#nitrogen fixing

Landscape Language

Thicket (noun) – a dense growth of shrubs

Mount Rainier is known for its old-growth forests, but along rivers or other area of disturbance you will likely find thickets of fast-growing trees and shrubs. A common species is red alder (Alnus rubra). In partnership with bacteria in their roots, red alders can remove nitrogen, an essential element for plant growth, from the air and "fix" it (store it) in their roots. This allows alders to colonize rocky riverbeds that have few soil nutrients and are unsuitable for most plants. Alders are fast growing and can quickly transition from thickets of shrubs to become trees up to 80 ft (25 m) tall.

IN THE UNITED STATES, more than 90 million acres of corn are planted every year. Corn uses more land than any other crop. It also uses a lot of fertilizer. By one estimate, 5.6 million tons of nitrogen are applied each year, along with nearly a million tons of nitrogen from manure.

Nitrogen is an essential nutrient for plants. While nitrogen makes up 78 percent of the atmosphere, only legume crops were known to have the ability to use it, through their association with bacteria.

“Legume crops like soybeans have nodules on their roots that harbor bacteria that can turn nitrogen in the air into a form the plant can use,” said Alan Bennett, distinguished professor of plant sciences at the University of California, Davis. “For cereal crops like corn, farmers must rely primarily on nitrogen fertilizers.”

Bennett is part of a multidisciplinary team of researchers from UC Davis, the University of Wisconsin–Madison, and Mars, Incorporated that has made a remarkable discovery: an indigenous variety of Mexican corn that can also fix nitrogen from the atmosphere, instead of requiring synthetic fertilizers.

The team’s findings were published Aug. 7 in the journal PLOS Biology.

If this trait can be bred into conventional varieties of corn, it could reduce the need for added fertilizer and increase yields in regions with poor soil. Corn that fixes nitrogen could also help farmers in developing countries that may not have access to fertilizer.

Myrica pensylvanica / Northern Bayberry

PLANT COMMUNITY: New England barrier beach

NATIVE REGION: Newfoundland to western New York, Maryland, North Carolina

MATURE SIZE: Height of 5-12′, spread 5-12′

HABITAT/GROWING CONDITIONS: Coastal regions; thrives in poor, sterile, sandy soil; extremely adaptable; fixes atmospheric nitrogen

ECO-INDICATOR: N/A

HARDINESS ZONE: 3-6

LEAF COLOR: Deep, lustrous green, leathery leaves

FLOWER COLOR: Yellowish green catkins

FRUIT COLOR: Grayish white fruit

VALUE FOR REHABILITATION OF DISTURBED SITES:  Bayberry is a natural selection for conservation plantings and for landscaping on coastal sands. Though not a legume, it does "fix" nitrogen and is an important constituent for revegetation efforts. Northern bayberry is used extensively throughout the Northeast to stabilize roadside banks and revegetate disturbed soil. It provides excellent stabilization and cover for sand dunes along the mid-Atlantic coastline.  On Sable Island, Nova Scotia, northern bayberry showed tolerance to experimental natural gas contamination.  On strip-mine spoil banks in southern Indiana that were amended with lime, 1- to 2-year-old transplanted northern bayberry seedlings had low survival rate at all lime levels. To raise the pH level of the acid mine spoils, lime was added at rates of 0, 12.5, 25, and 39 tonnes/ha. 

This technical note aims at encouraging farmers to take a closer look at the roots of legumes and become more familiar with the process of nitrogen fixation and its relevance for organic farming. The note provides some key information on biological nitrogen fixation and describes a simple method for examining nitrogen‐fixing root nodules.

Basically, dig up your legume (clover, beans, peas, etc.) just as it starts to flower. Cut open a few nodules on the roots; the plant is fixing nitrogen if the interior of the nodule is red. See photos and the interpretation of the findings chart in the article for more details.