The Dirt on Soil

The standard dictionary definition of soil is usually pretty straightforward: a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles, or: a mixture of mineral and organic materials which is capable of supporting plant life.  We recognize it when we see it and nod in agreement when reading the definition. And yet the term "soil" can bring up many different reactions, depending on how we're approaching it. 

In our urban setting, we tend to relegate soil to the sidelines and keep it contained in borders. Sometimes the sight of it spilled onto our walkway can look, to our eyes, like a stain on our favorite shirt. We just want it to stay put and fade into the background. Or, we think of soil as something "out there" in the farmlands of the midwest, not really anything that involves us in our daily lives. 

To gardeners and farmers, especially those committed to organic practices, the condition of the soil is key to yielding an excellent harvest. We check the pH and add amendments as prescribed. We increase the organic matter in our soil by adding compost, leaves and wood chips. These materials feed the soil food web of microorganisms that render nutrients available for plants to uptake and use for growth. We talk about "my soil" as we might refer to our children or pets, its good and bad characteristics. 

As a student in my first soil science class I learned that soil is formed over time by climate and biological processes weathering rock, dependent on geological position in the landscape. This is a concept of immense proportions. I dutifully listed weathering, climate, etc. on the quiz but I truly did not grasp its global implications. And I don't fully grasp it today. This takes TIME to make! This stuff that we plow up, pave over, push to one side, move from site to site, this is the living medium that is the foundation of life on earth? 

Lately, soil has come to forefront in the discussion about climate change, carbon sequestration and what can be done to slow the accumulation of greenhouse gases in the atmosphere. In addition to the carbon dioxide pulled from the atmosphere by growing plants, soil is a great storehouse of carbon. Different forms of carbon in the soil are more or less recalcitrant, meaning that they are in a stable form that does not easily volatilize to carbon dioxide. The use of pyrolysis, a no/low oxygen technology of converting crop waste and logging slash into biochar, which is then buried in the soil, is showing promise for large scale carbon sequestration. Methods of farming such as no-till also keep greenhouse gas emissions such as carbon dioxide and nitrous oxide from entering the atmosphere. 

Soil, our weathered rock and organic matter, can play a big part in ensuring planet health for the next generation. I am given hope by the knowledge that dedicated and intelligent minds are working on this and that our students will have hopeful and meaningful work, finding solutions to climate change. 

Dirt: The Ecstatic Skin of the Earth by William Bryant Logan is a thoughtful book to learn more about the soil (dirt!) beneath our feet!