ATHENS, Ga. — As climate issues capture governmental and public attention — from the effects of methane emissions to weather extremes — it is incumbent on the world to take action.
Specialists in disciplines throughout the University of Georgia are pursuing research to mitigate climate change, and experts in the College of Agricultural and Environmental Sciences (CAES) are focused on helping residents address climate challenges in ways that will benefit the environment and ensure both profitability and sustainability for members of industry.
Primary among these efforts is providing research-based information and outreach to enable individuals and producers to assess the environmental impact they can have locally, regionally, nationally and globally.
Carbon in the soil
Aaron Thompson, professor of environmental soil chemistry in the Department of Crop and Soil Sciences, is participating in international working groups using large datasets of soil properties to try to understand what is governing the amount of organic matter in the soil — and how that might change as a function of land management.
Adapting land management practices in different agricultural systems — row crops, pastureland, etc. — can be an effective way to maximize the amount of organic matter in the soil, he said.
“However, the term ‘soil carbon sequestration’ is often interpreted to mean carbon is trapped in the soil permanently. This is not the case. Some portions of the ‘sequestered carbon’ can remain in soil for even thousands of years, but most carbon is cycled on much shorter timescales and needs to be continually replaced to maintain a high soil-carbon content. A lot of my work focuses on understanding at a micro or even molecular scale what causes carbon to persist in soil for a long time,” Thompson said. “Organic matter sticks around in soil for essentially two reasons — first, it can become attached tightly to mineral surfaces, actually chemically fused with the minerals, much like old grease can become stuck on a frying pan, and then the organic matter will stay there until the mineral dissolves. Second, the organic matter can end up somewhere in the soil where microbes and enzymes cannot reach it. This might be very deep beneath the surface where there are very few microbes to break it down. Or the organic matter might get trapped inside small aggregates of clay-sized minerals that have no places for microbes or enzymes to enter. In these case, that organic matter will persist until the aggregates break apart or the soil is disturbed and microbes or enzymes can get to it.”
In conventional tillage systems, that organic matter is brought to the surface, where it degrades and carbon is released into the atmosphere.
“It’s not necessarily that the tillage is bad, it just breaks up that structure and exposes parts of the soil and organic matter that have been essentially hiding from microbial activity. For instance, if you switch to a pasture-based system from an annual crop system, and you go from tilling every year to maintaining continuous pasture that you do not till, you’re going to increase the amount of carbon and organic matter in the soil. But keeping the organic matter there is going to depend on you maintaining the system. If you then switch back to tilling every year, you’re going to slowly begin to lose that carbon again.”
One of the most studied solutions to address agriculture’s carbon impact is the use of cover crops.
At CAES Research and Education Centers and experiment stations, scientists are studying the impact of various cover crops and conservation tillage practices — such as strip tillage and no-till systems — on hundreds of acres around the state.
The primary purpose of a cover crop is to enhance the life and the function of the soil, replacing nutrients depleted by crops, preventing erosion, and keeping rainfall or other water running through the soil from leaching residual nitrogen into waterways, said Miguel Cabrera, the Georgia Power Professor in Environmental Remediation and Soil Chemistry in the CAES Department of Crop and Soil Sciences.
For areas like south Georgia, where the hot climate and sandy soils make it difficult to retain organic matter in the soil, practices like cover cropping can both increase the organic matter in the soil and offset some CO2 emissions.
Cover cropping is slowly gaining traction in Georgia, said Cabrera, giving the example of a farmer who has been using the system for more than 20 years.
“He started thinking he was just trying it out because he needed to do something different to protect the soil,” Cabrera said. “He said that after a couple of years or so, he sold most of his tilling equipment because he didn’t need it anymore. He also said he did not have to irrigate as much with the mulch on the surface because it protected the water from running off.”
Cabrera believes that the key to more widespread adoption is the distribution of research-based information through Cooperative Extension programs — and raising awareness of U.S. Department of Agriculture federal assistance that can help producers adopt more sustainable practices.
Estimating the fix
It can be challenging, however, for producers using cover crops to estimate how much nitrogen is released into the soil and how much of the cover crop remains in the soil, eventually contributing to soil carbon.
“When we use cover crops that are legumes, like crimson clover, they fix nitrogen from the atmosphere. When those cover crops are terminated, typically sometime in March or April, they will decompose and release some of that nitrogen for the subsequent crop,” Cabrera said. “One of the things we are working on is a model that estimates the amount of nitrogen that the cover couple releases, but also how much cover crop biomass, which is equivalent to how much carbon is left in the soil.”
Over the past six years, Cabrera has been part of a team that has developed an Agricultural and Environmental Services Laboratories website application that allows growers to enter specific data about their cover crops — including the type, termination date, cash crop being planted over the cover, etc. — and combines that information with environmental data from UGA weather stations to estimate how the cover crop decomposes and how that impacts the soil.
