By DeAnn Presley
In our last article, we highlighted two soils from western Kansas that are excellent for crop production, Colby and Ulysses. Cropland in Kansas represents the largest land use of non-federal rural land, but not far behind is range and pastureland. As of the last USDA National Resources Inventory report in 2012, Kansas had approximately 19 million acres of range and pastureland. Although grazing lands represent such a significant portion of Kansas (36% of the land area), most of them are not suitable for crops. These soils support native grasses such as big bluestem and numerous species of native wildflowers. Native plants are uniquely suited to survive in the Great Plains and one reason is because of their roots. Did you know that more than 75% of the biomass of native prairie plants are located underground? Healthy grazing lands support more than just cattle, they are important habitats for a variety of large and small mammals, birds, reptiles, and insects.
Dwight soil series
Dwight is a common soil series in eastern Kansas, encompassing over 280,000 acres in the state (Figure 1). It formed under tallgrass prairie vegetation, and even today most of the acres are in rangeland (more on that later). It’s mapped on flat uplands in the Flint Hills, so a typical profile is a rather clayey soil with bedrock at a depth of anywhere from 3 to 5 feet below the soil surface (Figure 2).
Figure 1. Soil series extent map in Kansas for the Dwight soil series.
Figure 2. Dwight soil profile monolith.
Salty like the ocean
Dwight soils are unique because they contain high levels of salts, and in particular, they contain a lot of sodium. The word sodium comes from the English word soda and from the Medieval Latin word sodanum, which means "headache remedy." Sodium's chemical symbol “Na” comes from the Latin word for sodium carbonate, natrium. What does this have to do with Dwight? The Dwight series is a “Natrustoll” and that means it’s a mollisol (high in decomposed organic matter which is a good thing) but, when you combine lots of sodium with the clayey subsoil, the clay swells. Swelling clay reduces the soil’s permeability, and it also creates an interesting looking structure called columnar. Columnar structure looks like rectangles with round tops—as the sodium causes the clay particles to swell in three dimensions, pore spaced is squeezed out in every direction, and the tops of the rectangles puff up like biscuits (Figure 3.)
Figure 3. Columnar soil structure looks like rectangles with rounded, puffed tops
Chicken or egg? Bison or wallow?
Dwight soils occur on broad, flat uplands and if you see a little depression in a pasture in eastern Kansas (Figure 4), there’s a good chance that this is a Dwight soil. Some might look at that and call it a buffalo wallow, but a Kansan would quickly say “actually, it’s a bison wallow”. There are a lot of people that will say bison create wallows, however, might it be that that bison used pre-existing bathtubs? Created because sodium accumulated in shallow upland depressions?
For any trivia buffs out there, check out this factsheet on the American bison (scientific name Bison bison), our new national mammal - https://www.doi.gov/blog/15-facts-about-our-national-mammal-american-bison
Figure 4. Upland depression.
Wallow: To roll about in a lazy, relaxed, or ungainly manner
Oklahoma State researchers studied the wallowing behavior of bison from 1993-1995. Before they turned the bison into the pasture they counted the number of depression areas, and “observed 170 wallowing incidents” and found that bison weren’t using clayey shallow depressions (which were high in sodium) but rather, were making new wallows on less-clayey, low-sodium soils for the purpose of dust-bathing (Coppedge et al., 1999).