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?
Nature of science
Plantain is an example of why scientific research is so exciting. The science teams started with this question: Will herbs like plantain be suitable for summer feed? Along the way, new and interesting data caused them to pose new questions. The new puzzle pieces bring their own challenges as the research involves multiple processes at the animal level, plant level and soil level.
Dr Selai Letica from AgResearch investigates nitrous oxide emissions inhibitors.
Find out how greenhouse gases are measured:
The extra piece is an activity in which students assemble a tangram as a square and then reassemble the tangram incorporating an additional puzzle piece. The activity parallels the experiences of the scientists in this article and is an effective way to highlight aspects of the nature of science.
Soil moisture levels influence many of the microbial processes that happen underground. These activities aid student understanding about soil moisture:
DairyNZ has a section all about on plantain on it's website.
Ag Matters has actions, initiatives and case studies for reducing nitrous oxide emissions.
Dig deeper into plantain research with these articles:
- Plantain helping farmers to achieve environmental targets – DairyNZ Technical Series article
- Using alternative forage species to reduce emissions of the greenhouse gas nitrous oxide from cattle urine deposited onto soil – Science of the Total Environment article.
This resource has been produced with the support of DairyNZ.