To till or not to till

Question: I understand that tillage can be harmful to soils. So, if that’s the case, why do farmers till soils?

gardener-tilling

A freshly tilled garden soil. Photo courtesy of Chiot’s Run (www.flickr.com/photos/chiotsrun/)

Answer: Till, plow, cultivate–these words all describe the practice of using tools to move soil particles around, cut slices into the soil, push the soil aside, or even turn the top layer upside down.

For centuries, people made small holes in the soil to plant seeds. They pulled weeds by hand or used hoes to remove weeds from gardens and fields. Sometimes they used a shovel to mix something into the soil. The Native Americans taught the new settlers in North America to bury a dead fish in a hole and plant seeds on top of it.

More recently, farmers used plows and planters pulled by teams of animals. Now they use tractors. Gardeners often use rototillers that pulverize the soil.

So, why do farmers and gardeners till soils?

There are three main reasons:

1. Incorporation: To mix fertilizer, plant residues, or other materials such as compost or manure into the soil.

2. Seedbed preparation: To make soil conditions favorable for planting seeds.

3. Weed control: To uproot weeds or destroy their root systems.

In dry places, sometimes farmers also use special tillage practices to harvest water and limit evaporation from the soil surface.

But a better question is, “Do farmers really need to till soils?”

dust-bowl-resized

The 1930s Dust Bowl moved dramatic amounts of soil—enough to bury this farm machine. Photo: NOAA/Dept. of Commerce.

The Dust Bowl in the United States was caused by a combination of drought and too much tillage that left the soil surface powdery, bare, and dry. When the wind blew, it took the precious topsoil with it. We learned that plowing too much hurts the soil. Specifically, it decreases the amount of organic matter in the soil, which then decreases the ability of a soil to form and maintain aggregates (natural clods), and to resist erosion.

So, scientists and researchers began looking for ways to protect the soil. In the last 50 years, scientists have learned that leaving plant residues on the soil surface protects soil from the destructive effects of wind and raindrops. We also learned that when we stop disturbing the soil, it begins to recover, the organic matter level increases, and the soil resists erosion better.

Many farmers now use tillage systems that minimize the amount of soil that’s disturbed in order to leave plant residues on the surface. There is also equipment that can plant seeds in soil that has not been plowed.

Though many people are concerned about using chemicals to kill weeds, this method of weed control protects the soil from the harmful effects of tillage, and there is less erosion. Other specialized equipment injects fertilizer into the soil while limiting the soil surface disturbance.

no-till-corn

Corn planted into no-till corn residue near Minden, Iowa in 2008. Photo: Natural Resources Conservation Service

In reality, once most soils are tilled, they are not quite as healthy as they once were. And so the next time, they may need tillage again to create a good seedbed.

Farmers and gardeners should learn from researchers and scientists who encourage people to use less tillage when possible.

In the end, this makes most soils healthier.

–Answered by Clay Robinson, a.k.a., Dr. Dirt

Have a question for Soils Matter? Post it to the comments section below or email us at soils-matter@soils.org

2 responses to “To till or not to till

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