N fixation diagram by Nefronus

Some symbiotic or free-living microorganisms can fix inert di-nitrogen (N) from the air into reactive organic nitrogenous compounds.  Most biological N fixation (BNF) in farming systems occurs in the root nodules of legumes where rhizobium bacteria take photosynthates from the plant in exchange for fixing atmospheric N and returning ammonium or amides which the plant uses to form amino acids, proteins, etc.   Plants need more N than any other nutrient and N commonly limits plant growth in many ecosystems. 

Crop plants that fix most or (often) all of their N requirements by BNF include peas, beans (both Vicia & Phaseolus), clovers, lucerne (alfalfa), and lupins.  Amounts of N fixed often exceed the legume's needs so rotations, companion crops and crop mixtures with non-leguminous crops are commonly employed within cropping systems. 

Rhizobium species are specific to legume species, and may not be native in some soils, so BNF by some legumes may require their inoculation with suitable Rhizobium strains. 

Research over many years has sought to introduce BNF into non-leguminous crop species, thereby overcoming or reducing their need for fertiliser N.  Some BNF supports commercial sugar cane cropping, but the benefits of BNF to other crops remain minimal.    

Related Organisations

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Connected Content

Pulse Crops

Pulses are leguminous crops harvested for dry protein-rich seed, with peas (pisum sativum) and beans (vicia faba) being the major crops in the UK.

NCSPulse PEP
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Nitrogen is required annually by most crops (except pulses) to achieve yield and quality. Judging how much N to apply is a key part of nutrient management.

NCSPulse PEP
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The intricate web of relationships between physical, chemical and biological soil components underpins crop and livestock health and productivity.

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Legume is the commonly used name for the family of flowering plants, Fabaceae. Any plant in the Fabaceae family that has leaves, stems and pods are referred to as a Legume.

The role of Regenerative Agriculture in food production systems

Presentation by Ken Giller at IFS in 2021. See a preview in the video below, see the fu

Food & Farming Systems

This topic refers to the whole food supply chain, from farm fork, and all the products and services that contribute to food production.

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Field beans (vicia faba) are a widely grown break crop across the UK on around 170,000 ha. 

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A forum for technical information about all aspects of fertilisers and crop nutrition.

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The John Innes Centre is an independent, international centre of excellence in plant science, genetics and microbiology

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Living Mulch

Interest is growing in using legumes like lucerne or clover as a permanent understory to cereal crops to provide nitrogen through the season.

Clover

Clover is commonly used as a cover crop, forage crop, and soil improvement tool. 

Trial report: Utrisha N on winter oats

As part of the AICC Crop Nutrition Club 2022, this on-farm winter oats trial tested the effects of applying Utrisha N. The trial was facilitated by a local AICC advisor, with support and Agronomics yield map analysis from ADAS.

Trial report: Utrisha N on winter wheat

As part of the AICC Crop Nutrition Club 2022, this on-farm winter wheat trial tested the effects of applying Utrisha N at two contrasting N rates. The trial was facilitated by a local AICC advisor, with support and Agronomics yield map analysis from ADAS.

University of Warwick

Warwick Crop Centre is a national centre of excellence for research on fresh produce. We provide post-graduate training and specialise in research projects promoting sustainable agriculture, horticulture and food security.

PGRO trial - Nitrogen Use Efficiency and rotational impact of pulses

The trial will evaluate the long-term effects of pulses in an arable rotation, particularly the effect on available N to following crops. Objectives are: To evaluate the effects of winter beans, winter bean/ winter wheat intercrop and spring beans on soil nitrogen supply annually over 5 years. To evaluate the effects of species and species mixtures on GHG emissions. To evaluate impacts on soil structure and health resulting from cropping differences.

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Nitrogen Fixation

Nitrogen (N) is not a scarce element on earth but the most abundant forms (N2 gas in the atmosphere and N fixed in the earth’s crust and sediments) are not directly available for plants.

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Why Hasn’t Biological Nitrogen Fixation Fixed Nitrogen Scarcity in the World?

Really insightful piece from Andrew McGuire of Washington State University:

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