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Five Points to Know About Soils
Jethro Tull isn’t just a 1960s and 1970s rock band. An English agriculturalist by the same name lived in the 1600s and 1700s. He loved to till the soil. And till. And till some more.
“He believed the more you tilled, the better the soil,” says Aaron Daigh, a North Dakota State University (NDSU) soil scientist. Tull reasoned that the tiny soil particles caused by tillage pulverizing the soil would be easier for plants to suck up as they grew.
Fortunately, farmers and soil scientists have come a long way since those days. Still, there are some points about soil that often fly under the radar. Here are a few that Daigh and Jodi DeJong-Hughes, University of Minnesota (U of M) Extension crops educator, discussed at last month’s Strip-Till Expo at NDSU/U of M research sites near Fergus Falls, Minnesota.
1. Yes, the rocks on many upper Midwestern soils brought by glaciers thousands of years ago are a pain. Still, farmers who farm these soils can consider themselves fortunate. Farmers in many areas of the Dakotas and Minnesota have some of the best soils in the world. “Up here, it is amazing how black and deep the soils are,” Daigh says. He compared that with bright red soil of western Arkansas (where he grew up) that just had 1 to 2 inches of topsoil.
2. There’s a downside, though, to farming deep and rich soils. “You can abuse these soils and not see the effects right away,” says DeJong-Hughes. One way to check if soils are being battered is to fly over them during the growing season. “If the crop is doing better in the wheel tracks (of the tractor and planter), you are doing too much tillage,” she says. “It’s making the rest of the soil in the field fluffy. She’s coined the term ‘Fluffy Soil Syndrome’ for this scenario.
3. Hazy Day? Blame the Clay. Those windy and hazy days are often due to the clay particles that have become detached from the soil. Meanwhile, detached sand and silt particles gravitate to ditches.
4. Well-structured soils are chocked full of benefits. “Roots move through them quickly,” says DeJong Hughes. “They like the path of least resistance.” Meanwhile, soils with excellent soil structure contains plentiful pores that promote excellent water and gas exchanges. So how do you build soil structure? “Cover crops help,” DeJong-Hughes says. “So do (more intense) crop rotations. Adding manure is fantastic for the soil.”
5. Unfortunately, tillage will break down soil structure with whatever form of tillage you choose. This even includes the slight tillage used in no-till to make way for the seed. Field operations performed on excessively wet soils can have decade-long soil structure consequences. DeJong-Hughes and Daigh cite a 1981 trial in Finland where a tractor-trailer combo drove over excessively wet plot areas. Twenty-nine year later, Nordic researchers performed a computerized topography (CT) scan of soil samples pulled at a 0.9 to 1.2 foot depth. CT scans were compared with a control soil that dried before field traffic passed over it.
After nearly three decades later, the soil structure of the areas through which the tractor-trailer was still damaged. The researchers noted the damage would have been worse today, as equipment is larger. Read a study summary here.
Realistically, farmers are sometimes backed into a corner during wet falls. They face a tough choice between harvesting on wet soils or letting corn linger over winter. Fortunately, upper Midwestern farmers have a soil compaction buster better than any deep ripper.
“Around here, there are extreme winter lows and summer highs, the biggest spread in continental North America,” says Daigh. “When our soils crack when it is dry, it can easily go 8 to 9 feet below the ground. That is the best form of deep tillage.”