greenhouse gas emissions may actually rise by 100% organic farming

  • Moving to 100% organic farming would reduce food yields by up to 40%, says new research by Cranfield University
  • Direct greenhouse gas emissions are reduced with organic farming
  • But increased overseas land use to compensate for food shortfalls means net emissions are greater
  • Storing carbon in the soil – sequestration – offsets only a small part of the higher overseas emissions

A 100% shift to organic farming in England and Wales [1] would yield up to 40% less food if the nation did not change its diet, leading to increased imports and a net increase in greenhouse gas emissions, researchers have found. The study, published today in Nature Communications was principally conducted by Dr Laurence Smith, whilst at Cranfield University (now of the Royal Agricultural University), with Professor Guy Kirk and Dr Adrian Williams of Cranfield University and Philip Jones of Reading University.

Organic farming produces less emissions, but produces less food

Although organic farming generally creates lower greenhouse gas (GHG) emissions per commodity, up to 20% lower for crops and 4% for livestock, it also produces less food energy output per hectare.

Dr Adrian Williams, Reader in Agri-Environmental Systems at Cranfield University says, “We predict a drop in total food production of 40% under a fully organic farming regime, compared to conventional farming, if we keep to the same national diet. This results from lower crop yields, because yields are restricted by a lower supply of nitrogen, which is mainly from grass-legume leys within crop rotations or manure from cattle on pasture.”

Assessing the need for imports to make up the shortfall, and assuming that food diets and demands stay the same, the academic team estimates that the overseas land area needed to be changed to food production for England and Wales would increase by a factor of five. This additional land would likely be of sub-optimal quality and therefore not as productive as higher-quality land.

Dr Laurence Smith says, “Although resource use can be improved under organic management, there is a need to consider the potential effect on land-use. Under a 100% organic scenario in England and Wales, a net-reduction in greenhouse gases would only be achievable if accompanied by a major increase in organic yields or widespread changes to national diets.”

Storing carbon in the soil

Rates of carbon sequestration – where atmospheric carbon dioxide is captured by plants and stored in the soil – are higher under organic farming because of greater use of manures and longer crop rotations. However, this is limited to the first decade or two following conversion to organic farming, as the soil will eventually reach a steady-state when carbon sequestration rates fall to zero. Overall in the 100% organic farming modelling, it was found that sequestration only offsets a small part of the higher emissions from overseas land use.

Net emissions are greater

The research concluded that net GHG emissions under a 100% organic farming production method could increase by 21% over conventional farming baselines -under the assumption that only half the extra overseas land was converted from grassland – going up to 170% if the Carbon Opportunity Cost [2] is added in. 

Guy Kirk, Professor of Soil Systems at Cranfield University, says: “Although there are undoubted local environmental benefits to organic farming practices, including soil carbon storage, reduced exposure to pesticides and improved biodiversity, we need to set these against the requirement for greater production elsewhere.”

Dr Adrian Williams concludes, “The assumption about diets is crucial: today’s organic consumers are a self-selecting group and not typical of the nation. Whether a different national diet could be provided by the same land area under all organic production is a different study. This was aimed at understanding limits to production. The study was based on rigorous modelling that had its foundations in establishing the biophysical limits of crop production without manufactured nitrogen.”

The greenhouse gas impacts of converting food production in England and Wales to organic methods was published in the journal Nature Communications on Tuesday 22 October by academics from Cranfield University, the Royal Agricultural University and the University of Reading.

Further detailed findings:

Impacts on crops and yields:

The research team found that purely organic farming would:

  • Increase beef cattle and sheep numbers, because of the increase in pasturelands. However, the volume of meat would not increase because of slower production rates.
  • Pigs and poultry, and eggs, would decrease, because there would be less concentrated feed available. Dairy cattle numbers and milk production would decline for similar reasons.
  • Production of potatoes, carrots, peas and beans would increase, but production of wheat would decrease more.
  • Certain crops, such as oil seeds, would hardly be grown in a fully organic system.

Carbon Sequestration

The research showed that the amount of carbon sequestered would be much less than the amount lost during overseas land conversion to provide more imported food , because conversion would be mostly from carbon-rich grassland soils. The carbon balance for wholly organic production is even more negative if the amount of carbon that could be sequestered if the land were instead used to maximize its carbon storage potential – for example by converting it to the productive forest – is factored in: the so-called “Carbon Opportunity Cost”.

source from cranfield university

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