CHAPTER 9
The fertility and productiveness of the country I had passed through gave me the highest idea of its capacity for maintaining a great agricultural production. It seemed to me as if I had never been in a country where agriculture could be practiced with less expense, or greater success.—Featherstonhaugh 1847
Often the share would go the entire “round” without striking a root or a pebble as big as a walnut, the steel running steadily with a crisp crunching ripping sound which I rather liked to hear.—Garland 1917
“[P]rairie soils,” a secondary product rather than cause of grassed surfaces.—Sauer 1950
In fact, the role of vegetation in soil genesis is of such far-reaching effect that it is generally conceded that without vegetation there could be no soil.—Weaver 1954
The moles, skunks, and badgers also move large amounts of soil in their activities and contribute greatly to the internal instability of the prairie.—Curtis 1959
Out of the raw, lifeless stuff brought by glaciers and winds, rich soils were slowly formed in a complex melding of organic and inorganic agents that was monitored by the master hand of climate.—Madson 1982
ONE OF THE MOST interesting experiences for a prairie lover is visiting a restored prairie adjacent to a native prairie. Start in the restored prairie and walk into the native. You’ll notice a difference after the first or second step into the native prairie. The soil under the restored prairie, even if the restoration is several years or decades old, is hard. The soil under the native prairie is springy. Cornfield soil is “heavy and solid” while the native sod is “soft, almost fluffy” (Madson 1982).
The prairie soils are why almost all the prairie is gone. They are arguably the most fertile and productive soils on the planet. This fertility was recognized by the early explorers, who wrote “no better soil could be found” (Jolliet 1673), “the soils, which yield bountifully” (DeGannes 1695), and “the fertility and productiveness of the country” (Featherstonhaugh 1847). Oddly, the first settlers seemed to ignore or be ignorant of that fertility “because they did not trust the grasslands” (Archer and Bunch 1953).
These were a forest people; they had a tradition that you had to clear the trees away before you could farm. . . . They were afraid of the prairies; they looked empty and lonesome. (Peattie 1938)
The prairies were generally a trackless waste, any man who bought and improved land out in mid-prairie, at that day, was laughed at for his folly. (Faragher 1986)
Indeed, this mistrust of the prairies and prairie soils largely shaped early settlement patterns across the tallgrass region as people continued to farm the forested areas along the edges of the prairie.
So the early arrivals settled at the edge of the timber, or in a woodland “grove.” It was nearly ten years before the first hardy souls ventured out on the prairie to live. By that time the “groves” and “points” (where the trees extended into the prairie along minor streams) were all occupied. Newer arrivals were forced to spread out and so, unknowingly, to get the best lands. (McFarland 1969)
In addition to prairie being unfamiliar to those coming from forested areas, the prairie was lacking one basic ingredient of pioneer life, wood. Houses were built of wood and heated with wood. Food was cooked with wood. Most tools were made of wood. The prairie-forest margin was the best of both worlds for many, wood for all the necessities and pasture for the livestock (Van Tramp 1868; Shimek 1911).
Breaking the prairie nearly broke many early farmers. Their horses and oxen probably fared even worse (Farnham 1846; Madson 1982), even when “five to ten yoke of oxen” pulled the plow (Faragher 1986) or “four horses strained desperately in their traces” (Garland 1917). Those roots had been in the soil for millennia and they did not give up easily.
In fact, it wasn’t until John Deere invented the moldboard plow in the 1830s that they could break the prairie at all. The steel blade on the moldboard plow was self-scouring. Before that, with wooden or iron blades, the farmers had to stop frequently to scrape the soil from the plow’s surface. Few of the plant roots were easy to break through and they collectively gave a new meaning to the term Gordian knot.
The tough wirelike roots of the bluestems and prairie clovers twanged with a thousand ringing sounds as each step of the horses pulled the sharp blade forward through the sod of ten thousand years. (Costello 1969)
As the furrow was cut, there was a constant popping sound, like a volley of tiny pistol shot, caused by the breaking of the tough roots and spurs. This incessant cracking and popping had a slight ring to it, amplified by the tempered steel of the moldboard plow. (Madson 1979)
One of today’s most popular prairie plants was decidedly unpopular with those breaking the prairie. The roots of leadplant, known to settlers as prairie shoestring, broke with a “characteristic snap” (Weaver 1954) and “briefly held up the plow before they popped” (Reichman 1987). However, in the end, the prairie was no match for that much steel and muscle.