“We’re expanding the Cover Crop Nitrogen Availability Calculator in cooperation with the University of North Carolina, the University of Maryland and the U.S. Department of Agriculture Agricultural Research Service into the mid-Atlantic area and the Atlantic Coast states. We are also moving more into the Midwest because researchers and producers in that area are becoming more interested in cover crops,” Cabrera said.
While cover crop usage is still somewhat limited in Georgia, UGA Cooperative Extension agents in county offices can have a tremendous influence on the adoption of cover crops in their area.
“County agents who are very gung-ho about cover crops and who push them in their counties increase the number of farmers who use cover crops. Ideally, we would have more of our producers move in that direction,” Cabrera said.
Carbon credit is another carbon-offset system that has growing popularity in the U.S., particularly in the West.
“There are a couple of companies that are working with farmers to provide assistance to establish methods to sequester carbon on farms,” Cabrera said. One example is a fertilizer company that produces a large amount of nitrogen each year, requiring a great deal of energy produced from fossil fuels. By developing a program that would encourage farmers to sequester carbon on their farms, they are trying to “balance” their carbon footprint in pursuit of carbon neutrality.
“If they can show that they’ve encouraged farmers to adopt methods that will sequester carbon, they can get to the point where they can measure how much they are releasing against how much they are able to sequester through these programs. They may have a high energy generation profile, but they can show that they have this program that is actually fixing a lot of this carbon and that it’s balancing that,” Cabrera said.
Agriculture and climate
Pam Knox, an Extension agricultural climatologist who produces UGA’s daily climate blog, said there are two sides to the climate issue in agriculture — what agriculture does to climate and what climate does to agriculture.
“There are a lot of different things going on in agriculture, including land use changes such as plowing up the ground to have bare soil to plant (row crops) but also the draining of wetlands and changing over time from more bare-ground crops to more forests,” Knox said. “Forests and agricultural crops, like anything else, all have different effects on climate.”
In addition, the required inputs for crop production — irrigation, chemical weed and pest control, fertilization — must also be factored into the climate and resource-use equation.
“We are changing the land in different ways, and they don’t all impact climate in same way. Agriculture uses a lot of water and the use of fertilizer, pesticides and herbicides all impact soil nutritional levels. When you plow, that land is more susceptible to erosion and, if it rains a lot, can leach those chemicals into the waterways and cause water-quality issues,” she said.
Conversely, changes in climate are increasingly affecting agriculture.
“The Southeast is more insulated than other parts of country from climate change. It is called the warming hole and, for whatever reason, this region has not experienced as much change as other parts of the country,” Knox said. However, that trend is changing. “Georgia’s temperature averages went down between 1925 and 1960, but that has changed and now we are on the same path. Georgia temperature averages have gone up 3 degrees Fahrenheit since 1971.”
Ironically, that rise in temperature is due in part to the passage of the federal Clean Air Act, which reduced the amount of soot and aerosols in the atmosphere. As the air has gotten cleaner, temperatures have warmed due to increased penetration of sunlight through the atmosphere. This gradual change in temperature has an impact on the region’s growing season.
“For every degree Fahrenheit in temperature rise, the growing season increases by about a week. That is both good and bad,” Knox said. “An extended growing season means a farmer has more potential to grow hybrids that take advantage of that or they can double crop — put in one crop early, harvest it, then put in another crop for the second half of the growing season. That can cut a farmer’s risk by creating two income streams, but on the other hand, a longer growing season means there is more time for weeds, pests and diseases to establish.”
Because the temperature increase in the Southeast is mostly happening at night and not during the day, there is a corresponding rise in humidity, which can contribute to an increase in fungal plant diseases.
“Temperatures have been changing since 1960. Nighttime temperatures are getting warmer twice as fast as daytime temperatures,” Knox said. “And although annual average precipitation has not changed much, we know that the way the rain is falling has changed. We have more high-intensity short bursts — say 2 inches in a day — that are more frequent, and more dry spells between rain events, which is stressful for crops.”
Extension in action
Knox is encouraged by the “huge initiative” in Extension to talk about the impacts of climate change, including the National Extension Climate Initiative, as well as the focus on climate mitigation and resiliency through the Association of Public and Land-grant Universities.
“There are a lot of opportunities here. Farmers are looking at ways to incorporate solar (energy production) into farm production to save money. Farmers using cover crops are putting less fertilizer on the ground, using less irrigation and saving on fuel. A lot of the changes that are really going to be necessary can economically benefit the farmers,” she said. “When we talk about agricultural practices to address climate change, we have to recognize that farmers are running a business and they have to be able to survive. There has to be a partnership and we have to make sure producers are right there in the conversation.”
–Maria M. Lameiras, University of Georgia