Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Nitrogen leaching breakthrough

It’s hard for farmers to turn a profit at the best of times, let alone while reducing their nitrogen footprint. But a study by Landcare Research has found farmers can achieve both.

Landcare Research has proven the age-old farming practice of growing lucerne can help farmers like Mike and Sharon Barton meet water quality compliance rules, which they previously viewed as a handbrake on their business.

The Barton’s farm is within the vicinity of Lake Taupō, New Zealand’s largest lake. Due to concerns about the health of the lake, the Waikato Regional Council set nitrogen discharge caps on farms in the Taupō catchment.

The Lake Taupō Protection Trust also facilitated permanent change in land use, including conversion to forestry, in order reduce the amount of nitrogen entering the lake by 20 per cent (approximately 170 tonnes).

However, the trust has also turned to science to find long-term ways farmers can reduce their nitrogen footprint. Findings from a five-year-study by Landcare Research have shown the answer was right under everyone’s noses – cut and carry lucerne.


Dr Malcolm McLeod, a soil scientist at Landcare Research, found nitrogen leaching from cut and carry lucerne - where the leafy high protein forage is harvested and baled into hay or silage - is 5kg per hectare per year. This is significantly less than the 19kg per hectare per year set by the Waikato Regional Council and than previous estimates of up to 26kg per hectare per year.

“The actual leaching is quite low. It’s very similar to cut and carry pasture,” Dr McLeod said.

This gives farmers a lot more “leeway” as they may only have a discharge allowance between 12 and 20kg of nitrogen per hectare per year.

Each farm has a different nitrogen discharge allowance. A farm’s NDA was determined by the year it had the highest leaching during the benchmark period of July 2001 and June 2005.

He said the findings were great news for farmers.

“Costs are going up for farmers and the nitrogen cap limits how much production they can do, but lucerne provides a potential alternative. Now they know how much it’s leaching they can put in quite big areas and increase production,” Dr McLeod said.

The finding has been passed on to the Overseer committee.

“It’s another tool in the tool box to try and keep the lake in good condition,” he said.

Another added benefit for the lake was that lucerne used nitrogen from the air so did not require any nitrogen fertiliser, Dr McLeod said.

The data for the study was collected from 12 barrel lysimeters installed on the Barton’s 142 hectare beef farm in Tihoi.

Mike Barton said they supported the research because up until that point nothing had shown how farmers operating under a nitrogen cap could increase their stocking rate or profitability.

Win for farmers

The research was the “first significant win” for farmers, he said.

“It’s probably the first real breakthrough we’ve had in the nitrate issue since this process began back in 2000.”

It provides hope for farmers who have been struggling for some time, he said.

“The real price for food producers has gone down over the last 60 years. Our response has been to increase our carrying capacity – increasing production per hectare - but nitrogen caps denied farmers the ability to intensify.”

Uptake already

Cut and carry lucerne provided an economically viable alternative and some farmers were already taking it, Mike said.

“Quite a few dairy farmers outside the Taupō catchment, aware of the research, have brought land in the catchment and are growing lucerne and exporting it outside the catchment.”

“That land was also less expensive land so it made it worthwhile from a financial point of view for farmers outside to buy it but still be able to use it and transport it out,” Sharon said.

Mike said lucerne allowed farmers to double their dry-matter production without increasing nitrogen leaching.

“Control lysimeters are growing between 9000 and 10,000kg of dry matter in a year. The lucerne is growing 20 to 25 tonnes of dry matter, so more than twice what the grass is growing and we’re leaching the same. That gives you a clue of how important it is.

“If I can grow twice as much dry matter and still stay within my leaching limit that allows me to either finish cattle more quickly or finish them to higher weights. Either way it’s a win for us.”

National importance

Mike said the research was of value to farmers across the country as other regions, including Canterbury and the Manawatu, followed suit setting nitrogen discharge caps.

“This sort of research can have application on any other free draining soils. It’s been carried out on pumice soils but there is a cross over, so any other catchments facing similar nutrient capping challenges this research has application for them.”

Lake Taupō Protection Trust chairman Clayton Stent agreed.

“That lucerne research is relevant to any farmer across New Zealand. Any gains that can be made in certainty, which this particular research has done, assists our local farmers but that research is available to any farmer when it comes to nitrogen discussions. It’s a very valuable piece of research not just locally, it will have national recognition.”

Preserving an icon

While the research is of help to farmers struggling with nitrogen discharge caps the key benefit is to Lake Taupō, Stent said.

“The obvious benefits of the project are the health of the lake, which was the whole driver for this. Ultimately, what it’s about is stopping the nitrogen growing plants in the lake which choke it,” he said.

And it’s already appearing to work.

“It’s a 30 to 40 year outcome before we know truly whether it’s worked, but initial response from the science is that it has started working, there’s been a bit of an arresting.”

He said the project proved how a huge challenge could be overcome by the community coming together and working collaboratively.

Grazed pasture

The next stage of the project would look at what impact urinary nitrogen from livestock grazing on lucerne pastures had on nitrogen leaching.

Work would soon begin installing new lysimeters on the Barton’s property. Urine patches would be used to simulate the areas being grazed. This next phase would run for four to five years.

Mike said if the findings were the same as the cut and carry project it would be a “huge breakthrough”.

The research was funded by the Lake Taupō Protection Trust and the Ministry for Primary Industries Sustainable Farming Fund.


You may also like


Please note - these comments are moderated

Add a comment

*Comments are required for submission.