Why Study Risk and Runoff Potential?
Identifying time periods when land application of manure is likely to contribute to surface runoff contamination is important for making proper management decisions and reducing the risk of surface water contamination. Recently, a great deal of attention has been focused on reducing nutrient and sediment losses from the winter period. However, sediment and nutrient losses during the late spring period can be significant and it is important to understand landscape and weather conditions that lead to elevated runoff risk during this time period.
What Did We Do?
Surface runoff and weather data were gathered at multiple edge-of-field Discovery Farm monitoring stations in Wisconsin. Soil moisture data were also collected. Data were analyzed by each storm event during the non-frozen ground period to determine the impact of antecedent soil moisture on surface runoff generation.
What Have We Learned?
Data from the Wisconsin Discovery Farms Program has identified two key time periods with an elevated risk of surface runoff from agricultural fields: the late winter period (February – March) and the late spring period (May – June). Eighty-one percent of the average annual surface runoff was observed during these two time periods with the late winter period accounting for 50% and the late spring period accounting for 31%. Data collected over the past 12 years of the Wisconsin Discovery Farm Program indicate that the vast majority (86%) of non-frozen ground runoff occurs when soil moisture is in excess of 35%. High antecedent soil moisture can indicate risk for surface runoff in agricultural watersheds and can also influence the quantity of surface runoff generated during rainfall events. Avoiding manure applications during time periods with a high probability of rainfall and when soil moisture is at or near threshold levels decreases the risk of surface water contamination. Agricultural producers can utilize soil moisture measurement to guide the timing and rate of manure application to further reduce environmental risk.
Producer education and outreach
Tim Radatz, Research Specialist , Discovery Farms MN & WI, firstname.lastname@example.org
Anita Thompson, Associate Professor, University of Wisconsin – Madison
Fred Madison, Professor, University of Wisconsin – Madison
Radatz, T. F., Thompson, A. M. and Madison, F. W. (2012), Soil moisture and rainfall intensity thresholds for runoff generation in southwestern Wisconsin agricultural watersheds. Hydrol. Process.. doi: 10.1002/hyp.9460
UW Discovery Farms Program and Staff
UW-Platteville Pioneer Farm Program and Staff
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