Iowa erosion rates are greater than we think

In the Iowa Learning Farms April webinar, held yesterday, Iowa State University Agronomist Rick Cruse painted a dirty picture. He said that sediment runoff rates in Iowa are much higher than official reports state.

erosion_bettsEphemeral gullies–those channels that are created in fields after a rainfall–carry a large amount of sediment away from the fields. These gullies are not accounted for in official erosion reports from the NRCS and the Iowa Daily Erosion Project.

Farmers are losing precious topsoil, especially when the gullies are graded over and filled again. Water will recreate these channels at the next rain, carrying the soil with it that was replaced earlier.  Cruse says “this is an incredibly efficient way of removing soil from the field.”

People seem to be complacent when we talk about soil erosion in Iowa. The national standard Tolerable Rate of soil loss (T) is an average of 5 tons per acre per year. The key word here is “average.” When erosion rates are averaged, Iowa is within the 5 T standard. But what about those fields where the loss is much greater than the tolerable rate?

Iowa_Soil_erosion_mapThe Iowa map is a “snapshot” of the erosion rates per township for one day. The map is taken from the Iowa Daily Erosion Project website. Note the townships shaded in colors other than green–these are areas where soil erosion rates were 5 tons and greater. And this map is not accounting for the ephemeral gullies and small channels that are whisking away that topsoil with every rainfall event.

Cruse’s presentation was highly informative and there was a lot of discussion with those who logged on. I wasn’t sure, but I thought I heard a collective “gulp” from those who were watching.

You can watch the archived session to hear Rick’s message:
http://www.extension.iastate.edu/ilf/page/webinars.

You can watch all of the ILF webinars here, too. There is a great variety of topics to choose from.

-Carol Brown

 

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