, field- and watershed- scale models.3. Use available runoff monitoring data to evaluate the new model routines.

Field Scale Study Approach and Preliminary Results: The field study is located in southcentral Wisconsin, near Arlington. At this scale, we are focusing on measuring winter and early spring runoff events. Soil and weather variables are been assessed to estimate water and energy balance budgets (Figure 2). This information will be used for model subroutines that estimate the time and magnitude of runoff events, which can then be coupled with multi-scale nutrient loss data to aid in estimating nutrient losses.

Figure 1. (A) Treatments include tillage (chisel/disk and no-tillage) to study the impact of soil surface roughness, and manure application timing [no manure, early winter (no snow cover), and late winter (on top of snow)] in a complete factorial arrangement replicated three times. (B) Each plot is 4.5 m wide by 15.2 m long with a trench dug around their periphery to prevent runoff water from entering/leaving the individual plot area, and a collection flume towards the bottom to collect runoff. Runoff is diverted to a box containing three collection buckets per plot. The first bucket collects all the runoff and when filled it diverts 1/24 of the runoff volume to the 2nd bucket using a weir crown head. Similarly, the 2nd bucket has a weir head to divert 1/24 of its receiving water volume to the 3rd bucket. This system can collect a total runoff volume of 163 mm (6.4-inches) per event.

Figure 2. Schematic of the soil and atmospheric variables been measured. (A) The water budget of the these systems is estimated via several measurements of soil variables, such as liquid water content, matric potential, depth of frost, soil temperature, precipitation, among others. (B) Atmospheric parameters are measured to determine the energy budget and help establish conditions conducent to snowmelt and increased runoff potential.

(A)

(B)

(A) (B)

Figure 3. Visual field conditions of the plots and weather station area in chronological sequence during late winter 2014-2015. In general, there was little snowmelt induced runoff in Wisconsin this past winter.

Figure 4. The lowest air temperature (A) recorded was -25.6°C. Snow (B) acts as an insulator and limits ground heat fluxes (C), which can prevent frozen ground from thawing (D). Ground heat flux increased in early March, leading to fast thawing of the frozen soil. A brief cold period towards the end of March shows how fast soil can freeze. Soil temperature matched frost tube data closely (D). Data were unavailable early in the winter season due to technical issues.

(A)

(B)

(C)

(D)

potential sensor issue

soil thawing

Figure 5. The liquid water content of the soil (B) decreased as soil temperatures decreased (A) and soil water froze. Similarly, the soil matric potential increased during soil frozen periods (C). The dynamics of a downward soil freezing front can create an upward water flux due to the increasing matric potential as liquid water changes phases to a solid. These type of phenomena can affect nutrient distribution in the soil profile and losses in runoff.

(A)

(B)

(C)

Figure 6. Runoff collection buckets were equipped with load-cells to measure runoff as it occurs. This type of information will help determine soil and weather conditions triggering runoff events.

We would like to acknowledge Melanie Stock, Research Assistant, for her tireless efforts on this project.