By Jessie Haas
“Plants manage water, and in managing water, they manage heat,“ according to Australian agricultural pioneer Peter Andrews. This has been born out in a recent study showing that widespread use of cover crops in the Midwest has affected the local climate, producing cooler temperatures and more abundant spring rains.
Previously, farmers practiced summer fallow, leaving fields bare through an entire year between wheat crops. This was thought to benefit soil moisture and interrupt pest life cycles. In fact, what it did was burn up soil carbon, damage the moisture-holding capacity of the land, and increase local heat the same way a parking lot does. Fine dust particles rose into the sky, forming a haze that held heat in but did not nucleate rain. Soil expert Peter Donovan wrote in Recognizing the Soil Carbon Sponge that landscapes of this kind “multiply heat and aridity.”
Cover crops, in contrast, shade the soil. The plants transpire water, which forms high convective clouds, and then rain. Local temperatures are cooled by the rainfall. As the clouds dissipate, longwave heat rays escape into the upper atmosphere.
It is all part of how the the soil carbon sponge functions. Soil is one of the major sinks for carbon, and as such is an increasing focus for climate change activists. When plants store carbon in the soil, it gains structure, becoming rich and porous, with air-holes and channels that can also store tremendous amounts of water. In The Drought Resilient Farm, Kansas farmer Dale Strickler wrote of driving past his own farm after a tornado. The ditches around other farms were full of brown water. His were empty. His land, after years of soil-building, had retained all that water and was ready to put it to work.
How do we understand carbon and its relation to climate change? Donovan said that there are two different views. “They do not contradict each other, and it is not about right or wrong here, but these two embody different possibilities or outcomes.”
One view sees this essentially as a math problem. There is too much carbon in the atmosphere. Much of that excess was oxidized out of the soil and can be put back there through changes in farm practices. If we also reduce emissions, we can change the equation and stabilize climate.
The other view sees the carbon and hydrological cycles as linked, part of what Donovan called “the solar-powered circle of life.” Carbon removed from the atmosphere and stored in the soil disproportionately affects the earth’s heat balance at the surface level – where we live. Carbon built into soil structure holds water, and moist soils are cooler. The moisture supports plant life; plants shade the soil, cooling it further. Plants also transpire moisture, cooling the air around them. Trees are big air conditioners. So are grasslands and fields planted to cover crop. The transpired moisture carries bacteria to the upper atmosphere; raindrops nucleate around the bacteria and fall, cooling us again, and bringing more moisture, in a virtuous cycle.
This cooling, moistening, and increased plant productivity happen right down at ground level where we can feel it, making life pleasant as we do the work we must do, to reverse the carbon imbalance.
The hydrologic cycle has a powerful effect on climate change, one that has drawn less attention than the carbon cycle. This may be in part because it feels more difficult for humans to influence. But thinking about the soil carbon sponge gives us a way to understand how we influence the clouds. Soil is something we can build and improve, on a scale from vast rangelands to small back yards. Wherever soil organic matter increases, the soil carbon sponge becomes more healthy and begins to improve the hydrologic cycle. Knowing this, we can begin to dance with the rain, the plants, and the soil microbes to increase the beauty and hospitable nature of our earthly home.
Jessie Haas has written 40 books, mainly for children, and has lived in an off-grid cabin in Westminster West, VT since 1984, www.jessiehaas.com. Links available with the posting of this article on the GET website.