Soil Forming Factors of Brown County
As we wind down 2018, we wanted to ease back on some of the data intensive topics we’ve been hitting pretty regularly. For the next couple weeks, we will be focusing less on the data centric themes and take some time for some hopefully informative, yet easy reading topics.
This week, I thought I would hit on the soil forming factors of Brown County. Now before you hit the back button, this is going to be a short one—and remember, your day to day farming operations depend on this soil beneath your feet. So, take a minute and read along about where this soil came from and how that affects us.
To start off, the following factors are the five soil forming factors that create soils.
1. Parent material
3. Living organisms
Today, I will mainly focus on the parent material. This will largely explain how the soil we have got here. Then I will briefly talk about the other factors and how they have changed and weathered the soil in place.
Parent materials in western and central Kansas were largely derived from the uplifting of the Rocky Mountains, some 40-70 million years ago. As the mountains were pushed up, the overlying sediment was deposited across Kansas by streams and flood events. In the eastern part of the state much of the top soil is wind blown loess, carried from the states to the east of us as well as silt deposits from glacial drift to the north and east of Kansas.
The very northeast corner of the state where we are sitting was actually part of a glaciated zone. This part of the state had two glaciers deposit sediment and rocks. The first glacier was somewhere between 2.6 million and 600,000 years ago and only reached the very northeast corner. The second glacier was around 600,000 years ago and extended farther into Kansas, as far as Topeka and Lawrence. As a glacier moves forward, it grinds rocks down into silt and pushes material forward. In Kansas, it is likely that the glacier was not at its maximum extent for a very long time, and consequently, we don’t see large moraine deposits where the terminal end of the glacier sat for a long time. It is also surmised that the climate in Kansas at the time was not very conducive for maintaining glaciers. This is why the glacier only extended as far as it did into Kansas. The origin of the glacier kept pushing it in to Kansas, where the terminal end kept melting and the water washed away the deposited material. We see minimal evidence of glaciation around this part of the state now due to high amounts of weathering. Some deposited material can be seen as rocks and boulders. In northeast Kansas, we see higher amounts of rose quartz that were derived from South Dakota and Minnesota and then deposited by glaciers. We also see a very large about of material deposited from glaciers as silty materials that were the source for the next deposited layer: loess.
Finally, over the top of the glaciated material is often a layer of loess deposits. This is called the Nebraska and Kansas Loess-Drift Hills. These were largely developed under grassland vegetation. A very small section of land along the Missouri river is part of the Iowa and Missouri Deep Loess Hills. These underwent development under grasslands and forest vegetation. This loess was derived from the silty particles left behind from glacial outwash. High winds carried this ground up rock, or silt all across the Midwest. The Kansas Geological survey notes the impressive deposition of loess in the part of the state.
“Thick deposits of loess, more than a hundred feet thick in places, occur along the bluffs of the Missouri River. The loess in this region is typically a yellowish-buff, porous silt that crops out with steep faces along hillsides and valley walls. Small, white shells of snails also may be found in the loess. In northeastern Kansas a very rich soil has developed on the loess, especially in Brown and Doniphan counties and along the bluffs of the Missouri River as far south as Kansas City. Loess hills in Doniphan County are some of the highest in the state. One of these, Lookout Mountain north of Sparks, is more than 350 feet above the floodplain of the Missouri River.” (http://geokansas.ku.edu/rocks-and-minerals-of-glaciated-region)
This difference in sequence of soil deposits also affects the elevation across the state. The combination of uplift and deposits from the Rocky Mountains, as well as loess deposits across the state results in a higher elevation in the western part of the state, and a gradual decrease in elevation as we move to the southeast. Figure 1 shows a typical cross section of our loess derived soil series in the northeast part of the state.
Our climate has also largely contributed to the suitability of our soils. Higher rainfall amounts mean a moderate amount of weathering that breaks down residue and helps with formation of organic matter. Our topography is such that the majority of the water sources in the county come from groundwater. Horton is the only location in the county that uses surface water for its main water supply.
Our soils = our great success
The glacially derived soils in our part of the state resulted in a very deep soil strata in which to optimally grow crops. A 1960 book on the Soil Survey of Brown County Kansas outlined the high productivity of the soils and estimated average yields for the different soil series across the county. Estimates ranged from 36 bushels per acre corn yields on a steeper Burchard clay loam, to 85 bushels per acre on a Muir Silt Loam, both under what was termed “improved management”. Similarly, soybean yield from 18 bushels per acre on a Pawnee clay loam, and 32 bushels per acre on a Wabash silty clay were expected. It is impressive to see what we are producing today on those same soils, nearly 60 years later.