One way to make healthy topsoil and therefore healthy plants and food is to add compost and use mulches. For even better results, in addition, keep green plants growing on the soil for as long as the season will allow.
Green plants use sunlight, carbon dioxide, and water to produce carbohydrates, proteins, organic acids, and other carbon compounds. This is photosynthesis. The green plants keep a portion of the carbohydrate (or “sugars”, or “organic carbon”) to support their own growth and health. When grown in the garden and on the farm, they are eventually eaten by people and other animals.
At the same time, another portion of the plant’s carbohydrate travels through the roots into the soil to attract and feed and multiply the beneficial soil microbes living near their roots, such as nitrogen-fixing bacteria and mycorrhizal fungi. In return, the soil microbes deliver water and nutrients - including hard to find essential trace elements - to the plant. It is a happy two-way street.
All this is good, but it gets better. The microbes fed by the roots also create stable humus, which holds plant nutrients, buffers the soil pH, and increases the soil’s ability to hold and deliver water. In addition, humus holds carbon, and lots of it, and in this state the carbon is good for the soil and for plants. We have too much of this stuff in the air, but no longer enough of it in the soil due to conventional growing methods.
This "regenerative" form of farming and gardening has achieved phenomenal results in soil building, food production, and carbon sequestration.
So how does the backyard/community gardener grow great plants and save the world from climate change at the same time? Here’s how:
Avoid tilling the soil because it destroys/harms microbes and releases carbon to the atmosphere;
Keep the ground covered with a variety of green plants for as long as the season will allow;
Use compost, mulch, and organic fertilizers to feed microbes and protect soil structure;
Grow predominantly perennials, shrubs, and trees in the ornamental garden. Use annuals in pots and as fillers in the perennial beds;
Most vegetables are annuals. Don’t pull the pea and bean and other plants when you’ve picked the crop. Let them build soil for a while. Then practice chop and drop, or pull and drop. Cover the garden with a mulch of leaves for the winter;
If you have the space, consider cover crops to improve the garden soil;
Never use chemical pesticides or fertilizers, unless you want to reverse everything you’ve gained from doing the above.
An excellent website for more information on building healthy soil, growing more nutritious food, and storing carbon is www.amazingcarbon.com . Prominent soil bio-chemist Christine Jones has a focus on agriculture, but her articles and videos certainly apply to gardening as well.