At last the wide “quarter section” lay upturned, black to the sun and the garden that had bloomed and fruited for millions of years, waiting for man, lay torn and ravaged. (Garland 1917)
It wasn’t just the vast fields soon to be planted to corn and wheat that caused problems. Even a vegetable garden tested the strength of many. If the prairie roots and sod tested twenty oxen, we can only imagination the frustration of those who wielded only a hoe.
After selecting a garden spot in front of the cabin, on the verge of the prairie, she began to chop at the sod, only to have her garden hoe rebound as if she struck solid rock. The sod was impervious to horticultural tools. (Faragher 1986)
None of us today has seen an endless tallgrass prairie, or walked miles back and forth behind a yoke of oxen. We can assume that each evening they felt a sense of accomplishment. As the breaking continued, some began to regret what they were losing.
I confess that as I saw the tender plants and singing flowers bow beneath the remorseless beam, civilization seemed like a sad business and yet there was something epic, something large-gestured and splendid in this “breaking” season. (Garland 1917)
The turned turf lay smooth to the light, and the ancient roots began their rot and deep ferment. This way they broke the prairie’s heart, an acre a day at the best. (Peattie 1938)
At the same time, people were beginning to see the problem that would plague the Midwest ever since, erosion.
One day, just as the early sown wheat was beginning to throw a tinge of green over the brown earth, a tremendous wind arose from the southwest and blew with such devastating fury that the soil, caught up from the field, formed a cloud, hundreds of feet high, a cloud which darkened the sky, sending noon into dusk, and sending us all to shelter. (Garland 1917)
Many of the conservation efforts across the midcontinental grasslands over the twentieth century were focused on soil erosion. Prairie soils have a date, perhaps an arbitrary one, which we can associate with them: March 21, 1935.
On that day a black mass of blowing dirt moved across Washington, DC, blotting out the midday sun. Conveniently, and well planned out in advance, Hugh Bennett was testifying in Room 333 of the Senate Office Building on the need for more and better soil conservation practices. He procrastinated, delayed, and read reports to drag out the time. Eventually one of the Senators stated, “It is getting dark. Perhaps a rainstorm is brewing.” Then Bennett began his testimony (Brink 1951).
Erosion had long marked and left its name on the midwestern landscape. Minnesota, known for its ten thousand crystal clear lakes, is actually named after a sediment-filled river (Keating 1823; Nicollet 1838). The prairie region has two Red Rivers, one on the boundary between North Dakota and northern Minnesota, and one between Oklahoma and Texas. The name Red River implies that they were rarely crystal clear. The Platte River was too thick to drink and too thin to plow, while the Mississippi River has always been famously muddy.
Lewis and Clark’s journals also show numerous references to siltation or sedimentation. As the Corps of Discovery started to move up the Missouri River, they made comments about muddy water or the riverbanks falling into the water on May 15th, May 24th, May 29th, June 1st, June 10th, June 14th, and June 15th. And that was just the first month of the expedition.
Prairie soils are actually a product of erosion. The parent material for the Midwest’s soils came from farther north, dragged down by the glaciers. Other material came from the west, washed down from the Rocky Mountains or blown in on the winds. These wind-blown soils were called loess, with the most well-known deposits being the Loess Hills of western Iowa. In some places, glacial deposits were over six hundred feet thick (Mutel 2008). Although locked in place by roots after the prairie established, in the late Pleistocene, some of the dust storms may have rivaled or been larger than the human-caused dust storms of the 1930s (Seastedt 1995).
Geology, glaciers, wind, and rivers create dirt. Biology, plants, animals, fungi, and microbes create soil.
We may not say that the soil of the prairie patches, which is unlike all other soils of the region, is responsible for the development of the prairie, but rather, the long occupancy by grassland has resulted in the development of this particular soil. (Braun 1928a)
Prairie grass communities preceded the prairyerths, but prairyerths once established favor the continuation of prairie. (Transeau 1935)
Virtually every terrestrial form of plant and animal, from microbe to mammal, has an impact on soil formation. (Reichman 1987)
Before we continue, our story of America’s tallgrass prairie must take a brief detour to Europe in the 1640s. There a chemist named Johannes Baptista Van Helmont started the research that eventually informed us about how plants grow. In his day, people thought that plants grew aboveground by absorbing or removing material from belowground.
