A scientific review paper has torpedoed research underpinning a multimillion-dollar plantain project hoping to see the plant deployed as a nitrate busting solution for dairy farmers.
The New Zealand Journal of Agricultural Research has just published a scientific review of 15 years of plantain research in NZ. The report’s authors include Dr Tony Connor of Lincoln Genetics, a former manager of AgResearch’s forage science division. Another of the review authors includes Dr Jacqueline Rowarth who is also a DairyNZ director.
The review’s findings indicate aspects of plantain’s ability to absorb nitrates and to mitigate losses are suspect, and say there may be better alternative species worthy of further research work.
The review comes as the seven-year Sustainable Food and Fibre Futures (SFFF) plantain potency project passes the halfway mark, having spent $12.6 million of its $22m funding.
The project was launched in 2021 to help improve waterway quality and nitrate losses.
It comprises $9m of funding from the Ministry for Primary Industries and $10.47m in cash from DairyNZ, Fonterra and PGG Wrightson Seeds. The remaining $2.8 million is provided in kind.
Plantain has been promised to farmers as one of the most viable tools to help deliver improvements to nitrate levels, thanks in part to its claimed diluting effects on cow urine N levels, and its ability to reduce nitrate runoff through the soil profile.
DairyNZ’s own modelling has estimated it could reduce N losses by 15,000 tonnes a year, and provide savings of $1 billion between 2031 and 2040.
Three other areas the research is focusing on include plantain’s ability to partition more N into dung than urine, to directly prevent N leaching through soil, and to indirectly mitigate N breakdown in soils, thanks to particular metabolites in the grass.
Connor said other forages have not been adequately studied for their potential value as N-mitigation tools.
“Clearly plantain increases urination, we suspect that’s because it has a relatively high water content. But there are other forage with a higher water content that might perform as equally well as plantain.”
These include chicory and tetraploid ryes.
While helping lower N levels, plantain has also proven difficult for farmers to establish in their pasture swards and is consistently lower in yield than diploid ryegrasses.
In an extensive written response to Farmers Weekly, DairyNZ scientists defend the move to focus on plantain in the project.
They state the focus was because the weight of past evidence showed plantain had the greatest potential across all four mechanisms of N reduction, not only dilution.
“A key objective of the programme is to understand, confirm and quantify these mechanisms and their combined effect at paddock scale,” the response says.
“Once confirmed, this knowledge can be applied for modelling the effect of other high water content species such as chicory and paving the way for new research.”
They acknowledge challenges in maintaining plantain in established pasture.
“However, our network of partner farmers across NZ are demonstrating how they can make plantain work in their pasture systems.”
The review authors point to a lack of evidence plantain could partition more N into dung than urine.
DairyNZ maintains key research was omitted in the review, and says N levels in urine were lower for pastures with 30% and 45% plantain content.
The review has also challenged the long-held benchmark of dairy cow urine equating to 1000kg N a hectare, a factor driving the need to reduce cow urine concentration through plantain planting.
The authors say figures coming from United States data, and work by Dr Jacqueline Rowarth, instead places it much lower, at 240kgN/ha.
DairyNZ dismisses this as a red herring.
It says Rowarth’s work was sourced as a non-peer reviewed popular press article, with a narrow study range.
DairyNZ does, however, place the equivalent urine figure lower, at 600kgN/ha.
Issues around the use of lysimeter trials misreading or overstating N losses in plantain versus rye grass trails are also highlighted in the review.
DairyNZ has acknowledged the inconsistency of experimental results for testing soils under plantain pasture.
“This is a key focus for our programme, such that the effect can be understood, confirmed and quantified for a range of soils and climates.”
It also points to 26% lowered N levels after four years on the Massey trial farm on plantain pastures versus all rye, and at Lincoln where losses were 17% lower.
While the Lincoln data has not been published yet, the Massey data has, in Grass and Forage Science magazine.
DairyNZ says Rowarth’s DairyNZ directorship and apparent conflict reflects the nature of competition in a small country.
It notes she is also a director of Ravensdown, part owner of Cropmark, a competing seed company to PGGW Seeds, which is a project funder. One of the other report authors is Matt Deighton, Cropmark technical manager.
Cropmark also produces Oracle, a plantain variety.
With the mid-point of the project now here, DairyNZ says it is continually reviewing its project-based funding.
“We remain committed to the work we have done on plantain and finishing the programme.”
Andrew Miller, Fonterra’s GM for farm excellence, said there was no silver bullet to reducing N leaching, and that was why Fonterra has several research partnerships underway.
“We continue to support research that seeks to further understand the benefits of plantain at a farm scale, its impact on different New Zealand soils and its effects on dairy products and animal health.”
An MPI spokesperson confirmed the agency is aware of the review report.
They said all SFF Futures investments are subject to ongoing monitoring, and a scheduled independent mid-term review of the programme is underway now.
“This will help evaluate how the programme is progressing.”
The full research review can be viewed here.
In Focus Podcast | Red meat sector faces up to the challenge
Bryan attended the Red Meat Sector Conference this week and caught up with Meat Industry Association chair Nathan Guy, who outlined some of the structural shifts in the industry and gave his views on the big challenges sheep and beef farmers are facing at the moment.
