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Stewardship of the Earth: Carlo Moreno

Soils and climate change

The top three feet of the world’s soils contain almost three times as much carbon as the entire atmosphere, highlighting the importance of the soil ecosystem in the global carbon cycle. Recent research has pointed to the buildup of soil organic matter, or decomposing plant and animal tissue, as a key feature in improving the soil’s capacity to sequester atmospheric carbon dioxide. Here we will focus on two practices that can greatly increase soil organic matter: cover cropping and composting.

Cover crops

Plants are one the largest terrestrial sinks of carbon on the planet. Through the process of photosynthesis, atmospheric CO2 is pulled out of the atmosphere and stored in the tissue of plants. This stored carbon is then moved into soil organic matter through the death of plant roots and from litter deposited from plant shoots. Soil microorganisms are responsible for long term storage of carbon by converting organic matter into humus, which is a very stable form of organic matter that is resistant to further decomposition.

While trees are often considered the largest biological sinks of carbon on the planet, planting annual plants as cover crops can be just as important. A cover crop is a term used for any plant that is grown in between harvests, when most growers will leave their soils bare. In farm settings, cover crops such as crimson clover, cereal rye, and oilseed radish have all been shown to increase soil carbon over time (https://www.sare.org/publications/cover-crops/ecosystem-services/cover-crops-at-work-increasing-soil-organic-matter/).

The power of compost

A recent study in Global Change Biology has suggested that while cover crops can increase carbon levels in the upper most foot of the soil profile, the key to long term carbon storage lies in the addition of composts (https://www.sciencedaily.com/releases/2019/08/190814161818.htm) . Composts supply an important source of macro and micronutrients to soil microbes that aid in the formation of humus. Without compost, these same microbes will opportunistically breakdown any remaining reserves of soil organic matter, and in the process, release carbon back into the atmosphere in the form of respiration. The study goes on to recommend that carbon conscious growers should complement cover crops with soil amendments such as composts, manure, and leaf matter.

Additional citations:

No till soil carbon sequestration rates published- https://www.sciencedaily.com/releases/2014/04/140418161344.htm

Tree planting has potential to increase carbon sequestration capacity on Nation’s forests-