Book Report: The Soil Will Save Us
Back in January, I attended the Arlington Friends of Urban Agriculture meeting as the topic was "Climate Change, Agriculture, and Our Food." I'm interested in how the reality of climate change will continue to affect us and how we as gardeners should adapt our practices for the health of ourselves, our gardens, and the planet. It was a fascinating meeting that discussed how rising temperatures affect plants, insects, and microorganisms, including plant pests and diseases. The final speaker introduced how the techniques of regenerative agriculture use plants to extract carbon dioxide from the atmosphere, sequestering carbon in the soil.
The New York Times article linked above is fantastic, but for further discussion, I highly recommend reading The Soil Will Save Us by Kristin Ohlson. Both the article and the book talk about larger scale farming, so as I read them both, I took notes about what's relevant to a small-scale home gardener. Here are my notes:
Bare land starves soil life. Healthy soil is very much alive, teeming with insects and other tiny invertebrates, fungi, protozoa, bacteria, etc. Diversity is important, as all living things play roles in their communities that benefit the larger ecosystem. To keep that soil community healthy, we have to feed it. Dead stuff (compost and mulch) are important, but living plants are better. Why?
Plants "leak," feeding soil life with sugar. Through the process of photosynthesis, plants absorb atmospheric carbon dioxide and transform it into sugar. This sugar is food for the plant, but plants only use a small fraction of the sugar they produce. Some sugar is stored in fruits or other parts which is why apples and carrots are sweet. A lot of sugar ends up in the soil, excreted through the plant's roots. As Ohlson puts it, "plants leak." The soil life feeds on these sugars and they provide benefits for the plants in return: microorganisms and fungi "poop" minerals and other nutrients that plants need in a form that can be absorbed by the plants' roots.
As carbon accumulates in the soil, it becomes more fertile. It's called humus and it makes the texture of soil spongy and cake-like. Nearly every gardener has at least one broken shovel horror story involving compacted clay soil. You see, microscopic clay particles are uniform in size and shape, so they tend to stack up like a pile of bricks. Humus particles are the antidote, as they are irregularly-shaped and therefore resist compaction. Instead, spaces form between the particles in soils high in humus, allowing air and water to move freely. Thanks to these open pores, the soil can absorb more water under flood conditions, store water, and release that water back to plants in times of drought. So as the weather gets weirder due to climate change, the home gardener's low cost crop insurance is soil enriched with compost and mulch, which gets digested by the soil life and redeposited as humus.
Carbon in exposed soil reacts with atmospheric oxygen, where it escapes into the atmosphere as carbon dioxide. This is another reason to keep soil covered. Again, to actively sequester carbon, living plants are required as dead plants don't engage in photosynthesis and leak carbon sugars. Dead plants (mulch) are effective to protect soil carbon while feeding soil life. Of course, mulch has to be reapplied as it breaks down. A living groundcover of plants continues to feed the soil life for the duration of the plants' lives.
I'm going to keep my compost bin and keep adding compost to my garden beds to feed the soil instead of synthetic fertilizers. I will continue mulching my garden beds with straw to cover the soil between plants. I'm going to keep vegetable gardening year-round as more gardening = more photosynthesis = more carbon sequestration. Meanwhile, the paths between the beds are covered with perennial ground cover (mostly clover) that feeds the soil life by releasing carbon sugars into the soil while feeding the above ground pollinators with nectar and pollen from its flowers.