The fertile top layers of soils keep disappearing, a new study shows

By Roberta Attanasio

Plants grow in and out of soils—and sustain almost all living beings on our planet, either directly or indirectly. But soils are rapidly disappearing from farms all around the world, threatening our ability to grow food. The treasure beneath our feet is continuously subjected to erosion and degradation, mostly resulting from intensive farming practices.  

Relentless tilling, for example, allows weeds control by turning the soil over, but leaves it bare and vulnerable to wind and rain—causing the loss of the fertile top layer. Even the famed black Iowa soil is disappearing.

“In Iowa they call it ‘black gold’—a fertile blanket covering the landlocked Midwestern state. Thousands of years of prairie grass growth, death and decomposition have left a thick layer of dark, organic matter on the vast plains. When European-American settlers first began ploughing in Iowa, they found the weather and local geology had combined this organic mulch with sand and silt to form a nutrient-rich type of soil called loam. It gave Iowa one of the most fertile soils on the planet and enabled it to become one of the largest producers of corn, soybeans and oats in the United States over the last 160 or so years. But beneath the feet of Iowa’s farmers, a crisis is unfolding.”

This crisis is best exemplified by the results of a new study showing that an area of nearly 100 million acres in the Corn Belt has completely lost its carbon-rich topsoil, also called A-horizon soil. The Corn Belt is an area in the midwestern United States that includes all of Iowa and parts of Minnesota, Wisconsin, North Dakota, South Dakota, Missouri, Illinois, and Indiana. The study points out that, until now, the true extent of topsoil loss has been underestimated.

A-horizon soil’s upper portion—rich in organic matter—is critical for plant growth because of its water and nutrient retention properties. “It’s worth being clear here. The authors aren’t talking about reduced soil fertility or loss of mineral nutrients. They’re talking about the complete removal of the medium in which crops are grown—the utter bankruptcy of the organic richness that lay for centuries under the tallgrass prairie.” 

The study also shows that the A-horizon soil has primarily been lost due to tillage erosion—the downslope movement of soil caused by the conventional way of preparing the soil for planting, which is based on digging, stirring, and turning it over. Thus, the authors urge the adoption of no-till farming methods.

“Agriculture is often cast as an environmental villain, its pesticides tainting water, its hunger for land driving deforestation. Worldwide, it is responsible for nearly a quarter of all greenhouse gas emissions.”

Unsurprisingly, the study authors found that erosion of the A-horizon soil transfers large amounts of carbon dioxide from the hillslopes to the atmosphere. They advocate the switch from intensive conventional agricultural practices to soil-regenerative practices, so to allow atmospheric carbon dioxide to be again sequestered in soil—in other words, to take carbon dioxide out of the air and put it back in the ground—while at the same time restoring the soil productivity.

Regenerative practices mimic nature’s regenerative forces. No-till agriculture—instead of plowing and disturbing soils along with the organisms that call them home—uses direct seeding through the stubble of the previous year’s crops. Undisturbed soil resembles a sponge held together by an intricate structure of roots and soil organisms—it resists erosion.

Head to the Kiss the Ground website to learn more about regenerative agriculture.