“We don’t have a runoff problem, we have an infiltration problem.”

That’s a quote I pulled from the bottom of an email from a conservation technician in Pierce county. What he’s pointing out is that our problem is not that too much water is getting into ditches, streams, and lakes. It’s that not enough water is being held where it’s falling. And when that water leaves the place it fell, it takes some of the soil as well as nutrients (i.e., pollutants) with it.

According to the Farmers’ Almanac, one inch of rain on one acre of land represents 27,143 gallons of water. So what happens when we get a storm that drops about 4 inches of rain on a 20 acre parcel? The impact of all that water depends on a lot of variables like how quickly the storm hits, how wet the ground already is, the type of soil on the ground, the slope of the land, and how that land is being managed.

Now there’s not a whole lot we can control about how quickly the rain falls or when it comes or many other variables. But farmers CAN do some things to control how much water their soil is able to absorb.

Pierce County conservation technician, Dan Sitz, kindly took some data from a 20 acre field southeast of River Falls which drains into the South Fork of the Kinnickinnic River and calculated how much water would leave that field during at 10-year storm¹ depending on different ways that field was managed.

As you can see from the graph, growing plants do a LOT to decrease the amount of water leaving the land. And in general, the greater the mass of plants and the longer those plants are on the soil, the more water will stay on the field.

Now you might note, this graph is measuring runoff, but that runoff is affected by land management significantly. By changing tillage practices, farmers can hold almost 20% more water in their fields according to the standard model. Research at the Horse Creek Demonstration Plot in Polk County found even more significant effects. Their trials show that farmers who don’t till and keep growing roots in the ground for more of the year see more than twice as much infiltration and half as much runoff during a 1.8 inch simulated rainstorm.

Because of the great impact management choices can have on runoff and infiltration, farmers and landowners are working to incorporate better practices onto their fields. To learn more about our peer-to-peer learning opportunities in the Kinnickinnic watershed, visit farmerledwatershed.org.

¹A 10-year storm (which is 4.24″ of rain within 24 hours for Pierce County) has a 10 percent chance of happening annually.  Larger rain events would be considered more like 25 or 100 year storm events depending on how much rain fell.

Tara Greiman is the Director of Conservation & Stewardship for the Wisconsin Farmers Union and assists local Farmer-Led Watershed Councils to enhance local farm economic and environmental sustainability. If you have questions or comments, you can reach her at tgreiman@wisconsinfarmersunion.com at 715-492-0329 or follow your local Farmer-Led Watershed Council on Facebook.com/farmerledwatershed.

Data on the Horse Creek test plot can be found at farmerledwatershed.org.