Minnesota is the land of rolling prairies, the hills and valleys of the karst topography and the relatively flat lands of the valley in the North West region of the state. I learned to call all lands relatively flat instead of flat when I lived in an area of the U.S. not unlike the valley, and I was told to meet someone on “that ridge over yonder.” The ridge was a rise in the landscape of no more than 12 inches in a quarter of a mile distance, but to them it was a ridge.
When we talk about water erosion, there is some common terminology for what we are talking about. Sheet erosion is defined as the movement of thin layers of soil by surface flow across a field. Because sheet erosion doesn’t leave any “tracks” across a field, we only notice it by slight fine soil deposits at the bottom of long gentle sloped land and frequently don’t pay it too much attention. More obvious is rill erosion lines in a field. These are washes in a field that are less than 12 inches deep and for the most part can be or are removed by tillage practices. In the high volume rain events such as we have experienced recently across the state, the presence of gully erosion can also be found in some fields where the rill has deepened beyond 12 inches and in the process of water moving out of the field, some bank sloughing has also begun cutting a wider path. Gully erosion is also defined loosely as soil displacement that is difficult to remove with tillage alone.
Science published an article in 2000 (Easterling et al. 2000. Climate Extremes: Observations, modeling, impacts. Science 289:2068-2074) showing increases in extreme rainfall events (defined as 1 day event totaling greater than 4 inches) in the United States since 1910 to date. These increases were greatest in regions including the Midwest and Great Lakes region. Other U.S. government sites also post similar predictions using modeling based on these measured trends (http://www.climate.gov/news-features/featured-images/heavy-downpours-more-intense-frequent-warmer-world; http://www.epa.gov/climate/climatechange/science/indicators/weather-climate/index.html).
Whether you agree with predictions of climate change or not, the data does show more frequent intense high rain events in the upper Midwest. If this pattern continues, we should take another look at how we manage erodible land.
If you notice increased sheet, rill or gully erosion in your fields after rain events this year compared to the past, consider the erosion control methods you have employed may not be strong enough protection on the land you manage in the future. Adding or strengthening existing grassed waterways, adding sedimentation structures to slow the water movement and reduce erosion loss, terracing and tilling/planting on the contour or other water slowing practices may help you retain more of the soil resource on your individual farms.
After listening to MSGA director Larry Muff talk about his practice and strategy on his farm this week during the USB Confluence Project Tour stop, we also need to manage each field by the slope, soil type(s), and crop history independently. While this requires more planning and management, your ultimate goal is to retain your greatest physical asset, your land. This year has shown, across many fields, that this resource can be quickly lost despite conservation practices that have worked for more than a generation. Take another look in the field, evaluate any soil loss you may find, strategize if more can be done to retain your soil on an individual field basis and base your actions on the best information you can find.