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Farming: Farmers hold the key to cooling the planet, the soil carbon sponge

13 Mar 2020

Farmers create the cooling effect by improving their soil’s ability to absorb and hold rain leaving green plants in the soil longer and by increasing the organic matter (carbon) in their soils.

Last time we talked about holding onto the rain that falls by retaining it in the soil. How that reduced flooding and erosion, keeping sediment out of the waterways. This time we look at the impact of holding onto rain in the soil and its impact on cooling the planet.

Dr Walter Jehne, famous soil microbiologist and climate scientist, spoke at the Organic Regenerative Agriculture Conference at Lincoln University last weekend and again at Otago University yesterday. I heard him both times.

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According to Dr Jehne, “The answer lies in the soil where trillions of microbes are working away exchanging minerals and proteins for carbon with the plants.” (Abridged).

“It comes down to a farmer’s ability to use diverse pastures, not monocultures of rye grass and clover, rotating farm animals leaving a lot more residual pasture behind than with traditional grazing, providing diversity strips of flowing plants for insects and birds, mixed in with farm forestry where you have the right tree in the right place (not monocultures of Pinus Radiata).” (Abridged).

“The grazing animals are fertilizing the ground and the dung beetles are converting that dung into soil humus (carbon). The grazing animals trample significant amounts of green matter into the top layers of the soil and the microbes and worms convert that into humus too. Large mobs of animals are needed to lay the leaf down to help the mulching process. The remaining leaf starts photosynthesizing immediately the animals leave the paddock.” (Abridged).

As the soil’s carbon sponge deepens it holds more of the rain that falls and the growing season lengthens. “Elongating the green period is key to cooling the planet.” Dr Jehne did the maths for us on the transfer of heat energy and believe me, in simple terms, the sun either heats the bare ground which radiates infrared heat back heating the atmosphere, or, it hits growing plants which turn that heat energy into carbon via photosynthesis, cooling the planet.

“Re-radiation of the sun’s energy is by far the biggest contributor to global warming there is,” says Dr Jehne.

Keeping growing plants in the ground all the time is key to maximising the cooling effect that plants have. And the microbes need plants to feed off so good to keep that sugar flowing as long as possible in the season.

“The problem with farming in New Zealand is the dry,” noted one of the most experienced farmers in the room.

70% of the sugar (carbon) produced by the plant during photosynthesis is used to build the leaf, stalks and root of the plant with the rest (30%) going directly to the soil microbes in exchange for all the soil goodies that the soil microbes provide the plant. A truly symbiotic relationship.

40% of the carbon goes into building the top infrastructure of the plant which either gets eaten, trampled or kick-starts the recovery round of photosynthesis. Either way, more than a third of that gets recycled back into soil carbon underground (the poo). The bit that doesn’t get recycled is the bit that builds animal protein which ends up leaving the farm on its way to our plate.

The other 30% builds roots, the pathway for soil microbes to get carbon and for the plant to get nutrients.

Photosynthesis – the miracle of life

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Six molecules of water + six molecules of carbon dioxide (+ sunlight and plants) = one molecule of sugar + six molecules of oxygen.

What could be more amazing? This is the basis of all life on our planet. We depend totally on allowing this to work unhampered. Nature at work.

Farmers and foresters are the key to this process and so long as they work with nature and not against her, and increase the quality and depth of the soil sponge, they achieve a wide range of benefits for all of us, including cooling the planet.

See Dr Jehne and his Rebuilding the Soil Carbon Sponge video shot at Harvard University in 2018 here.

Keep asking great questions …

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