Comment: While some agricultural systems produce fewer greenhouse gases (GHG) than others - all produce some, writes Dr Jacqueline Rowarth.

Producing food has an impact on the environment. Whatever the food, whatever the system, there is an impact.

Land requirement can be reduced by growing tomatoes in greenhouses, but the trade-off is building materials and energy, with greenhouse gas (GHG) implications.

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Moving hens from outside into barns improves air quality and improves longevity, but again requires facilities.

Growing apples instead of pasture for cows reduces methane but increases requirements for pest and disease control, with consequent GHG associated.

Anything that increases fossil fuel use increases GHG, the impact of which lasts for centuries. This means that the current focus on uncoupling food production from impacts is fraught with difficulties.

Climate-friendly agriculture is being promoted as the way forward, without any clear understanding of how it can be achieved.

Greenpeace has promoted theories about regenerative organic agriculture and plant-based foods in its call to the Government for a billion-dollar investment, but while some systems produce fewer greenhouse gases (GHG) than others, all produce some. And not all the claims being made about the benefits of organic and regenerative are justified.

With current technologies, the Paris agreement to limit warming to "well below 2°C' " will reduce food supply – the estimate is that another 80million to 300 million people will be undernourished by 2050.

If the goal in farming is feeding an increasing population with least impact, conventional agriculture is the approach most likely to be successful, says a report published in 2017 by University of Minnesota researchers Dr Michael Clark (who contributed to the EAT Lancet report) and Professor of Ecology David Tilman.

Their meta-analysis is the most comprehensive Life Cycle Assessment comparison currently available and the results are available on "Our World in Data".


They concluded that per unit of food, organic systems require more land and cause more eutrophication than conventional systems. Although they use less energy, they emit more greenhouse gases, which means that increases in agricultural input use efficiency would offer larger environmental benefits than would a switch to organic agriculture.

The researchers acknowledged that organic systems generally have higher organic matter and soil biodiversity than conventional farms but pointed out that the requirement for more land area per unit of food production had the potential to reduce soil organic matter from its "native" status.

If the goal in farming is to minimise environmental impact per hectare, organic systems could be the way forward – except that more land would be needed to feed the population, with implications for loss of biodiversity.

Technological advances save native land from being brought into cultivation.

Dr Jacqueline Rowath. Photo / Supplied
Dr Jacqueline Rowath. Photo / Supplied

Technology adoption means that New Zealand conventional agriculture is a long way from the "high input monocultures and industrialisation" used to describe the bulk of New Zealand's agriculture throughout the Greenpeace investment request.

The description is referenced to a global report from the US where the farming is at a very different scale from that in New Zealand. The US Department of Agriculture has reported that regenerative and organic agriculture can increase soil organic matter.

The starting point for the depleted soil was 1 per cent. New Zealand cropping soils are around 5 per cent and pastoral soils are 8 per cent. They are not depleted.

The one-billion-dollar investment requested by Greenpeace also covered plant-based food processing.

Much hype surrounds the global potential for plant protein to replace animal protein, and most of the calculations of the benefits overlook the limitations in amino acids in a plant-based diet and hence supplements required for health.

They also overlook the impacts of growing plants and then processing them into something that looks like some form of meat or "milk".

Listen to Jamie Mackay interview Dr Jacqueline Rowarth on The Country below:

In addition, the economic viability of protein crops in New Zealand, even with a government-funded kick start, is under question.

Most plant proteins used in food manufacture in New Zealand are imported because the growing and transport costs are not as great as the cost of growing the crop in New Zealand.

Different environments suit different production systems. New Zealand is a very efficient producer of animal protein from land that is mostly not suitable for cropping or food trees.

In 2019, Prime Minister Ardern stated to the United Nations that we are determined to show that we can be the most sustainable food producers in the world.

Todd Muller, now leader of the National Party, responded that we already are.

And farmers are endeavouring to do even better as the technologies are developed.

Emeritus Professor Anthony Trewavas, of the University of Edinburgh, has written extensively on the problem of feeding the world while reducing environmental impact.

His conclusions are simple: "Today's global problems - such as climate change and population growth - need agricultural pragmatism and flexibility, not ideology."

He has also stated that it is "essential that all scientists assert the primacy of properly established and critically assessed scientific knowledge".

The assessment needs to be in context to have any meaning; what applies overseas does not necessarily apply here.

- Dr Jacqueline Rowarth CNZM CRSNZ HFNZIAHS has an Agricultural Science degree from Massey University, with honours in Environmental Agriculture. Her PhD is in Soil Science. The analysis and conclusions above are her own.