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Iowa’s soil condition quality slipped in past 50 years

By Staff | Jul 3, 2009

Soil researcher Jessica Veenstra using the Gidding's Probe, a truck-mounted device for soil sampling.

Iowa is known for its rich, dark soils, but studies are showing that although our topsoil is still prevalent, it’s not as high in quality, and is more compacted, as it was a half a century ago.

Jessica Veenstra, a graduate student currently working on her doctorate degree in soil science at Iowa State University, looked into soil studies that were conducted 50 years ago and then compared them to her own recent samples.

Veenstra said she referred back to the National Resource Conservation Service’s soil studies that were conducted in the 1950s and 1960s then repeated those statewide samples.

“I went back to the original sites that had been surveyed from when very early soil maps were made,” said Veenstra. “I sampled soils and did the same sorts of analysis and compared them to find how the soils have changed or not changed over time.”

Some of the original locations were a challenge to find, she said, but with the help of aerial photos she was able to pinpoint most samples within six feet of their original locations.

The global positioning system was used to mark the exact locations for future reference as well.

“My research will just show another point in time for someone else to compare it to,” said Veenstra.

What Veenstra found was that although the topsoil depth has remained the same over the last 50 years the quality has decreased.

According to Veenstra Iowa’s topsoil has moved from hilltops and higher elevations down slope most likely due to runoff which has resulted in hilltops that have lost topsoil layers while valleys have gained.

It’s this average of loss on hilltops and higher elevations to gains in topsoil in the lower valleys that are resulting in topsoil depth remaining the same.

The quality of Iowa’s soils, Veenstra said, is lower mainly due to how tightly it is packed. Veenstra said she examined how soil particles are arranged in soil profiles in prairie remnants – areas that have never been cultivated, such as cemeteries. She said undisturbed soil has a granular structure that is like a sponge. Air and water moves easily through the soil because density is very low.

Today, due to many years of tillage, the soil is now much more dense and water and roots don’t move through it as easily, she concluded.

Veenstra described Iowa’s soils in the 1950s much like a glass of marbles. Between the marbles, she said, are many air pockets and spaces. When soils are arranged like this, air, water and roots could move through much easier than the soils of today that are more compacted.

“The topsoil might be at the same depth, but the quality is not as good,” said Veenstra. “It’s very interesting what humans’ impacts on the soils (are) by how they change them.”

Veenstra said it’s hard to predict just what problems, if any, the results of her research will indicate. Some of the impacts may be compensated through improved land management technology.

“In addition to decreases in topsoil quality we’re seeing increases in technology with hybrids, for example,” said Veenstra. “But then again there could be many problems associated with lower quality topsoil in terms of production.”

Mike Sucik, state soil scientist, said that if producers are having concerns about their soil conditioning to contact their local county NRCS office.

“The NRCS is rewarding farmers for management systems that increase soil carbon and reduce soil disturbance,” said Sucik. “There are also incentives in the Environmental Quality Incentive Program that will reward producers for adopting continuous no-till practice.” No-till is often credited with improving soil conditioning.

According to Sucik, there are a variety of ways to maintain or improve soil quality and he recommends reducing or eliminating tillage; diversify crop rotations by adding small grains, hay crops and cover crops; and stop planting row crops on steeper grounds.

Contact Kriss Nelson by e-mail at jknelson@frontiernet.net.

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