White clover will become an important environmental mitigation tool for farmers as they respond to new Government-imposed nitrogen caps, predicts seed company Germinal New Zealand.

"White clover, a natural nitrogen fixer, is a low-cost and practical resource for farmers. It can reduce the cost and environmental impact of artificial fertiliser," general manager Sarah Gard said.

"We expect white clover will play an increasingly important role in New Zealand's pastoral system as farmers seek to comply with the current regulatory landscape."

By July 2021 all pastoral farmers are required to reduce their synthetic nitrogen fertiliser use to come within a cap of 190kg per hectare, per year. The new policy is part of the Government's Action for Healthy Waterways package. Dairy farmers will also need to report annually to regional councils details of the weight of nitrogen they applied per hectare.

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The Government estimates 2000 dairy farmers - most in Canterbury and Southland - will need to reduce fertiliser use during the next 12 months to stay under the cap. But industry experts have challenged this figure, claiming up to 35 per cent of dairy farms might be affected.

Gard, who also manages two North Canterbury dairy farms with her husband Will, said that white clover had been overlooked by farmers in favour of high ryegrass levels to increase dry matter.

Germinal general manager Sarah Gard said. Photo / Supplied
Germinal general manager Sarah Gard said. Photo / Supplied

"A combination of lighter sowing rates for clover, increased use of nitrogen fertiliser, and soil nutrient deficiency means the majority of New Zealand farms have a clover percentage well below the optimum level of 30 per cent."

Germinal, also based in Ireland and the UK, has supplied the New Zealand market with innovative clovers and grasses for more than 15 years. A recent cost analysis by the company suggests Kiwi farmers can economically reduce their synthetic nitrogen use by switching to a high clover sowing rate.

"Our calculations show that the nitrogen inputs into a system with a nitrogen fertiliser application rate of 250kg per hectare per year, combined with a low clover sowing rate, would cost approximately $1580 per hectare during a five-year period," Gard said.

"By comparison, a system with a nitrogen application rate that meets the new 190kg cap and which has a higher clover sowing rate would have nitrogen costs closer to $1250 per hectare during the same five-year period.

"Clover will also have the ability to fix more nitrogen if there is less fertiliser applied, as it won't be suppressed by increased grass growth and subsequent competition for nutrients, light and water."

According to the Agronomy Society of NZ, nitrogen losses are lower from farm systems more reliant on clover than applied fertiliser, reducing a farm's environmental impact.

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A high clover sowing rate is not without risk, cautioned Gard.

"If the sowing rate is too high cattle can suffer from bloat. It can be mitigated, but it is something that farmers need to be mindful of. White clover also requires adequate attention - sowing rates, establishment periods and soil nutrient profiles all need to be considered."

Germinal NZ can draw on world-leading research through its research partnership with the Institute of Biological, Environmental and Rural Sciences in Wales, and apply it to New Zealand's conditions.

"The world is changing, with ever-increasing demands on New Zealand farmers," Gard said.

"It is important that we engage with farmers at the ground level to support a thriving and environmentally aware rural sector."