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November 2017 • PDPW • Dairy’s Bottom Line
Control weather effects Amber and Tim Radatz
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t’s no secret there are elements of farming that can’t be controlled – the weather and markets to name a couple. The team at the University of Wisconsin-Discovery Farms often receives weather-related questions. They monitor water Amber quality at edgeRadatz of-farm fields including surface runoff and rain measurements. As technologies and data Tim Radatz -recording systems improve, weather is indeed becoming more predictable – or more forecastable at least. And while weather can’t be controlled, its effects certainly can be mitigated. As programs of UW-Extension, the Wisconsin and Minnesota Discovery Farm teams have monitored 127 site-years worth of edge-of-field surface runoff. During that time frame, 2,184 surface-runoff events were measured. A mere 10 percent of them represent the
Table: Nitrogen, Phosphorus and sediment loss by rainfall-return period
majority of the nutrient and soil losses that occurred. As part of the UW-Discovery Farms research, all surface runoff events were paired with rainfall data. Rainfall-intensity data was then compared with data from the National Oceanic and Atmospheric Administration for each location, to define rainfall-return periods for each runoff event. A rainfall-return period is an estimate of the likelihood of a rainfall event to occur. For example, a rainfall event with a 100-year return period would be expected to occur once in every 100 years. In any given year the probability of a 100year rainfall event occurring is one in 100 or 1 percent. In general, as the return period increases, so does the rainfall intensity. While the dataset includes several large storm events, most
runoff events – and phosphorus and nitrogen losses – are generated by storms with a rainfall-return period of less than one year, as shown in the table. Our conservation practices are often designed for 25-year storms. Even though technology is advancing rapidly, traditional conservation practices are still the backbone to preventing soil and nutrient losses during storms. Waterways, contour farming, limited soil disturbance and grade-stabilization structures are examples of the traditional soil-conservation practices that work to improve a farm’s environmental resiliency, no matter the size of the storm. During one UW-Discovery Farms project on a farm in the Driftless Area region of Wisconsin, a grade-stabilization structure was installed – specifically a check dam. As a result
the average sediment concentrations deposited in grassed waterways nearby were reduced by 73 percent. A check dam is a small dam constructed to reduce the velocity of water flow in order to counteract erosion, but many other structures can serve similar purposes. Refer to “Conservation Benefits of a Grade Stabilization Structure,” by UW-Discovery Farms and Kyle Minks, a Dane County land and water-resource scientist. The time window during which soil is frozen and snow is melting is an important period for runoff in Wisconsin, Minnesota and the rest of the Upper Midwest. In fact, this is typically when more than half of surface runoff occurs. The period is also important for phosphorus and nitrogen movement even though soil movement is limited during snowmelt.
Illustration: Surface runoff; soil, phosphorus and nitrogen loss by non-frozen and frozen soil types