Disease-free crops cut greenhouse gas emissions

3:48pm Thursday 15th May 2008

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THE sensitive topic of gas emissions has, in the past, often been the subject of much ribald humour in Carry On films and the basis of many school boy jokes. However, in the future it will become less of a laughing matter and something to which we will all have to give considerable thought.

Recent research at High Mowthorpe conducted by Dr Neil Paveley and Dr Pete Berry has started to address this issue and has produced some interesting results.

A Defra-funded study, using data from the HGCA Recommended List trials, has shown that, with current UK wheat varieties, fungicides are reducing greenhouse gas emissions by between one and two million tonnes of carbon dioxide equivalent (a universal measure of greenhouse gas emissions) each year. In addition, fungicide use is also reducing the land area required to maintain current wheat production by approximately 400,000ha.

This is because most of the greenhouse gases produced by arable farming are associated with the application of nitrogen used to grow the green area with which crops photosynthesise. On average 2.5m tonnes of carbon dioxide equivalent are released per hectare, as a result of the energy used to manufacture nitrogen fertilisers and the nitrous oxide released after their application. In contrast, the greenhouse gases released by the manufacture and application of fungicides are very small. Manufacture accounts for about 4kg/ha and application for about 8kg/ha.

The potential for fungicide use to reduce greenhouse gas emissions is a difficult concept to grasp. However, there is a rationale. Imagine you have two wheat crops, one fungicide-treated and the other untreated. Both crops will generally receive the same amount of nitrogen. In the treated crop there will be a greenhouse gas emission cost from manufacture and use of fungicides. However, this will be small in comparison with nitrogen use, so the CO2 emitted to produce the two crops will be similar. In the untreated crop on average there will be 1.8t/ha less grain than in the treated crop. Consequently per tonne of grain produced the CO2 equivalent in the untreated crop will be greater than for the treated. The value of this difference will be about 60kg CO2 equivalent per tonne.

If in future loss of fungicides, fungicide resistance or excessive regulation means that farmers are less able to control diseases it could mean an extra million tonnes of greenhouse gases a year. This is the same as about 100,000 return flights from London to Sydney, to produce our UK average wheat output of 15m tonnes. This assumes that the extra 400,000ha required to produce the additional yield lost due to disease all comes from land already in production. If half of that land came out of grassland, the greenhouse gas costs would double.

By using fungicides responsibly to control diseases it may be possible to make a positive contribution to reducing greenhouse gas emissions.

- Dr Steven Ellis, entomologist at ADAS