New eUpdate monthly series for 2018: "Kansas Soil of the Month"
Did you know that according to Jeff Hellerich, State Soil Scientist with the NRCS, there are more than 430 different soil series (species if you will) in Kansas? The soils that make up Kansas, a “breadbasket” state, are some of the most fertile soils in the world. In fact, many consider soil as Kansas’ most valuable natural resource. The rich soil is the medium for our state’s incredible capacity to grow crops and provide grazing land. The rate of soil formation is so slow as to consider soil a non-renewable resource in terms of our life span. An appreciation and understanding of our soils is the aim of this new eUpdate series, “Kansas Soil of the Month”. Inspiration for this series didn’t strike until recently, therefore the kickoff article will feature two soils, one each for January and February.
January and February Soils of the Month: Colby and Ulysses – Sister soils of western Kansas
Each soil in Kansas is unique and distinctive from one another in different ways. Soils are classified into several different categories and the narrowest one is called the ‘soil series’ or name. No two soils have the same soil series name. How do soils get their names? Soil series are usually named after a geographic place near where they occur, like a town or landmark.
Since we are highlighting two soils for this issue, let’s compare and contrast their similarities and differences:
How are these soils similar to each other?
Colby and Ulysses are two very common soil series in western Kansas, encompassing over 5 million acres between them (Figure 1). These soils have a lot of similarities. They both formed under short-grass prairie vegetation. Today they are excellent for producing crops and are commonly irrigated, as these soils occur in the part of western Kansas that receives 18 inches or less annual precipitation. These soils might be flatter than a pancake, as they have slopes of only 0.5 to 1%.
Figure 1. Soil series extent map in Kansas for Colby (red) and Ulysses (green). Map created using USDA-NRCS Official Soil Series Description website.
Windblown silty deposits, called “loess”, is the parent material of the soil. The word “loess” is of Swiss-German origin and means “loose.” The commonly accepted way to pronounce this in the U.S. is “luss,” rhyming with fuss or muss. As the word implies, loess-derived soils are not dense, but instead are very porous. Loess soils are high in silt, and silty soils are excellent for growing crops because silt can hold a lot of water at a tension that plants can use. Soils high in clay hold a lot of water but at a tension that plant roots have trouble using. Sandy soils drain and dry out quickly, but silty soils drain well and plant roots can take up the water easily.
Another important feature these two soil series have in common is the presence of calcium carbonate, or lime, which is common in dry parts of the world. Sometimes when these loess-derived soils in Kansas erode, they can result in high-pH soils very near the soil surface, which can cause problems with the availability of certain plant nutrients. Many plant nutrients are most available around a pH of 6.5, which is slightly acidic. However, the pH of the Colby or Ulysses soils can easily be about pH 8. Phosphorus and iron are the plant nutrients most affected by high-pH soils, as these elements are less available for plant uptake at a high soil pH.
Funny thing about loose, wind-deposited sediments: They erode. Silt particles are not at sticky as clay particles, so they can easily detach and become airborne. Silty soils are very erodible when left exposed to the wind or rain. It’s very important to keep these soils protected during the windiest months, which are November through April in Kansas. Conservation practices and structures are very necessary, including windbreaks and practices that maximize residue coverage. For more information on controlling wind erosion, see the KSRE publication “Principles of Wind Erosion and its control” at https://www.bookstore.ksre.ksu.edu/pubs/MF2860.pdf.
How are these soils different from each other?
One thing that really sets the Colby and Ulysses soils apart from each other is the organic matter content in the topsoil. The Ulysses series has about 9 inches of dark, organic matter rich soil on the surface, while the Colby series is a lighter brown color at the surface (Figure 2). Therefore, the Ulysses series classifies as a “Mollisol”, while the Colby soil is an “Entisol.” Just like you can classify plants, animals, etc., you can classify soils. The word “mollisol” comes from the Latin word “mollis” for soft, because it is rich in humus, which is decomposed organic materials from plants and microbes. For an Entisol, think “infant” and you’ll be close—the Colby soil only has A and C horizons, so it is a young soil with no development other than formation of the A horizon.
Figure 2. Side by side comparison of Colby and Ulysses soil monoliths. The Ulysses profile has a distinctively darker surface horizon that extends deeper in the profile compared to the Colby series. Photo by DeAnn Presley, K-State Research and Extension.
DeAnn Presley, Soil Management Specialist