Nitrogen Fixing Bacteria

Design and InstallationGarden Caregarden TriviaIndoor plantsPlant Health CareUncategorized
Written By Peter Morris

typical soil bacterium

Nitrogen and Ammonia

Almost 80% of Earth’s atmosphere is nitrogen gas (N2) - unfortunately, it is unusable by most living things. All organisms use the ammonia (NH3) form of nitrogen to manufacture amino acids, proteins, nucleic acids, and other nitrogen-containing components necessary for life. 

clover !

Nitrogen Fixation

Biological nitrogen fixation is the process that changes inert N2 into biologically useful NH3. This occurs in blue-green algae (a bacterium), lichens, and free-living soil bacteria. These types of nitrogen fixation contribute significant quantities of NH3 to natural ecosystems but not to most crops. 

nodules on a soybean plant

All plants benefit from NFB when they bacteria die and release nitrogen to the environment, or when the bacteria live in close association with the plant.  Clover loves NFB ! 

In legumes and a few other plants, the bacteria live in small growths on the roots called nodules. Within these nodules, nitrogen fixation is done by the bacteria, and the NH3 they produce is absorbed by the plant. Nitrogen fixation by legumes is a partnership between a bacterium and a plant – a symbiosis. 

a field of red Alfalfa

Legume Nodules

Legume nitrogen fixation starts with the formation of a nodule by the rhizobia bacteria in the soil. It invades the root and multiply within its cortex cells. Within a week after infection, small nodules are visible with the naked eye. 

beans are in the Legume family

When young they are usually white or gray inside. As nodules mature they turn pink or reddish in color, indicating nitrogen fixation has started .

The pink or red color is caused by leghemoglobin (similar to hemoglobin in blood) that controls oxygen flow to the bacteria. On perennial legumes, such as alfalfa and clover, nodules are fingerlike in shape. They live from season to season. 

cross section of nodule and root tissue

On annual legumes, such as beans, peanuts, and soybeans, they are round and can reach the size of a large pea. These are however short-lived and will be replaced constantly during the growing season. In addition - once the plant begins feeding its seed – they lose their ability to fix nitrogen because the plant is sending sugars to the developing seed rather than the nodule.

Legume nodules that are no longer fixing nitrogen usually turn green and may actually be discarded by the plant. Beans will generally have fewer than 100 nodules per plant, soybeans will have several hundred per plant, and peanuts may have 1,000 or more nodules on a well-developed plant. 

tamarind pods with seeds - in the legume family

What are the benefits to the bacterium?

The fixed nitrogen is not free; the plant must contribute a significant amount of energy in the form of photosynthate (photosynthesis-derived sugars) and other nutritional factors for the bacteria. Its is also a safe haven to live in. 

Stress

Any stress that reduces plant activity will reduce nitrogen fixation - like temperature and water availability. Nutrition stress can be corrected with fertilizers. 

Nitrogen Return

Almost all of the fixed nitrogen goes directly into the plant. However, some nitrogen can be “leaked” or “transferred” into the soil and used by neighboring non-legume plants. Most of the nitrogen eventually returns to the soil for neighboring plants when vegetation of the legume dies and decomposes.

When the grain from a grain legume crop is harvested, little nitrogen is returned for the following crop. A perennial or forage legume crop only adds significant nitrogen for the following crop if the entire biomass is incorporated into the soil. 

Non legume inoculation

The legume symbiosis is very efficient and can supply all the nitrogen demands of the crop. It is therefore a prototype for engineering nitrogen fixation in the future.In addition to the legume symbiosis, nitrogen-fixing soil bacteria can be associated with cereal crops to meet some of their nitrogen requirements. This process is done by inoculating cereals with nitrogen fixing bacteria as biofertilizers. 

Bio fertilizers

There are many biofertilizer companies throughout the world that prepare inoculant formulations and sell these to farmers. However, in general this technology is neither as efficient nor robust as the legume symbiosis. All in all though - inoculants are far cheaper than nitrogen fertilizers, so provide cost savings for farmers.

Call us - we know our Legumes !  

PLANT SPECIALISTS

GREENING NEW YORK FOR OVER 53 YEARS !

Article written by our Staff Horticulturist, Peter B Morris, BSc, MSc, MBA

All photographs used with permission @SHUTTERSTOCK

Peter Morris

Peter was born and raised on a beautiful green island in the midst of a tropical rainforest. He was introduced into the world of plants at the age of six when his grandmother, an avid Spanish gardener herself, asked him to help her grow seeds for her pepper garden. He was hooked! By the time he was a teen, he had his own rose and orchid collection numbering in the hundreds. Botany was in his blood, and that is what he set out to study.

His passion brought him to NY in the late seventies to further his education. His tenacity allowed him to work full time at Plant Specialists while he completed a MS in Plant Biology. As a manager at the time he felt unsatisfied with his knowledge of business and business processes. Peter felt compelled to learn, so he then pursued and completed an MBA in Quality Management within a few short years.

Peter’s other passion is teaching. His natural ability is quickly consumed by our staff in all subjects in Botany, Horticulture, and Landscaping. He created an immense reference library of more than 3,500 plants providing an invaluable resource for our staff.

Peter’s breadth of knowledge and wisdom allows him to effectively diagnose the needs of plants. Sometimes just by walking into a garden he can create a prescription that fixes even the hardest issue. He is our Staff Botanist, Diagnostician, and all around Mentor. Recently, he has put his immense knowledge and skills into developing a new department that focuses on Plant Healthcare. As he puts it, “Magic through Science”. The PHC staff that surround him have avidly consumed his teachings. Substantially developing their own plant wisdom, many have taken on difficult plant health issues with spectacular results.

Plant Healthcare has been an instant success with customers! The proper treatment of insects and diseases including Organic methods has made pest control a necessity for every plant. Correcting hormonal imbalances caused by planting in containers or refurbishing soils leached of nutrients by irrigation systems are big challenges PHC has become quite comfortable addressing. The scientific approach to the complex demands of keeping plants healthy in our harsh city environment has made many a customer say WOW!

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Mycorrhiza and the Power of Garden Health