Kansas Soil of the Month for April: Pawnee
Westward, ho! The month of April was a very popular window of time for settlers to depart from Independence, Missouri and head for the Willamette Valley in Oregon. Therefore, this month we chose an important and prevalent Kansas soil that wagon trains would have traversed in April as they cut across the hills in the northeastern corner of Kansas.
Pawnee soil series
The Pawnee soil series is found extensively in southeast Nebraska and northeast Kansas, comprising over 1 million acres in total (Figure 1). About 700,000 years ago glaciers covered the northeastern corner of Kansas (Figure 2), leaving behind glacial till, the parent material for the Pawnee soil series. Glacial till is composed of all of the material that glaciers picked up as they moved towards Kansas. How do scientists know this? A clue is the pink rocks commonly found in northeastern Kansas, called Sioux Quartzite, “a pink metamorphosed sandstone more than a billion years old. Sioux Quartzite found in Kansas came from southern Minnesota, South Dakota, and northwestern Iowa” (Lyle, 2009).
Figure 1. Soil series extent map in Kansas for the Pawnee soil series. Map created using USDA-NRCS Official Soil Series Description website.
Figure 2. Geographic boundary of glaciation in Kansas. The map shows where Sioux Quartzite bedrock is found in the U.S. Any Sioux Quartzite found in Kansas today was transported from these areas in Minnesota and South Dakota by glaciers 700,000 years ago. Map from http://www.kgs.ku.edu/Publications/PIC/pic28.html.
The Pawnee soil monolith shown in the photo below was collected in Brown County, Kansas and you can see small Sioux Quartzite stones—that is how soil scientists know that they are looking at a soil formed in parent material deposited by a glacier (Figure 3, upper photo). So--the Pawnee soil contains billion-year old rocks that were transported to Kansas 700,000 years ago by glaciers.
Another iconic Kansas mollisol
Like many of our soils in Kansas, the Pawnee is a “mollisol”, meaning it contains the decomposed tissue of thousands of years’ worth of plant, animal, and microbe remains, making it a fertile soil for agriculture (note the trademark deep, dark A horizon of this mollisol; Figure 3, lower photo). Pawnee is an interesting soil in that it can often be in rangeland, cropland, or land that used to be cropland and has been returned to grassland (and then, in some cases, turned back into cropland again). The typical soil textures in the Pawnee soil profile are loam or clay loam at the surface, and clay in the subsoil, so their suitability for buildings with basements and septic system drain fields is less than ideal, but they do make “swell” ponds!
Figure 3. Pawnee soil monolith (lower panel) with a close-up view depicting Sioux Quartzite rocks deposited in Kansas by glaciers (upper panel). Photo by Kathy Gehl, K-State Research and Extension.
Pioneers left their mark on the Pawnee soil
During the Oregon Trail’s peak years in the mid-1880s, over 400,000 settlers made the journey. While many didn’t travel all the way to the Willamette Valley, it stands to reason that most traveled across the northeast corner of Kansas. Pawnee soils still bear signs of trails laid by wagons, now called swales and trail ruts. In fact, all 6 states that were part of the trail have visible swales and ruts to this day (Andrews, 2015). A faint trail, just above the blue arrow (zoom in and look closely), can be seen in a satellite photo (Figure 4) from a native grass pasture in rural Pottawatomie County (the orange lines are marking the soil types). The soil mapped at this spot is a Pawnee clay loam, 4-8% slopes.
Figure 4. Satellite photo of a pasture in Pottawatomie County, Kansas, depicting faint trail ruts on a Pawnee soil. Photo is from the USDA Web Soil Survey.
Wonder what the settlers thought of all the pink Sioux Quartzite rocks along the trail and if it ever occurred to them that the rocks were settlers too?
If you missed our first two Soil of the Month installments (Jan/Feb and March), you can find them on the Agronomy eUpdate website. Look for the last issue for February and March.
What soil will be coming in May? Stay tuned!
DeAnn Presley, Soil Management Specialist
Kathy Gehl, eUpdate editor