Sequestering Carbon in Soils
The Organic Center partnered with Northeastern University to explore how organic impacts carbon sequestration in the soil.
Healthy soils are the backbone of our food system. Without them, we wouldn’t be able to grow most of our food, because around 95% of the food we eat is produced by our soils. It’s not just important for the food on our table, it’s also important for clean water, healthy ecosystems, and our climate.
Soil is the world’s largest water filter, and provides filtration via physical, chemical and biological processes that remove or degrade various pollutants in water as it passes through the ground. When water passes healthy soils water filtration is improved which means fewer pollutants in our rivers, streams, lakes, ponds and aquifers.
In addition to helping preserve clean water, soils are the base of the food web, and without them many organisms and the complex of life that depend on them wouldn’t survive. Soil dwelling insects and fungi are food sources for larger animals and the organic matter that decomposers break down is essential for all plant growth.
Eighty percent of the Earth’s terrestrial Carbon is stored in soils and other than the ocean it is the largest pool of carbon on earth. Humans manage the majority of the Earth’s soils and research shows that our management practices can deplete the soil’s carbon stores – releasing it back into the atmosphere – contributing to global climate change. Agriculture in particular has been linked to large losses of soil organic carbon worldwide. In fact, a recent article published in the Proceedings of the National Academy of Sciences, shows that agriculture worldwide had resulted in a loss of 133 billion metric tons of carbon from the soil. They also found that the rate of carbon loss from agricultural soils has increased dramatically over the last 200 years as more land is converted to crop and rangeland.
Fortunately, a number of studies suggested that organic practices can actually increase the carbon pool in our soils – making soils part of the climate change solution. These techniques include extended crop rotations, rotational grazing, fallowing and the use of manure, compost and legume cover crops to manage soil fertility and are likely the same factors driving the increased levels of humic substances we found in organically managed soils.
However, most of these studies have been too small-scale to make large-scale comparisons of organic practices to conventional ones. Both organic and conventional farmers use a wide variety of management techniques. From different soil amendments to different crops to different tillage strategies, farms vary widely in how they implement strategies that impact their soil. Because organic farms are regulated by the United States Department of Agriculture, they do have several things in common that are important for soil building. For example, they cannot use synthetic fertilizer to provide nutrients to their plants. Instead, they must use things like compost, manure, and nitrogen-fixing plants (that are then incorporated into the soil) to manage their soil nutrients. These techniques can increase soil organic matter, and are relatively consistent across organic farms.
This study looks at organic and conventional farms in a way that incorporates all of the differences in farming practices, soil types, crops, and other variables to get a big-picture view of how organic impacts carbon sequestration in the soils.
This study uses novel methods to examine not only carbon sequestration in over a thousand soil samples taken from across the country to understand the impact that organic farming has on soil carbon.
We contacted over 8,000 organic farmers, and measured over a thousand soil samples from across 48 US States.
The results from this project show that organic farms store more carbon in the soil, and keep it out of the atmosphere for longer than conventional farming methods.
This study looks at over one thousand soil samples from 48 US states, comparing levels of the long-term, stable pool of soil carbon, in organically and conventionally managed soil. The study also measured total soil organic matter and humification, the process by which organic matter is transformed from labile organic matter into more stable humic substances.
The study found that organic soils had higher levels of all soil organic matter. Specifically, organically managed soils had 13% higher soil organic matter and 44% higher long-term carbon storage.
These results highlight the potential of organic agriculture to increase the amount of carbon sequestration in the soil, contributing to climate change mitigation.
Dr. Geoff Davies, Northeastern University
Dr. Elham Ghabbour, Northeastern University
Dr. Jessica Shade, The Organic Center
Dr. Tracy Misiewicz, The Organic Center
The Organic Center
Farmers Advocating For Organic