Van Helmont placed a willow shoot weighing five pounds into two hundred pounds of dried soil. He watered the willow and watched it grow for five years. He then carefully dug up the willow and found it weighed 169 pounds. He dried and weighed the soil and found the soil weight had only decreased by two ounces.
What Van Helmont had inadvertently discovered was photosynthesis, the capture of light by plants and the conversion of light energy into plant biomass through the process of carbon capture. Some of the carbon captured from the air in photosynthesis ends up as or in the roots. Those roots eventually die and become soil. The carbon that makes the soil black comes from the clear air and bright sunlight.
The grassland vegetation has exerted a powerful influence as a soil-builder. Plants, which introduce the living, biological factor into soil formation, return much more to the soil than they take from it. (Weaver 1968)
Belowground, the roots compete for water and nutrients in the dark as much as the leaves compete for sunlight aboveground. This is why there are so many roots at so many different depths within the soil. One of the easiest places to see this competition is in restorations. In the initial phases of the prairie restoration, managers usually try to kill off as many of the existing plants as possible. This means there’s very little competition. Whatever species gets there first and gets established can quickly crowd out others. This often happens when too much grass seed is used relative to forb seed in the initial seeding, but sometimes forbs can use this to their advantage also.
Thus, when the reputedly very conservative rattlesnake master (Eryngium yuccifolium) was introduced in a few places in the University of Wisconsin Arboretum, it literally exploded, making a solid stand several acres in extent, almost to the exclusion of all other plants. The blazing stars, yellow coneflowers, and prairie docks have done the same. (Curtis 1959)
Burrowing through all that soil to get to deeper water takes a lot of effort and energy on the plant’s part. That points to one of the differences between roots, belowground, and shoots, aboveground. When shoots grow, they move upward into air. When roots grow, they move down into rough, abrasive soil. However, soils are generally moist, and temperatures don’t change much. Shoots aboveground have to deal with blazing hot afternoons, drying winds, and thunderstorms. Aboveground is a very dynamic environment, while belowground is relatively stable.
Prairies are famous for their deep roots. Prairie rose can send roots twenty feet into the soil, while dotted blazing star can send roots sixteen feet down. The primary root of compass plant can go down almost fourteen feet (Sperry 1935; Weaver 1954).
However, not all plants sink all their roots this deep; 43 percent of roots of big bluestem are in the top four inches of soil and 78 percent of the roots are in the top twelve inches. When it rains, these roots are able to absorb a large percentage of the water that soaks into the soil (Weaver 1968). Similar studies found that 59 percent of prairie roots were in the top two inches and 87 percent were in the top ten inches (Dahlman and Kucera 1965).
Roots are important to prairie plants and plants make a large early investment in their roots. After a summer’s growth, button blazingstar was three inches tall but three feet deep (Weaver 1954). In the first seventy days, big bluestem roots grow 21 inches into the soil. Cumulatively, all those roots add up. After three years, there were 5.5 tons of roots per acre in a big bluestem planting (Weaver 1968).
In my own restoration efforts, I started some prairie turnip seed in peat pots. I pulled one seedling from the soil approximately six hours after it broke the soil surface. The shoot was about a quarter inch above the soil while the root had already grown almost six inches below the surface.
Some plants are able to live, directly or indirectly, off the efforts of other plants. This can have some interesting effects on plant diversity and abundance. Lousewort or wood-betony is a hemiparasite of prairie plants. Hemiparasite roots graft onto other roots and steal water, minerals, or carbon molecules while still conducting their own photosynthesis. The best plants to parasitize are the common and dominant species such as big bluestem.
Lousewort can influence the entire plant community by reducing the dominance of some grasses. Plant diversity correlates to the amount of lousewort in the prairie (Hedberg et al. 2005). In Wisconsin, lousewort reduced the flowering of the dominant grasses by 90 percent and leaf height by 50 percent. Seven years after researchers introduced lousewort, seventeen species of forbs bloomed in the area where lousewort was established and the dominant grasses were reduced (R. A. Henderson 2003). False toadflax, northern bedstraw, and pussy-toes are species that are either hemiparasitic or allelopathic. Allelopathy is when one plant secretes a chemical into the soil that suppresses nearby plants. These species “appear to be agents of change” (R. A. Henderson 2003) because of the effects they have on overall species diversity by reducing the dominance of a few species.
