Using plantain in Rotorua

Dairy farmers in the Rotorua Lake catchment are working under Bay of Plenty Regional Council regulations to reduce nitrogen losses to Rotorua Lake. The goal is to reduce the nitrogen load from 755 tonnes per year to a sustainable 435 tonnes per year. For the 26 dairy farms in the catchment, this means:

• A collective reduction of 96 tonnes of nitrogen per year.
• An average 31% reduction in N leaching per farm by 2032/33.
• Step-down targets in 2022, 2027, and the final target in 2032/33.
• Individual farm Nitrogen Discharge Allocations (NDAs) modelled in OverseerFM

Meeting these targets will require most farms to combine multiple nitrogen leaching mitigations – a 'stacking' approach. Plantain is recognised by BOPRC as an effective, low-cost mitigation that can form the foundation of the stack.

Farm One - Richard and Amy Fowler

Farming on 100ha, milking 250 cows, running a system 3 farm.

Read more about Richard and Amy

Farm Three - Doug and Tina Dibley

Doug is a 5th generation dairy farmer, milking 400 cows on 130 ha on Pumice soils.

Farm Five - Waerenga

Waerenga is a Māori owned farm milking around 1000 cows on 354 ha on Pumice soils on the north-east shore of the Rotorua Lake.

How plantain reduces nitrogen leaching

Trials conducted through the Plantain Potency and Practice Programme show that plantain is a low cost, moderate impact tool for reducing nitrate leaching. Plantain reduces nitrogen leaching in these ways:

• Dilutes urine → more water intake, lower nitrogen concentration.
• Reduces nitrogen excreted via urine → more goes into milk/faeces.
• Reduces drainage → less water movement, less nitrate loss.
• Changes nitrogen cycling → less nitrogen lost as nitrate (exact mechanisms still under investigation).

What Rotorua farmers are achieving

From 2022-2025, DairyNZ worked with five partner dairy farms in the Rotorua Lake catchment as part of the Plantain Potency and Practice Programme. These farms, located on the Mamaku Plateau on pumice and podzol soils at 400-600m elevation, provide practical evidence of what's achievable in local conditions. Through annual broadcasting of Ecotain plantain seed, partner farms achieved:

• 15-20% plantain (as a percentage of pasture dry matter) across whole farms on well-drained pumice soils.
• 30-40% plantain in paddocks where plantain was drilled with new pasture following crops.

What influences plantain establishment

Partner farms showed several factors affect plantain establishment success.

Establishment method: Broadcasting achieved 15-20% plantain. Drilling plantain with new pasture following crops achieved 30-65% in those paddocks.

Annual application: Farms that broadcast 2kg/ha annually maintained plantain levels. Some evidence suggests persistence for 2-3 years on certain farms.

Steep areas: Very steep areas where seed spreading is difficult had lower plantain content. Drone spreading was trialled, but results were variable.

Soil drainage: Farm 4, with podzol soils and an impermeable tephra layer, achieved lower plantain levels (12%) despite similar seeding rates. Low-lying areas prone to waterlogging and pugging had particularly poor establishment while undulating areas achieved similar levels to the other partner farms. An area grazed by dry stock with annual Poa grass burden also achieved lower establishment.

How to establish plantain in Rotorua

Annual broadcasting

For most Rotorua farms, annual broadcasting of plantain seed is the most practical and cost-effective approach to achieve 15-20% plantain across the whole farm. What works:

• Timing: Spring (October-November) with phosphorus fertiliser application. Some success has also been achieved in autumn.
• Method: Spread seed with fertiliser from a fertiliser truck or tow-behind spreader.
• Coverage: Broadcast across the whole farm including support blocks.
• Seed rate: 3-4 kg/ha bare seed equivalent in year one, then maintain at 2 kg/ha. Double the rate for Prillcote seed which will provide a more even spread.

Include plantain in new pastures

When renewing pastures, include plantain in the seed mix to achieve higher plantain content in those paddocks.

• Seed rate: 3-4 kg/ha plantain with 16-21 kg/ha perennial ryegrass and 3-5 kg/ha white clover.
• Result: 25-50% plantain in the first 1-2 years. Maintain with broadcasting as above.
• Control broadleaf weeds while they are small with post-emergent herbicides on label for use in plantain and clover. These sprays are less effective for mature broadleaf weeds.

Grazing and management

No changes to normal grazing management are needed when plantain is part of a mixed sward.

• Continue rotational grazing to achieve 2-3 leaf stage on ryegrass.
• Maintain normal target covers and residuals.
• Spot spray to control broadleaf weeds, or in heavily infested paddocks, spray out and re-establish plantain by broadcasting.

Nitrogen leaching reduction

When modelled in OverseerFM, incorporating 20% plantain into pastures reduced nitrogen leaching by 8-14% across the partner farms, with an average reduction of 11%.

Note: The actual benefit may be greater due to additional soil mechanisms not yet captured in the OverseerFM model. Preliminary results from the Lincoln Plantain Potency and Practice farmlet trial shows 26% N leaching reduction from swards with average 17% plantain.

Plantain's value in a mitigation stack

Most Rotorua farms will need to combine multiple mitigations to meet their 2032 NDA. Modelling shows that including plantain in the stack makes meeting targets more profitable than without it.

Result: Using plantain as part of the mitigation stack was 4.7% more profitable than meeting the same NDA target without plantain.

Result: Using plantain as part of the mitigation stack was 7.5% more profitable than meeting the same NDA target without plantain.

(Modelling based on 2021-22 season data with $9.30/kg MS milk price)

Key finding: Using plantain as part of a mitigation stack resulted in 4.7-7.5% higher profit compared to meeting the same NDA targets without plantain. This is because plantain's low-cost N reduction means you need fewer of the more expensive mitigations like removing all N fertiliser or reducing stocking rate.

Catchment-scale impact

If all 26 dairy farms in the catchment achieved 20% plantain, modelling estimates this would reduce nitrogen entering Lake Rotorua by 35 tonnes per year – approximately one-third of the dairy sector's 96-tonne reduction target. Cost savings from using plantain in place of other mitigations, such as reduced inputs, lower stocking rates and/or earlier culling, are estimated at $500,000 per year if all 26 dairy farms in the catchment implemented plantain at 20%.

Case study: High profit with low N leaching

One partner farm demonstrates that high profitability and low N leaching are achievable together. Key features of this farm system:

• Low-cost structure: Operating expenses 67% of the district benchmark.
• Strategic N fertiliser use: Reduced from 40 kg/ha to zero over five years, using tactical applications only when needed.
• Low imported supplement: 0.4 t DM/ha compared to benchmark of 2.1 t DM/ha.
• Plantain: 21% across the farm through annual broadcasting.
• High clover: 17% clover content (higher than other farms due to low N use).

Result: N leaching 25% below catchment average (40 vs 53 kg N/ha) while operating profit was 142-159% of the district benchmark.

Thank you to Bay of Plenty Regional Council, and our Rotorua partner farmers Richard and Amy Fowler, Steve and Paula Holdem, Claire and David Beuth, Doug and Susan Dibley, and Waerenga.