Harvesting free nitrogen

Canterbury arable farmer David Birkett describes how he uses legume cash crops to fix and store soil nitrogen which can then be used by the next cereal crop. While not mentioned in the video, David also benefits from the nitrogen fixed by legumes that volunteer in his earlier sown cover crops.

Video description: David Birkett talks about his use of legume cash crops to fix and store soil nitrogen.

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David Birkett: Budgeting for nitrogen capture

• David uses a mass budget that he has developed over the years to calculate how much nitrogen is fixed by his legume crops.

• On his soils, he estimates 150kgN/ha is fixed each year by a white clover crop, and around 130kgN/ha from a pea crop (when residues are retained).

• This translates to around $450/ha of free nitrogen supplied to the following cereal crop (at 2021 prices).

• In the last three year David has been able to reduce total fertiliser inputs to the farm by around 20%, coming off an already low base.

“The more you can give back to the soil, the more it gives back to you.”

David Birkett, Canterbury arable farmer

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