Catherine W. Idzerda" />

Over-tilling can cause more harm than good

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Catherine W. Idzerda
Monday, April 18, 2011
— It’s a message nobody wants to hear.

Your beloved rototiller, the machine that grinds soil into cake flour, creating a garden surface as smooth as a well-made bed, is often bad for soil.

Bad for soil means bad for plants.

“There’s no difference between a crack pipe and a rototiller. Both are tools of the devil,” said Jim Stute, crops and soils agent for the UW Extension, Rock County. “Both provide instant gratification that leads to addiction, and that addiction causes long-term damage.”

Holy soil scientist, Batman! Is it that serious?

Yes, but most people don’t want to believe it, even after Stute explains, very slowly, the science behind it.

Soil science 101

Soil is made up of three particles: Sand, silt and clay.

Now imagine one of those big baskets of balls that are sold in big-box stores—stay with me, this is important.

Sand particles would be like a basket of beach balls; silt particles would be like a basket of tennis balls and clay particles like a basket full of marbles.

Sand particles have a lot of pore spaces, making it easy for water to pass through. Clay particles have tiny pore spaces and are able to store water for plant use.

All three of those particles glued together form what’s called a soil “aggregate,” an ideal medium for growing plants. The aggregates combine the best properties of the individual particles.

Larger pores between aggregates encourage root growth, giving the plant the ability to collect nutrients from the soil. They also facilitate the exchange of gases for plant roots—oxygen in, carbon dioxide out.

Smaller pores within the aggregate store water and protect microbes, which are responsible for processing nutrients into forms that plants can use.

Rototilling 101

It’s spring. You’ve dragged the rototiller out of the shed, tuned it up, gassed it up and are ready to create a garden worthy of a Martha Stewart magazine spread.

“This is how the beast does it,” Stute explained. “Most of them are power driven, so they go at a constant rate across the ground. But the tines go around relatively fast, and get multiple kicks at each aggregation.”

Often, people make repeated passes across the garden beds.

The result?

“Those aggregates get beat to dust,” Stute said.

Remember—or go back and re-read “Soil science 101”—those aggregates are crucial to the health of the soil.

Rototilling exacerbates a soil’s inherent problems, Stute said.

Trouble with clay? You’ve made it worse.

Trouble with sand? Worse still.

Here’s something else that happens in the spring: rain.

“The rain has a significant impact on the soil surface and further breaks up the aggregates,” Stute said. “It further detaches the clay particles.”

As a result, a hard crust forms on the surface of the soil, causing gardeners to—wait for it—get out the rototiller to break up the crust into soft soil, adding insult to aggregate injury.

Repeated rototilling at the same depth can create a hard pan of soil that restricts root growth.

Sticky issues

Soil aggregates pounded to dust don’t stick themselves back together.

Soil microorganisms feed on organic matter—compost, manure, cover crops—that have been added to the soil. This process forms the “gum” that sticks the particles together.

That’s good, but not good enough.

“This gum is the Elmer’s glue of microbial gums,” Stute said. “It’s water soluble.”

The real magic, Stute said, happens when fungi that are already in the soil work with plants to improve water and nutrient uptake.

The waste product of that process is glomalin, a non-water soluble glue that holds aggregates together.

When you over-rototill soil, it harms the very fungi that create this nonsoluable glue.

Bottom line

For Stute, the problem isn’t the machine itself but the way it’s used.

“The judicious use of a rototiller is OK,” Stute said.

Yes, you can use it to prepare a seed bed in the spring.

“You want good soil to seed contact,” Stute explained. “The intimate association between seed and soil helps the seed draw water in.”

Rototillers also can be used to blend in organic matter such as composted manure or dried leaves.

Stute advises people with small gardens to spade in the materials with a shovel.

If you must use a rototiller, be sure to keep it shallow.

Preserving the health of the soil will also cut down on your gardening costs. You won’t need to apply as many fertilizers.

Remember, healthy soil means healthy plants.

Last updated: 4:57 pm Thursday, December 13, 2012

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