Rhizobium and Nitrogen Fixation

New Zealand Agriculture

Biological nitrogen fixation is of particular importance to New Zealand agriculture, providing 1 million tonnes of nitrogen annually. Compared to the 26,373 tonnes of nitrogenous fertiliser used by New Zealand farmers this is more than 97% our annual requirements. Although this process is free, self-sustaining and non-polluting, it does not necessarily operate with optimum efficiency.

Partners for Life

Nitrogen fixation is the process by which atmospheric nitrogen gas is made available for incorporation into organic compounds. Only certain bacteria are capable of carrying out this process, the genus Rhizobium being the most common. Members of this genus are Gram negative aerobic rods that occur free-living in soil or as micro-symbionts in root nodules of leguminous plants.

World-wide Impact

Rhizobia in root nodules are estimated to carry out 50-70% of the world biological nitrogen fixation, reducing approximately 20 million tonnes of atmospheric nitrogen to ammonia. It has been demonstrated that one difficulty with relying on natural populations of Rhizobium is that they can transfer nitrogen fixation genes to other soil bacteria such as Caulobacter. These bacteria then compete for host plants but may not in fact be able to fix nitrogen at all.

School Experiments

The process of biological nitrogen fixation may be ideal for a medium to long term study with a senior class. There are opportunities to demonstrate some of the microbiology ideas and techniques in the Level 1 NCEA Science curriculum. Rhizobium is also an ideal organism to demonstrate gene transfer with Year 12 and Year 13 classes.

  1. Read some of the early ground-breaking research carried out in New Zealand
  2. Try these other investigations looking at microbes in the environment

We have carried out some of this work with the assistance of the L.A. Alexander Trust.

Nitrogen fixing bacteria (Rhizobium) inhabit root nodules on clover

Root nodules on White Clover...a symbiotic relationship between plants and bacteria


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