Opinion: Continuing fear over synthetic nitrogen fertiliser means scientists have to keep trying to dispel the alarm and reassure society, Dr Jacqueline Rowarth writes.
Advances in science are made through unbiased observation and systematic experimentation.
The scientific process is one of constant testing and re-evaluation. And when the evidence changes, perhaps due to further experiments and trials under extended factors, scientists amend their interpretations.
It is this test and rethink that has enabled progress over decades of research.
In contrast, activists appear to hold their views, trotting out the same lines and creating alarm.
The frustration for scientists is that people are unnecessarily frightened and taxpayer money is wasted in pursuing a perceived concern that has already been shown to be true or false.
Greenpeace wants the Government to phase out synthetic nitrogen fertiliser, yet again stating that there is a growing body of evidence that high nitrate in drinking water is linked to bowel cancer and premature births.
This puts the scientists in the position, yet again, of trying to dispel the alarm and reassure society: the World Health Organisation monitors the research and continues to support 11.3 mg/litre N as nitrate in drinking water as being safe.
ESR's 2021 report concluded that consumers in New Zealand are not at risk – and that nitrate in drinking water is a very small proportion of dietary nitrate.
Nitrate is the chemical in beetroot and kale that makes these vegetables, and many others, good for heart health. Google "superfoods" and they will appear.
Some internet sources are more reliable than others, but in general, the links are positive.
The authors (mostly Australian) of a large-scale Danish study concluded that "consumption of at least 60 mg/day (approximately 1 cup of green leafy vegetables) may mitigate the risk of cardiovascular disease".
They did acknowledge that association wasn't the same as cause but explained that end-products of dietary inorganic nitrate metabolism, nitrate and nitrite, are recycled back into the saliva.
As inorganic nitrate plays a key role in heart health, the recycling aspect indicated the possibility that dietary nitrate could be an important source of inorganic nitrate benefitting cardiovascular health. Their finding suggests that it is.
(They also commented that they were unable to investigate potential interactions with known inhibitors of the recycling pathway such as antibacterial mouthwash – an interesting note for those who like the taste…).
Because nitrate is metabolised in the mouth there is no plausible mechanism for it reaching the bowel or placenta to cause colorectal cancer or preterm babies.
This should be reassuring and allow research money to be focused on areas where progress might be made. Education on eating more fruit and vegetables has certainly been a push in Denmark.
The issues around pre-term have been associated with lower socio-economic groups globally; again, education will help.
The second confusion is the suggestion that regenerative agriculture and the use of natural nitrogen-fixers such as clover and legumes will make a difference.
The leaching of nitrogen into waterways depends on quantity of nitrogen in the soil, not the source.
Research at Ruakura in the 1990s showed that a ryegrass-clover paddock fixing 147 kg of nitrogen per hectare leached the same amount of N as a ryegrass pasture fertilised with 147 kg N per hectare as urea.
Listen to Jamie Mackay interview Dr Jacqueline Rowarth on The Country below:
The research also showed that the results year-to-year were highly variable and influenced by grass growth and rainfall.
Lower growth and higher rain resulted in more leaching than the higher growth and lower rainfall.
The third confusion is simply food.
Farming can occur without the use of synthetic nitrogen, but the outcome isn't necessarily what was intended.
The results of Sri Lanka's ban on agrichemicals, including nitrogen fertiliser, are clear. Food availability reduced, prices soared, and the economy crashed, exacerbated by lack of tourists.
The implications of the European Green Deal, requiring input reductions of agrichemical, has been calculated by the United States Department of Agriculture Economic Research Services analysis to reduce agricultural production by 7 to 12 per cent overall.
The knock-on effect has been estimated as an increase in worldwide food prices from 9 per cent (EU only adoption) to 89 per cent (global adoption).
In response to the Ukraine-Russian war, French President Emmanuel Macron has prioritised productivity ahead of the EU's Green Deal, stating that Europe cannot afford to produce less.
Future thinker Bjorn Lomberg, visiting fellow at Stanford University, agrees.
He is urging influencers, including governments and non-profit organisations, to focus on efficient agricultural production to prevent expansion into the conservation estate.
Increased use of genetic engineering, improved pest control and irrigation and fertiliser are on his list as part of the solution to feeding people.
New Zealand needs to think about the issues globally. The Select Committee did not accept Greenpeace's submission to phase out synthetic nitrogen but will be reviewing the decision in 2023.
Global forces will have changed by then, but the need to feed people will not.
Science is focused on doing that ever more efficiently through unbiased evaluation and systematic experimentation, constantly testing and re-evaluating the evidence.
- Dr Jacqueline Rowarth, Adjunct Professor Lincoln University, is a farmer-elected director of DairyNZ and Ravensdown. The analysis and conclusions above are her own. jsrowarth@gmail.com