The soil solution: To combat climate change, consider the problem from the ground up

AS THE WORLD suffers bouts of extreme weather conditions, including record-breaking temperatures, torrential rains and prolonged droughts, many people may be thinking about how to make changes. But few may consider that the ground beneath them might hold the answers.

Arnab Bhowmik, Ph.D. does.

As the director and lead researcher of the Soil Sustainability Lab in the College of Agriculture and Environmental Sciences, he knows that building healthy soil is the solution to combating global climate change.

“Soil health is an affordable and safe solution to ensure food security and environmental sustainability,” Bhowmik said. “How can you expect to have healthy plants, humans, animals and the environment if you don’t have healthy soils? Everyone and everything you do is linked to the soil. If we can enrich soils by improving our actions, we can have a major effect on this global existential crisis and adapt better to climate change.

“We need to change the way we see soil, which is usually just seen as a medium for plant growth, and see it as a solution to climate change.”

In addition to providing us with food, fiber and fuel, soil filters water; feeds and hosts growing forests, crops and other plants; provides a home for numerous organisms; contributes to biodiversity; supplies most of the antibiotics used to fight disease and regulates the earth’s temperature. Bhowmik said.

As part of influencing climate, soil cycles carbon and nitrogen in the form of greenhouse gases, like carbon dioxide, methane and nitrous oxide, the three major gases from the agriculture sector that trap heat in the atmosphere and make the planet warmer. When soil is healthy, it acts like a sponge and soaks up the carbon and nitrogen that could otherwise be circulated into the atmosphere, contributing to the greenhouse gas problem.  In addition, storing carbon and nitrogen in the soil makes it more fertile for plants and sustains life.

Due to long-term overuse and exploitation – mainly over-planting, over-grazing and too much tillage – our soil’s health has been degraded and its ability to do its job hindered.

“When we degrade this valuable resource, we are releasing the stored soil carbon back into the atmosphere,” Bhowmik said. “As researchers, we need to look at how we can help the soil capture more carbon and for it to stay protected in the soil longer.”

Soil is the second largest natural carbon “sink” after oceans, according to United Nations’ Food and Agriculture Organization. The process of keeping the carbon in the soil for the long term is called carbon sequestration. Carbon serves as food for numerous microorganisms and is, therefore, the currency of soil health. It also provides the capacity to the soil to provide key functions, such as water retention, structure and fertility.

Carbon dioxide is a major component of the atmosphere. But when humans produce more carbon dioxide than can be naturally removed by processes like photosynthesis, there is an excess. The annual rate of atmospheric carbon dioxide’s increase over the past 60 years is about 100 times faster than previous natural increases. Much of this is due to burning fossil fuels and soil degradation.

But carbon dioxide is not the only greenhouse gas to be worried about, Bhowmik said; there’s also methane and nitrous oxide, which are 24 and 300 times more potent than carbon dioxide, respectively.

Agriculture – particularly livestock and soil management – is responsible for 11% of greenhouse gas emissions. So, one way of reducing GHG is to make sure we manage soils to convert them from a source to a sink of GHG. This can only happen if the soil is healthy.

“We need to stop treating soil as dirt,” Bhowmik added. “Dirt is dead soil. Adding carbon to it makes it soil.

“When we can start realizing and respecting the critical role soil plays in our existence, we will be able to use its full capacity and potential.”

With multiple grants and collaborations with national partners, Bhowmik and his team are designing various climate-smart soil management practices that make soil resilient and resistant to the climate crisis. For his research and teaching efforts in soil health, Bhowmik received the 2020 A&T Rookie Researcher and the 2022 A&T Jr. Excellence in Teaching awards, among multiple other recognitions.

Hemp and Hemp-derived Biochar: Climate and soil impacts

Nationwide interest in hemp farming exploded with the passage of the 2018 Farm Bill, making hemp a legal crop. Hemp accumulates biomass faster than any other row crop and, as such, can capture 15 tons of atmospheric carbon dioxide per hectare, making it a strong candidate for building soil organic carbon.

Bhowmik, along with other researchers at N.C. A&T and the Center for Environmental Farming Systems (CEFS) in Goldsboro, wanted to know how to use the leftover residues of harvested hemp plants after extracting cannabidiol (CBD), a phytochemical with medicinal properties. The goal was to see if adding these residues in different forms could make soil microorganisms more resilient to climate change, as observed by multiple wetting and drying conditions.

For this purpose, they collected different types of soils from the A&T research farm (Piedmont soils) and CEFS (coastal soils) of North Carolina. They added hemp residue or hemp residue-derived biochar to it and compared it with hardwood biochar (a product that is typically used in the area). What they found was that hemp residue and hemp biochar occasionally improved soil microbial enzyme activity through the various soil types and moisture cycles. This change was more distinct in the sandy as compared to coastal soil. On the other hand, the hardwood biochar consistently led to a decline in soil nutrient cycling regardless of soil type or moisture cycle. This work was recently published in PLOS One journal as a peer-reviewed article.

While additional work needs to be done, it appears that farmers growing hemp can use all plant components, including the hemp residue and hemp biochar, to adapt their soils to the changing climate while improving their soil health.

In addition, Bhowmik and a team of researchers are also looking into how additions of these products along with hog waste can influence soil carbon storage and GHG emissions, including carbon dioxide and nitrous oxide. While hog waste, a persistent issue in North Carolina, contains harmful contaminants, if co-applied with biochar, could the waste have value in helping to improve soil health?

“These are the kinds of questions we are asking,” Bhowmik said.

Compost and Cover Crop Hemp Field Trials

Cover crops are grown for purposes other than harvesting. Some legume cover crops are used to fix and add nitrogen to the soil. Through multiple experimental field trials at the A&T research farm, Bhowmik and his group evaluate how to grow hemp organically using nutrients cycled from cover crop residues and compost.

“This would tremendously decrease chemical fertilizer costs for our limited resource farming and at the same time add more carbon to the soil by improving soil health,” Bhowmik said.

Another component of this research is to see how these organic sources of fertilizers (cover crop residues and compost) interact to influence greenhouse gas emissions from soil. Research leading to this work was published by Bhowmik in the journals Frontiers in Microbiology, Ecological Applications, Agriculture, Sustainability and Open Agriculture.

Inclusive soil health actions require all of us to participate

With various projects happening simultaneously, Bhowmik knows his work requires a long-term commitment, but it’s work that has to continue.

“When you look at civilizations that have been obliterated, if you go back and examine what was happening, you’ll see that one of the major reasons was poor and unhealthy soil,” he said. “Without healthy soil for food, you have to migrate to a place with richer soils.

“When we no longer have a place to go, when we run out of places where we can find healthy soil, we are in trouble. We can no longer exist. This is an existential threat to us all.”

And while all of us can’t be researchers, we all still have a role in helping to keep soil healthy and keeping the earth functioning, he added.

“As consumers, we have a role to play,” Bhowmik said. “We can make good choices about the food we buy and what we eat. We have to be ready to pay a premium price to support sustainability. We have to be willing to buy local food and support our local farmers. The time to act is now.”