Nitrogen fixing clovers: A sustainable fertiliser alternative

Kiwi farmers continue to face challenges due to extreme weather caused by climate change and have been impacted by rising fertiliser prices. In response, farmers are increasingly using nitrogen fixing clovers as alternative sources of nitrogen fertilisers to improve self-sufficiency in the face of these challenges.

This guide will address the key questions around clover’s nitrogen fixing properties.

What is nitrogen fixation in clover and why is it important for farmers?

Nitrogen fixation is a biological process where atmospheric N2 is converted into forms that can be used by the plant as a natural, cost-effective alternative to chemical fertilisers. The process is specific to legumes, a select group of plants including clover. Clover fixed nitrogen can also benefit companion grasses through transfer in soil and through animal returns.

How does clover fix nitrogen in soil?

Nitrogen fixation is performed by symbiotic rhizobia bacteria. These bacteria colonise specialised structures called root nodules. The clover plant supplies carbohydrates to the rhizobia that are then used to convert atmospheric nitrogen into a form utilised by the plant.

DoubleRoot AberLasting clover roots fixing nitrogen in soil

How much nitrogen does clover fix?

When managed carefully to maintain clover content 25-30% in paddocks, nitrogen fixation rates can average 150 kg N/ha/year. Once this is achieved, nitrogen fertiliser application rates can be significantly reduced with clover/grass paddocks supplied with as little as 100 kg N/ha. This is as productive as, or more productive than, grass monocultures at 250 kg N/ha.

Why nitrogen is required for grass and clover growth

Nitrogen, along with phosphorus and potassium, is an essential macronutrient of plants. It is also a key component of proteins, nucleotides and plays a major role in the metabolism.

Growing crops depletes the soil of nitrogen, which then needs to be replaced for the soil to remain fertile. Several options are open to farmers, such as the application of industrially produced fertilisers.

But this has a large carbon footprint, with 3.3 tonnes of CO² equivalents being produced in the EU  and 9-11 tonnes in China for each tonne of N fertiliser using even the most efficient processes. The CO² emitted in the manufacturing process is derived from fossil fuels and has a major impact on the environment.

Clover can be a sustainable substitute for nitrogen fertiliser

While nitrogen fertiliser has been used successfully by farmers to improve productivity and profit, its case has weakened in recent years. The recognition of the environmental cost of fertiliser production and transport, along with soaring nitrogen fertiliser costs has exposed the detrimental impact of using nitrogen fertiliser.

Nitrous oxide emissions

Along with the environmental cost of production and transportation, applying nitrogen fertilisers is associated with nitrous oxide emissions.

N2O is a highly potent greenhouse gas with 265 times the atmospheric warming potential of CO² on a per-molecule basis. Nitrous oxide is also the single most important ozone-depleting emitted gas. Faced with this challenge, increasing numbers of Kiwi farmers are using clover as a natural and sustainable nitrogen supply.

Ammonia emissions

Also concerning is ammonia (NH3), an air pollutant known to damage biodiversity, ecosystem resilience and human health.

Ammonia emissions are generated by many common farming practices, including housing livestock, storing and spreading manure and slurries, and the application of nitrogen fertiliser. Reducing ammonia emissions in New Zealand farming is also vital.

The ammonia used in our primary industries is produced by the Haber-Bosch process, which utilises fossil natural gas generating 2.6 metric tonnes of lifecycle greenhouse gas emissions per metric tonne of ammonia produced.

Ammonia’s production accounts for approximately 2% of global fossil energy usage, generating over 420 million tonnes of CO² annually. Increasing the use of nitrogen fixing clovers will help us use fewer greenhouse gas emissions in the production and application of inorganic nitrogen fertiliser.

How to choose the best clover for nitrogen fixing?

Both red and white clover can provide you with nitrogen fixation and your choice should be made based on the needs of your farming system.

Grazing option: White clover and perennial ryegrass

White clover and perennial ryegrass are suitable for grazing. Compared with red clover, white is slightly higher in protein content.

Perennial ryegrass and white clover

But red's protein is naturally more stable than white clover protein due to the action of the enzyme polyphenol oxidase (PPO), which occurs naturally in the leaves of red clover.

This offers a degree of protection from degradation in the rumen and in the ensiling process and can be viewed as a natural bypass protein.

Grass and red clover silage option

Perennial ryegrass and red clover can be combined to produce silage as another feed source.

Perennial ryegrass and red clover silage

While white clover contains slightly more protein, red can have two-to-three times as much dry matter (DM) content. The combination of perennial ryegrass and red clover is well-suited when it comes to timing and planning silage cuts.

AberLasting: A DoubleRoot hybrid clover

AberLasting is a DoubleRoot hybrid clover providing a high-quality, homegrown protein option helping farmers work towards net zero goals.

Compared to conventional white clovers, this world-first, exclusive hybrid of Caucasian and white clovers is more resilient when facing temperature and drought extremes caused by climate change.

DoubleRoot varieties such as AberLasting grow like traditional white clovers in the first year. Individual plants form a deep taproot that dies off, with stolons starting to grow by spreading out and forming new plantlets along the stolons on the top of the soil.

AberLasting is a DoubleRoot hybrid clover variety

After the first year, a network of rhizomes is created from underground stems, which also form new plantlets. With DoubleRoot varieties like AberLasting, farmers can have a clover that produces stolons and rhizomes.

This ensures DoubleRoot clovers can survive periods of drought that would eliminate white clovers. As a result, this hybrid clover can survive exposure to severe cold by withstanding harsh overnight temperatures of down to -30°C.

DoubleRoot will also tolerate much harder grazing and mechanical damage. This gives Kiwi farmers a much more resilient clover that will continue to protect and regenerate soil while enduring extreme conditions.

How to grow clover and use it in your farming system

Different techniques can be used for the establishment of red and white clover, and the same goes for the management of these forage crops. Check out our clover management guides for more information.

Ask for Germinal's climate smart grasses and clovers

You can ask for Germinal's climate smart grasses and clover at your local seed merchant or talk to our experts if you have any questions.

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