Why carbon-rich dirt helps your garden — and the Earth — thrive
- A single teaspoon (1 gram) of rich garden soil can hold up to one billion bacteria, several yards of fungal filaments, several thousand protozoa, and scores of nematodes
- The less we disturb soil structure by tilling, the less we destroy or disrupt soil life
- One of the ways that we can reduce greenhouse gas accumulation in the atmosphere is to sequester CO2 in our soils and plants.
Garden soil care and health can make a difference.
There is a good reason to want healthy soil and that is to have a better garden, as healthy soil is basic to have a thriving landscape and garden. Soil is alive, and there are lots of microorganisms in the soil in addition to the earthworms that make soil function for growing plants.
According to Kathy Merrifield, a retired nematologist at Oregon State University, a single teaspoon (1 gram) of rich garden soil can hold up to one billion bacteria, several yards of fungal filaments, several thousand protozoa, and scores of nematodes; see: https://extension.oregonstate.edu/news/secret-life-soil.
In most soils, there are mycorrhizal fungi that have symbiotic relationships with plant roots providing nutrients to plants and in return getting shared food from the plants. These fungi also facilitate moving carbon from plants and storing it in the soil. Hyphae, the threadlike filaments of mycorrhizal fungi, are coated with a sticky substance called glomalin, which is instrumental in the storage of carbon. The U.S. Department of Agriculture advises land managers to protect glomalin by minimizing tillage and chemical inputs and using cover crops to keep living roots in the soil.
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One of the things that I have learned through gardening is that the less we disturb soil structure by tilling, the less we destroy or disrupt soil life. I used to work up my garden soil each spring with a tractor and disc and/or with a rototiller. I probably killed a lot of earthworms and destroyed lots of other life or disrupted it with that approach, but I did also add carbon by discing undercover crops and this is a reasonable way to do that.
Another way to break up the soil in the absence of cover crops is to use a broadfork or spading fork, which breaks up the soil more gently. It can help add compost, which will drop into the cracks created.
We have also reduced life in the soil using chemicals — fertilizers, herbicides, and pesticides. I can say that I am not guilty of that as I have gardened organically for many years and have never purchased a chemical fertilizer; instead, I rely mostly on compost or organic fertilizers. One of the things I learned growing up on a farm in the ’50s was the importance of alternating crops. Grain crops were succeeded by clover or alfalfa, which would fix nitrogen and add organic matter when plowed under. For all the above reasons, using cover crops in the garden if possible is a good practice.
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There are other aspects of soil that are important as well.
Once upon a time, a great deal of carbon was stored in our soils before the advent of agriculture. Much of this carbon has been oxidized to CO2 upon years of cultivation since agriculture was begun. We cut forests, plowed up prairies and degraded natural ecosystems to create an agriculture-based civilization.
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Losses of soil carbon are estimated at 133 billion tons since agriculture began 12,000 years ago and the rate of loss is the highest since the industrial revolution. However even with all this loss, there is still more carbon in soils than in the atmosphere and in all plant life combined; there are 2,500 billion tons of carbon in soil, compared with 800 billion tons in the atmosphere and 560 billion tons in plant and animal life. Unfortunately, in 2020, vast forest fires contributed the equivalent of 2.6 billion tons of carbon dioxide emissions to the atmosphere, according to Global Forest Watch.
One of the ways that we can reduce greenhouse gas accumulation in the atmosphere is to sequester CO2 in our soils and plants. Scientists are working hard to understand how we can best accomplish this. Under the Paris accords on climate change, this statement was advocated in 2015 for soil sequestering: “If we increase by 4 ‰ (0.4%) a year the quantity of carbon contained in soils, we can halt the annual increase in CO2 in the atmosphere, which is a major contributor to the greenhouse effect and climate change.”
This is a great goal, but reaching it is difficult with 500 million farmers and others to be persuaded that this should be done and teaching them how to do it. As gardeners, we can add only a small amount of carbon to our soils compared to farmers, but every bit helps and we can and should compost our kitchen waste, leaves, and lawn clippings to make compostand use it liberally. Happy better gardening with compost.
If you have a gardening-related question, you can contact the UC Master Gardeners at (209) 953-6112. More information can be found on our website: http://sjmastergardeners.ucanr.edu/CONTACT_US/.