In organic agriculture, nutritional building blocks like nitrogen, carbon and phosphorous are introduced via organic matter to improve soil over time. But when these nutrients are released as gases into the air or in stormwater runoff, they can pollute water sources and contribute to greenhouse gas buildup.
For farmers, the loss of valuable nutrients affects the bottom line because they must be replaced with more costly inputs.
Comparing various farming systems
Washington State University scientists Ann-Marie Fortuna, Craig Cogger and Doug Collins are developing a series of experiments to determine the types and amounts of gases emitted by organic cropping systems.
"We are going to work out a set of practices that give growers a way to manage inputs that give plants the nutrition they need while not creating pollution," said Cogger, a soil scientist and extension specialist based at WSU's Research and Extension Center in Puyallup.
"To that end, we are comparing how different organic farming systems with a history of different amendments and tillage frequency affect releases of carbon dioxide and nitrous oxide, two major greenhouse gases," he said.
Microbes the focus of research
"We know that both tillage and type of amendment affect the soil ecosystem, but we want to know how the microbes in these different ecosystems affect the release of greenhouse gases from the soil," Cogger said.
"This research will improve our understanding of how carbon and nitrogen cycle between land, air and water in vegetable and row crop farming systems in the Pacific Northwest and Midwest," said Fortuna, an assistant professor of soil science at WSU and director of the project.
While a great deal is known about crop production and nitrogen fertilizers, she said, knowledge of the way soil microorganisms regulate the cycling of nutrients is limited.
"We need to learn how agronomic management practices alter the microbiology controlling these reactions," she said.
Video, guidelines, info to aid growers
The team plans to communicate the research results to growers via a video on climate change and soil microbiology.
The direct impact of the research will be a set of management practices for farmers, as well as information about the availability of nutrients in soils, Fortuna said.
The research has an additional potential bonus in that the team may be able to quantify a way to tell growers what their carbon footprints are, which growers could use in marketing.
Long-term study important
Research plots in Puyallup include a long-term organic farming experiment initiated in 2003. Because soil properties have been influenced by nine years of differing organic practices, the researchers expect to see differences in gas exchange from the soils over the next three years of their project.
Together with their colleague Ron Turco at Purdue University, who is studying the same thing in plots transitioning to organic status, they will not only measure emissions but also develop a series of "best practices" that farmers can use to minimize nutrient loss from their soils.
The researchers plan to measure the cycling of gases through the soil over several years because a single measurement is just a snapshot of the system at a given moment - not an accurate inventory of its behavior over the year-long cycle of growth, decay and renewal.
"Long-term data sets are few and far between in organic agriculture but are very much needed," said Fortuna.
Many factors affect soil, emissions
"Any time you are adding nutrients to a system and building them up, you need to be concerned about where the nutrients are going," Fortuna said.
In organic agriculture, nutrients are added via organic matter, including animal manure, residual plant matter after vegetables and grains are harvested, cover crops and compost. These materials are recycled by soil microorganisms, which releases the nutritional building blocks the next generation of plants needs to grow and thrive.
Soil is a complex, living system, so its fertility ebbs and flows with the rise and fall of temperature, the availability of moisture and other factors.
"All systems are leaky," Fortuna said. "Just because you have more organic inputs doesn't mean you are creating more greenhouse gases. There is probably a difference in the way the gases cycle.
"But you do need to have proper cropping and management systems in place to keep nutrients from escaping and becoming pollutants or contributors to greenhouse emissions," she said.