There’s more than soil and roots under that grass. Most of us associate fungi with rot and decay. Some prairie fungi play this role. However, other fungi are vital to the survival of some plants. The roots of many prairie plants have a mutualistic relationship with mycorrhizal fungi. These are fungi that penetrate into or wrap around plant roots. They send strands out into the soil called hyphae. The plant gives the fungi carbon from photosynthesis and the fungi provides chemicals from the soil that the plant may have trouble obtaining, especially phosphorus. The fungal hyphae increase the functional surface area of the root and can aid in water absorption. Mycorrhizae may also benefit host plants by improving defenses against grazers and defending against pathogenic fungi (Wilson and Hartnett 1997).
Some species, such as certain orchids, are especially dependent on mycorrhizae. There are at least seventy-five species of fungi associated with eastern prairie fringed orchid across Illinois and Michigan (Zettler and Piskin 2011). Orchids are one group of plant that may need mycorrhizae for seed germination and plant establishment.
The ability of the dominant grasses such as big bluestem and Indian grass to exploit these symbiotic relationships may be a large factor in explaining their competitive ability. When researchers suppressed fungi, the dominant grasses declined and other species became more abundant (Wilson and Hartnett 1998; Hartnett and Wilson 1999).
They are small, but there are a lot of animals down in the soil also and they may have major effects aboveground. Invertebrates may consume up to 40 percent of the annual production of roots and there may be a greater mass of earthworms than cattle on the prairie (Joern 1995). Grazing belowground is different than grazing aboveground. Water enters plants through root hairs and leaves plants through tiny holes in the leaves called stomates. When leaves are grazed, there are fewer holes to lose water. When roots are grazed, there are fewer roots to absorb water. Losing roots may be more detrimental to the water balance in plants than losing shoots.
Flint Hills prairie has at least 228 species of nematodes in the soil (Orr and Dickerson 1966). There are 470,000 nematodes per square foot under little bluestem in South Dakota mixed-grass prairie (Ingham and Detling 1984). Those nematodes consumed more overall grass biomass than prairie dogs and bison. In many grasslands, nematodes “constitute a major portion” of the prairie fauna (Smolik and Lewis 1982). An acre of prairie soil may contain 1.2 million earthworms; 405,000 macroinvertebrates; 202.4 million microinvertebrates; and 22.3 billion nematodes (Ransom et al. 1998).
Before Euro-American settlement, approximately 52,860,000 acres of prairie covered Iowa and Illinois (Samson and Knopf 1994). If we assume the same relative densities of soil invertebrates across those two states, that gives us 64,200,000,000,000 earthworms; 21,400,000,000,000 macroinvertebrates; 10,700,000,000,000,000 microinvertebrates; and a whopping 1,177,000,000,000,000,000 nematodes in the prairie soils within Iowa and Illinois.
Earthworms leave numerous channels that allow air, water, roots, and other invertebrates to move through the soil more easily. Earthworms will pass through their gut 10 percent of the total soil organic matter in the top six inches of soil (James 1991). Put another way, earthworms could consume and pass through their gut the entire upper layer of soil every decade.
The surface horizons of the prairie soils are, in actuality, invertebrate fecal material, intertwined with living organisms of every trophic status. (Clearly, Mom was right when she told us to go wash our hands following any soil explorations!) (Seastedt 1995)
When roots die, they also leave channels in the soil. Earthworms and other invertebrates can follow these channels and enlarge them. This allows both air and water into the soil and provides pathways for soil organisms to move. In native prairie, approximately a quarter of the root systems are replaced each year (Dahlman and Kucera 1965). That’s a lot of death and turnover and decaying roots leaving channels between the soil particles. That’s also a lot of carbon added to the soil every year.
Ideally, soil should be 50 to 60 percent particles and 40 to 50 percent pore space. Depending on the soil type, time of year, and when it rained last, those pores will be taken up by some combination of air and water.
While the soils are open and porous, the soil particles are also chemically cemented together into aggregates. Much of the humus that increases aggregation of soil particles comes from decaying roots (Weaver 1947). Early settlers cut bricks from sod and built sod houses, or soddies. Some of them stood for decades. That’s how well aggregated those soils used to be. It’s hard to imagine forming the soil in a modern cornfield into a brick and that brick surviving a rainstorm.
