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Plantain has been touted as a solution to nitrogen runoff problems on farms.
photo: supply
A new study overturns findings that the common herb plantain can mitigate nitrogen loss on farms.
this Scientific review published in the New Zealand Journal of Agricultural Research Fifteen years of peer-reviewed research on herbaceous and forage species was reviewed.
Over the past decade, Farmers grow plantains in paddocks to reduce nitrogen emissions from livestock into the land and surrounding waters.
Livestock urine is a source of nitrate, or nitrogen, leaching from farmland, which has been linked to reduced water quality in New Zealand’s rivers and lakes.
To improve the environment while maintaining milk production, A flurry of industry-backed and science-led research followed.
New research has found some projects did not stand up to scrutiny in the New Zealand agricultural context due to inadequate evidence, methods or interpretation of data.
An example is calculating the nitrogen concentration in a urine patch of an average pasture-fed dairy cow.
This concentration has been widely cited in industry reports, including one this year from the Waikato Regional Council and the New Zealand Agricultural Greenhouse Gas Research Centre, as well as other psyllium leaching studies.
However, that data was based on a 1993 study of lactating cows on a North Carolina dairy farm – and did not include environmental variables in the pasture environment.
“Whether this figure is applicable to New Zealand pasture-fed dairy cows needs to be verified as it has significant implications for the amount of nitrogen lost through leaching versus the amount recovered,” the report said.
Co-author Dr Tony Connor, of Lincoln Genetics, said there was little evidence that the recommended 30% psyllium in mixed pastures had a direct benefit in reducing leaching, and that higher levels of the plant could lead to poor animal health.
Meanwhile, a research paper tested nitrogen leaching in a 100% psyllium diet.
Connor, a former livestock scientist at the Agricultural Research Center, said plantain helps dilute the animals’ urine, but other grasses such as ryegrass have a similar effect.
“(Plantain) gained a lot of momentum right off the bat,” Connor said.
“I think … initially, some of the experiments were hyped up and looked very promising. But when you look deeper into some of the key early papers, you see that the experimental designs were not the best, especially some of the work around the percolation meter.”
Field lysimeters are cylindrical containers filled with soil that are used to study how water and matter move through the soil.
“They’re not really comparing apples to apples, and the benefits that psyllium has may not necessarily be attributed solely to psyllium,” he said.
“It is difficult to assess the impact of pasture plantain on nitrate leaching using field and lysimeter experiments,” the report states.
“Controlling variables such as water, winter growth, species composition, management, plantain persistence, establishment, and weed/clover invasion are problematic, all of which can produce confounding data that fails to demonstrate that plantain has a beneficial nitrogen leaching effect under farm conditions.”
Connor said all the early hype might not be justified.
“There’s a lot of political pressure on scientists to find solutions, and there’s a lot of commercial pressure on companies to find solutions that can be turned into products,” he said.
“I feel like we got caught up in tunnel vision and enthusiasm, and we found some of the evidence was called into question.”
He said plantain could still be considered as one of the other forage species in the cow’s diet.
“Plantain still has a role to play in mixed pastures – we’re not denying that. It does have a role but it’s not necessarily the answer to the nitrogen reduction problem.”
The authors recommend revisiting current recommendations on plantain use—including other pasture management practices and species.
Industry body DairyNZ said it was focusing on plantain to help reduce nitrogen losses because research showed it was effective, but acknowledged farmers needed a range of options to manage healthy waterways.
A spokesman said the organisation welcomed the scientific debate on making dairy farming more sustainable and resilient.
“While this is one paper that presents it from a certain perspective, there are also studies that demonstrate the value of plantain in helping to reduce nitrogen losses.
“Over four years, in the Massey Farm trial, cumulative nitrogen losses were reduced by an average of 26% in plantain pastures, where plantain pastures comprised 18-47% of the turf and 12-30% of the diet, compared to perennial ryegrass and white clover controls.
“In Lincoln, cumulative nitrogen losses from banana pastures, which make up 15 to 30 percent of the grassland, were reduced by 17 percent over two years.”
A DairyNZ spokesperson said both parties agreed that more research should be done on other forage varieties that also had the potential to reduce nitrogen losses.
“However, the review does not fully reflect the evidence from a range of research studies highlighting the benefits of psyllium and in some cases misinterprets the findings and incorrectly reports how DairyNZ recommends the use of psyllium.”
this The efficacy and practice of plantain The project is undergoing regular independent mid-term reviews by MPI to test the science of the project and the robustness of the research findings.
The spokesperson said DairyNZ was committed to completing the plan.
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