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The Difference Between Soil and Dirt: Why We Must Protect Farmland Now

American farmland and the soil of which it is made are some of the nation’s most valuable natural resources. Like all resources we must consider how we as a people manage and preserve what we have for future generations.

We often use the words soil and dirt interchangeably, but when it comes to farming, there is a crucial difference between the two. Dirt describes any mix of organic matter, rocks, and minerals, while soil is a layered, biologically-active composition capable of supporting plant growth.

Thus, all soil is dirt. But not all dirt is soil.

It is difficult for us to appreciate the complex structures and ecosystems of soil, because all of this activity takes place underground. Over time natural forces act upon the earth to create layers of soil (known as horizons) where organic and mineral materials mix together. These layers develop pore spaces with interconnected pathways that bring air and water to roots, insects, and microbes that result in optimal growing conditions for crops.

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The Problem of Overuse and Development

Our nation’s food security is rooted in good soil. Sadly, we continue to lose some of our best soil every year to overuse, erosion, and development. While the effects of overuse and erosion can be reduced and even reversed with proper land management practices, the effects of development are much more difficult to correct, as residential and commercial construction quickly turns fertile soil into nearly unusable dirt.

When arable land is converted to non-farm use, such as commercial buildings or residential housing, the construction process both churns and severely compacts the soil. In order to build homes and roadways, the rich, delicate top soil layer is stripped and the subsoil is compacted to create a firm foundation.

It takes hundreds or thousands of years for soil horizons to develop from parent material beneath, but it can be destroyed in a matter of hours by heavy excavation equipment. Once disturbed, it takes centuries for natural forces or decades of expensive rehabilitation to recreate the ideal conditions suitable for plant growth.

For example, compaction alone can reduce crop yield by more than 60 percent. The center of the field below was purposely compacted to demonstrate its effect. Note the stunted corn plants struggling to grow alongside the larger, healthier plants around them.

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The Loss of American Farmland

As mentioned in our previous post, the area of arable land with quality soil has decreased significantly over the last century. According to a study done by American Farmland Trust, the United States is losing farmland at a rate of 2.9 acres per minute. Below is a rather shocking visual depiction by AFT of land lost to development between 1992 and 2012.

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In just 20 years’ time, the United States lost the equivalent of all the farmland in Iowa! Much of this land also contained our most productive and resilient soil that can never be reclaimed.

Ways to Protect Farmland Now

Farmers can begin to implement principles of conservation agriculture to combat overuse and erosion of prime soil, while those looking to sell can do everything in their power to ensure that their land remains farmable. This includes working with buyers who are dedicated to the continuation of agricultural production.

Every one of us can support American Farmland Trust and other organizations that are working with farmers to preserve U.S. Farmland. Additionally, individuals can help preserve farmland directly by investing in it themselves.

Every acre purchased is an acre saved.

Information and data sourced from "What is Soil?" by Learn Geology and "Farms Under Threat: The State of America's Farmland" by American Farmland Trust.