Concerns over agriculture’s impact on global environmental change have prompted extensive research aimed at reducing greenhouse gas emissions and increasing carbon sequestration in row-crop, forest and livestock production systems, but a study underway at Auburn University is the first to zero in on one of the fastest-growing components of the nation’s agricultural sector: horticulture.

Several years into the project, Auburn horticulturalists, including professor Charles Gilliam and graduate research assistant Chris Marble, and federal researchers at the National Soil Dynamics Lab in Auburn are collecting data to determine what effects—not only negative but positive as well— ornamental horticulture has on impact, positive and negative, on climate change.

“What we’re doing is establishing baseline data on ornamental horticulture’s greenhouse gas emission and carbon storage levels, because right now, those are unknown,” Gilliam says. “But we’re also going to use that data to develop best management practices that will help producers operate more productively, profitably and sustainably.”

The researchers’ findings to date indicate that the size of containers nursery growers use and how they apply fertilizer both make a difference in the levels of carbon dioxide, methane and nitrous oxide released into the atmosphere.

Comparing trade-, 1-, 2- and 3-gallon containers that are standard in the nursery industry, they have found that greenhouse gas emissions increase right along with container size. But Marble says that doesn’t necessarily mean the industry should make a wholesale switch to the smaller sizes, Marble says.

“On a per-acre basis, emissions from a field of 3-gallon containers would be lower than from a field of 1-gallons, because there would be a lot more of them,” Marble says.

On the fertilization side, of three fertilizer placement practices—topdressing, incorporation into the potting media and dibbling—scientists say carbon dioxide emissions are lowest when the latter method is used, while nitrous oxide levels are highest when fertilizer is incorporated. Methane losses are negligible regardless of fertilization technique or container size.

Also as part of the project, researchers are investigating whether plant species and potting media affect carbon sequestration. Though pine bark is the standard substrate used in the industry, Gilliam and others at Auburn have developed two pine-bark alternatives in recent years—clean chip residual and whole-tree substrate. In the aspect of the study, the team is growing various common shrubs in the differing media, then planting the shrubs in a test field and monitoring carbon lost through soil respiration.

Early results indicate that the type of plant and the potting media it is grown in have significant effects on carbon sequestration in the landscape.

The study is funded by the USDA, Alabama Ag Experiment Station and Horticulture Research Institute.

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