Farmers Weekly writer Richard Rennie has drawn attention to a scientific review which raises questions about the investment in research on plantain’s ability to reduce nitrate levels. The review suggests alternative species may be better placed for farmers to deploy.
The plantain project aims to have plantain deployed as a nitrate busting solution for dairy farmers.
The New Zealand Journal of Agricultural Research has just published the 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, and Dr Jacqueline Rowarth, who is also a DairyNZ director.
Mr Rennie writes:
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.
Mr Rennie notes that 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.
The research also is focused on 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.
But Dr Connor says 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 proven difficult for farmers to establish in their pasture swards and is consistently lower in yield than diploid ryegrasses.
The Farmers Weekly report acknowledges that DairyNZ scientists provided it with an extensive written response, in which they 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 counter by saying key research was omitted in the review, and that N levels in urine were lower for pastures with 30% and 45% plantain content.
The review 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, places it much lower, at 240kgN/ha.
DairyNZ has dismissed this as a red herring and says Dr Rowarth’s work was sourced as a non-peer reviewed popular press article, with a narrow study range.
DairyNZ places the equivalent urine figure at 600kgN/ha.
The Farmers Weekly report can be found here.
The full research review can be viewed here.
Source: Farmers Weekly
