Fertiliser giants Ballance Agri-Nutrients and Ravensdown are locked in a legal battle in the High Court over an attempt to patent the delivery method of a product which could play a vital role in making New Zealand farming more eco-friendly.

The case in the High Court at Auckland centres on Ballance's objection to Ravensdown plans to patent the delivery method of nitrification inhibitors. Ballance claims it will give Ravensdown a monopoly and hinder its own 18,000 farmer shareholders.

Ravensdown has been awarded pre-grant approval for the patent but Ballance has appealed in an attemptto stop them from gaining full approval.

Ravensdown general manager Richard Christie said the company wanted to patent the technology, the method of delivery, so that it could protect its intellectual property because no other company had developed such a method that was effective in reducing nitrate leaching and nitrous oxide emissions.

The technology, developed by Lincoln University, delivers the nitrification inhibitor by spraying or irrigating grazing pasture.

Christie said Ravensdown's method of delivering the nitrification inhibitor would improve pastures and therefore farmers' yields while providing greater sustainability to the industry.

Ravensdown says the method will also reduce potassium, calcium and magnesium leaching.

Ballance head of research and environment Warwick Catto said Ravensdown was trying to patent an invention that had been around for ages.

Catto said that if Ravensdown was given patent approval it would significantly benefit the company's bottom line "in the tens of millions".

"It will have a significant economic impact. It will reduce competition and prices increase when a monopoly is introduced."

Court documents said New Zealand's nitrous oxide emissions from animal excreta, mainly urine, account for 50 per cent of the country's nitrous oxide emissions, which make up 20 per cent of New Zealand's total greenhouse gas emissions.

Justice Patricia Courtney is expected to reserve her decision today when the trial is scheduled to finish.

The Intellectual Property Office of New Zealand says there are several benefits from gaining patent protection.

These include gaining exclusive rights to use and license your invention or product, allowing a business the right to take legal action against anyone who tries to use the product without consent and the fact that a patent could be enough to deter "would-be infringers".

The office said a patent gave a business a monopoly right to have exclusive use and control of an invention or product for up to 20 years.