Plantain research

Plantain has been in the spotlight as scientists and farmers investigate its usefulness as pasture feed and its potential environmental benefits.

Year-round pasture grazing

Aotearoa New Zealand is one of the few places in the world where cows can graze on pastures year round. The bulk of a dairy’s cow’s diet comes from a mix of perennial ryegrass and white clover. Ryegrass grows well for much of the year, but slows in summer and autumn as soil moisture levels drop. Forage plants with deeper roots such as plantain, lucerne and chicory can provide additional feed during the drier seasons.

Initial research aims

Plantain has been part of Aotearoa New Zealand pastures for a long time, but plant breeders have created new cultivars that are both more nutritious and palatable for dairy cows. The initial research focused on plantain’s effect on milk production and pasture management practices. Scientists found that dairy cows produced the same or increased amounts of milk. The trials also provided information on how to establish and maintain plantain as part of an existing sward or as a special-purpose crop.

Reduced nitrogen concentrations

Scientists also noted that plantain has additional properties of interest. Cows that consume plantain have reduced levels of nitrogen in their urine. This is due to lower nitrogen content in plantain (compared to other forage plants) and plantain’s possible diuretic properties – cows urinate more often so the nitrogen in urine patches is less concentrated.

Reducing nitrogen in urine patches is important. Industry group DairyNZ recommends using 50 kg N/ha of nitrogen fertiliser or less per single application to minimise nitrogen leaching to waterways. Urine patches can contain up to 700 kg/N/ha on average for a ryegrass and clover diet. This rate exceeds what the plants can use, so surplus nitrogen can leach below the root zone and enter groundwater and then surface water and create environmental issues.

Early results during trials show that using alternative forages like plantain can reduce the nitrogen concentration of urine by 25% and reduce nitrate leaching under urine patches by 30–60%.

Reducing greenhouse gas emissions

Microbial processes within soils such as denitrification convert nitrogen to other forms, including nitrous oxide (N₂O) – a long-lived greenhouse gas. Nitrous oxide accounts for around 12% of Aotearoa New Zealand’s greenhouse gas emissions. The country’s N₂O emissions rates have nearly doubled since 1990.

Scientists think that plantain might help to reduce N₂O emissions. Plantain reduces the amount of nitrogen entering the soil via urine patches so surplus nitrogen is reduced. A second area of research involves compounds the plants release into the soil. Scientists think these compounds are natural nitrification inhibitors – they reduce nitrogen mineralisation and nitrification. The research is ongoing.

Plantain may also help reduce another greenhouse gas – methane. Methane is produced in the rumen of cows and is released by burping. As with nitrous oxide emissions, early research results are tentative;

Moving from research sites to on-farm sites

Scientists carry out plantain research in controlled trials using careful experimental design. Some studies use lysimeters – devices that hold soil and are used to monitor soil interactions under controlled conditions. Research farms operated by DairyNZ and other agencies conduct trials with small herds of cows on small fenced paddocks. The farms operate in real-world conditions, but the trials are still controlled and carefully monitored. The next step is transferring the research to commercial farms that may have hundreds or thousands of animals. For on-farm programmes, the scientists work closely with farmers to co-develop the research projects.

The key part of agricultural science is ensuring the research is grounded in on-farm practice – that’s farm system science.

Kieran McCahon, Solutions and Development Specialist, DairyNZ

Many questions yet to answer

Even though researchers are building their knowledge about plantain, there are still a lot of questions:

• Does plantain have diuretic properties or do cows simply urinate more because plantain has a higher water content than other feeds?
• Do smaller urine patches created more often affect N₂O emissions?
• What biological mechanisms are responsible for reduced N₂O emissions?
• Does the plant structure affect N₂O emissions?
• Plantain does not affect milk production, but might there be changes to milk properties that impact manufacturing processes?
• Do seasonal patterns have an impact on the results?