Show-Me soil sense
“Out of the long list of nature’s gifts to man, none is perhaps so utterly essential to human life as soil.” That was the assessment of Hugh Hammond Bennett, the first chief of what is now known as USDA’s Natural Resources Conservation Service (NRCS) and widely considered the father of soil conservation.
Soil is the foundation of our natural world and the lifeblood for agriculture, whether growing crops or raising livestock. Yet not all soils are created equal. Soils are classified by differing characteristics and behavior to help make wise land use decisions, whether farming or building a house, digging a well or constructing a highway.
The variability of soil is especially evident in Missouri. The Show-Me State is made up of more than 500 different soil “series,” which is the lowest category of the national soil classification system and the common reference term used for soil map units. The diversity in soil makeup accounts for Missouri’s diversity in agriculture.
“Soil type will drastically affect what you can grow, how you grow it and how productive you can be,” said Landry Jones, MFA conservation grazing specialist. “It’s different for every grower and for every operation.”
If there was a star of these series, it would be Menfro, named Missouri’s official state soil in 2004. More than 780,000 acres in 40 counties have been identified as Menfro soil, which is very productive for farming. This type of soil was formed on wooded upland and slopes along the Missouri and Mississippi rivers and their major tributaries.
The distribution of the Menfro soil overlaps into many of state’s six major ecoregions, which are further broken down into 28 more detailed ecoregions. Jorge Lugo-Camacho, Missouri state soil scientist with NRCS, explains the regions in simple terms using I-70 as the dividing line.
“North of I-70, the soil is more suited for growing row crops,” he said. “There is less sloping, roots can grow deeper, and the soil holds onto moisture better. In many of those areas, the deep soil is high in organic matter, good for growing corn and soybeans. One limitation of this area is the central claypan areas, like in Audrain County, which can limit yields of some crops.”
The ecoregions of the north include Central Irregular Plains, Western Corn Belt Plains, and Interior River Valley and Hills, where Menfro is prevalent. Northwestern Missouri has deep, dark prairie soils, which contrast with the light-colored and stony soils of the Ozarks. As the color and depth vary, so does the fertility, Lugo-Camacho said. In some areas, the soil can produce 70 bushels of corn while other areas can only produce shrubs and trees.
Making regional recommendations
MFA agronomists who consult with growers across these regions must know how to deal with a wide range of soil types, said Davin Harms, precision manager for districts 3 and 6, which includes areas in northeast and east-central Missouri.
“We have heavy clay pan soils that can be productive but require timely rains to deliver the highest yields,” Harms said. “Soils with higher clay content and higher cation exchange capacity values require different management from a fertility aspect. We factor that into the fertility recommendations we make, especially for potassium. Most of the areas I cover tend to have more acidic soils that need to be amended with lime to raise soil pH to create better plant growing conditions. The Missouri river bottoms are the exception as they tend to have higher soil pH, which creates issues and management concerns with phosphate applications.”
South of I-70 there are more soil limitations for crops, but the area is abundant with forests, grasslands, natural springs and sink holes, explained Lugo-Camacho. The Central Irregular Plains soil series spills into this region. With soil derived from cherty carbonate rocks, the Ozark Highlands makes up two-thirds of the region.
“The shallow soil has low pH and the bedrock and hardpan, known as fragipan, make it difficult to grow crops,” he said.
In the Bootheel, the Mississippi Valley Loess Plains and Mississippi Alluvial Plain regions have a wide range of soils, along with a warmer and longer growing season that allows a variety of crops to grow.
As Garrett Christian, MFA precision manager for district 10 in this region, described it, “We have blow sand all the way to heavy gumbo and everything in between—sometimes versions of that all in the same field. Sandier soils in the Delta can bring peanuts, potatoes, peas and melons into play. These same fields may have cotton, corn and soybeans in the rotation as well. Heavy ground may have rice with either corn or soybeans also in the rotation.”
Using input intelligence
These crops have different fertility demands, which can be affected by various rotations, Christian said.
“For instance, peanuts fix nitrogen, so corn and cotton following peanuts can require less added nitrogen fertilizer to achieve the same yield goal,” he explained. “The need to account for this in cotton is more magnified because you can have too much nitrogen.”
Sandy soil offers its own set of challenges, Christian continued.
“One example would be potassium,” he said. “Many growers wait until spring because they are afraid of leaching when applying potash on sand. There is work being done to help figure out just how much it can actually hold.”
When talking with producers about forage production, Jones said understanding the farm’s soil type is crucial to determining what species will grow best.
“If they have rocky ground or shallow soils, just 5 or 6 inches before hitting bedrock, I typically increase the rate of little bluestem and sideoats grama,” he said. “If they have good, deep, productive soils that are also kind of dry and sandy, then big bluestem and Indiangrass work well. If the producer has wet clay that holds water or drains poorly, then I look at planting switchgrass and gammagrass. But to find the most productive forage, you really need to understand the soils on the farm.”
Knowing soil type is also vital when applying herbicides, said Doug Spaunhorst, MFA director of agronomy. He pointed out that herbicide labels categorize soils more broadly into coarse, medium or fine texture.
“It is important to consider the soil texture, the distribution of sand, silt and clay particles that make up the soil colloid,” Spaunhorst explained. “For example, clay soils like to hold on to herbicides in the same way they like to hold on to water particles. Rainfall and temperature also influence herbicide persistence and soil pH.”
Saving the soil
Jones pointed out that NRCS offers science-based soil information to help farmers, ranchers, foresters and other land managers effectively manage and conserve their most valuable investment—the soil.
“The health of that soil is what our industry is built on, and we have to take care of it,” he said.
The USDA offers four principles to promote soil health. First is to minimize soil disturbance by limiting tillage, using proper chemical input and rotating livestock. The second is to maximize the soil cover year-round by planting cover crops, leaving plant residue and using organic mulch. Third is to expand biodiversity above and below ground by using diverse cover crops and rotations as well as integrating livestock. The fourth principle is to boost the presence of living roots, which help reduce soil erosion and provide food for microbes and earthworms.
“I don’t necessarily believe that cover crops are the panacea, but I do believe they hold soil,” Scott Wilburn, MFA senior staff agronomist, said. “Drive around in the country during a heavy rain and compare the runoff from the fields with a cover crop or wheat to the fields that are worked clean. It’s dramatic. Soil is foundational to all we do, so anything that protects it should be utilized.”
Missourians have long known the importance of soil health and show it through their funding of soil and water conservation by supporting the 0.1 of 1% Parks, Soils and Water Sales Tax. First approved in 1984, Show-Me State voters have continued to renew the tax on the ballot every 10 years.
About 50% of the tax revenue is designated to saving soil and protecting the state’s water resources. Most of those dollars help agricultural landowners through voluntary programs developed by the Soil and Water Districts Commission and administered by the Soil and Water Conservation Program through district boards in Missouri’s 114 counties.
It’s an effort that Hugh Hammond Bennett would no doubt be proud to see as today’s growers and agronomists continue his quest to preserve the soil, and in turn, preserve life itself.
“Sustainable management practices will improve soil health,” Lugo-Camacho said. “Mother Nature is very good at healing degraded soil, but we must do our part.”
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