Although there are dozens of other elements in soil besides the carbon derived from photosynthesis, perhaps the most important element from a plant’s perspective is nitrogen. The nitrogen cycle is very complex because nitrogen can take so many forms. There is nitrate (NO3-), nitrite (NO-), nitrogen (N2), ammonium (NH4+), and ammonia (NH3) to name some of the most important compounds. Denitrification is the conversion of nitrate to nitrogen. Fixation is the conversion of nitrogen to ammonia. Nitrification is the conversion of ammonium to nitrate. Mineralization is a multistep process where organic nitrogen, nitrogen in carbon containing molecules, is converted to inorganic nitrogen that can be taken up by plants. Immobilization is when soil microbes take up nitrogen compounds. Clearly, studying nitrogen requires a specialized vocabulary.
While modern society requires expensive power plants and fossil fuels to capture nitrogen for fertilizers and other uses, in the prairie much of the same work is done with flowers and bacteria. Specifically, members of the legume family have a bacteria called Rhizobium in nodules along their roots. The root nodules provide a safe habitat and carbon for the bacteria while the bacteria are able to break that tough chemical bond and create usable forms of nitrogen for the plant.
So why is nitrogen important to plants? First, the nitrogen atom in these compounds can have a range of electrical charges, from -3 in ammonia (NH3) to +5 in nitrate (NO3-). Numerous microbes are able to use these changes from one chemical to the next and changes in the charge on the nitrogen for energy (Schlesinger 1991). Nitrogen is one of the most important elements in proteins and amino acids, critical to all forms of life.
As complex as the prairie is in the sunlight, with blossoms and bees and butterflies and bison, the unseen prairie below our feet may be as complex, and probably more diverse.
Only Gravel Ridges Are Poor Enough
WE ARRIVED AT OUR favorite gravel hilltop prairie late in the morning late in the month of April. It was a chilly 43 degrees with a stiff southern wind trying to disperse the clouds overhead. A merlin flashed off the fencepost as we pulled up. Not a classic prairie bird, but a good sign. The pasqueflowers were in bloom, so it was worth the long drive this morning.
This is a sandy, gravelly, steep-sloped hill prairie between two large wetlands. It’s a tiny islet in a sea of row crops. From up here we can see for several miles in every direction. What we see is bare dirt and the little stubble that hasn’t been disced under yet. There’s one tractor working the fields, a rooster tail of dirt blowing away behind it.
The grasses and flowers under our feet may have once felt the hooves of bison or elk, but the roots and soil never felt the rip of a steel plow. Those roots below and blanket of leaves above have held the soil together for all these centuries.
The pasqueflowers were just beginning to open when we arrived. We drove down to another nearby prairie and oak savanna to hike and birdwatch for a couple hours. When we came back around noon, we could almost watch the flowers open as the day continued to warm. We walked a circuit, checking several flowers every ten minutes or so. There were noticeable changes with each check until the petals had fully opened.
As the air temperature warmed and the flowers open, the air becomes alive with I don’t know how many bees. They seem to be buzzing everywhere and each looked different to my uneducated eye. These pasque-flowers are the only plants blooming for several miles in every direction. How does this little hilltop have enough nectar and pollen this time of year to sustain this diversity and abundance of bees? Where are they coming from, and where are they going next? Do they know the world beyond this hilltop or has this hilltop been the sole home for countless generations of these bees?
Much of this book is about change. The prairie has changed over the millennia since the Pleistocene. There were occasional floods and extended droughts. There were blazing hot summer days and bone-chilling winter nights. Sunny days gave way to afternoon thunderstorms. Blizzards came out of nowhere. Fires swept the prairie on a regular basis. Herds of wildlife grazed the grasses and trampled the soils. With the coming of the plow, the prairie was lost in a few short decades. It was gone before anyone noticed, except for a few hard to get to and out of the way places like this hillside.
In a couple days, the prairie smoke will bloom. In another couple weeks the fluffy, wispy seedheads of both pasqueflower and prairie smoke will be blowing in the wind. These are maybe the only two prairie flowers that are more recognizable as seedheads than flowers. Soon green grass will grow up through brown. Blue-eyed grass, ground plum, and puccoon will follow shortly, and by mid to late summer these will be followed by sixty or more additional species.
Today’s changes occur by the hour and minute. From cool to warm, from quiet to buzzing, from closed to open. No visit to the same prairie is ever the same.