Carbon in the Garden

We hear the word carbon thrown around a lot: carbon copy, carbon footprint, carbon life forms.
 
But what is carbon, and what does it have to do with gardening?
 
Carbon is an element found in all living things. In fact, carbon is second only to oxygen in our bodies.
 
Carbon can take many forms. It can be the graphite in your pencil, the diamond on a wedding ring, a gas, or a liquid. It is also found in the compost, manure, and plants in your garden. That adaptability, paired with its ability to bond easily with other atoms and molecules, is probably why we find it almost everywhere, including in our garden.
 
How plants use carbon
 
Carbon is fundamental to life as we know it. Plants pull carbon dioxide from the air to use in photosynthesis in a process called the Calvin cycle. Carbon is also used to make cellulose.
 
Cellulose is what gives plant cell walls their structure. Combined with lignin, pectin, and a few other materials, carbon is what holds trees and plant stems upright.
 
Did you know that the cotton fibers in your T-shirt are one of the purest forms of cellulose? I didn’t either.
 
Carbon in the soil
 
Soil carbon is a term used to describe the amount of solid carbon found in soil. That carbon comes from inorganic carbonate minerals. It also comes from all the carbon-based life forms living in and on the soil, like beetles, microorganisms, and worms. When those creatures poop or die, their carbon becomes part of the soil organic matter that plant roots call home. The same is true of neighboring plants. As they decompose, their carbon is stored in the soil. Carbon improves soil structure and keeps plants healthy and productive.
 
It’s been that way for millions of years. Until recently.
 
Commercial farming and deforestation have created problems regarding soil carbon. The use of heavy machinery and excess digging kicks carbon into the atmosphere as carbon dioxide, contributing to climate change and reducing soil carbon levels. Reduced carbon levels also impact the effectiveness of nitrogen fertilizers. Or maybe it’s the other way around.
 
Research conducted at the University of Illinois at Urbana-Champaign discovered that farmed soils have shown a significant reduction in soil carbon levels since farmers started applying synthetic nitrogen fertilizers in the mid-1950s. The more nitrogen that was added, the more carbon was lost from the soil.
 
Fertilizers cost money. We don’t yet know if adding the fertilizer makes plants grow more quickly than the soil carbon can be replaced, or if it is something else. Too much nitrogen creates nitrogen pollution, as well. For me, this stresses the importance of lab-based soil tests. Our plants need nitrogen, but too much of a good thing can easily become a bad thing.
 
And lost soil organic matter translates into lost water. Healthy soil needs carbon, microorganisms, and time to process and store water effectively.
 
Putting carbon back into the soil is not a simple matter of burying some charcoal or using biochar. These things are delicate chemical interactions.
 
How to retain soil carbon
 
We can help our garden soil retain the carbon our plants need and reduce the amount of carbon lost to the atmosphere with the following tips:

• Add fruit- and nut-producing trees, shrubs, and perennials to your landscape.
• Avoid digging and rototilling when unnecessary.
• Consider transforming your lawn into a meadow or letting the grass grow taller.
• Improve biodiversity in our gardens and garden soil.
• Install more native plants.
• Protect soil against erosion with cover crops and green manures.
• Use compost and aged manure to fertilize your plants and return some carbon to the soil.
• Use fewer or no chemical pesticides and herbicides. They negatively impact biodiversity, and their production generates greenhouse gases.
• Use lab-based soil test results to only add necessary fertilizer.

 
We can improve soil health and soil carbon levels with just a little effort. I think it’s worth it.