Fungicides help slow down climate change, according to new research. Mike Abram reports

Maximising disease control not only protects profits, but also looks after the environment, new research has found.

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 1 and 2m tonnes of carbon dioxide equivalent (see box) each year.

They are also reducing the land area required to maintain wheat production by about 400,000ha.

Most of the greenhouse gases from arable farming are associated with nitrogen used to grow green canopy for photosynthesis, says Neil Paveley of ADAS. “Typically, 2.5m tonnes/ha of carbon dioxide equivalent are released as result of the energy used to manufacture N and the nitrous oxide released after N applications.”

In contrast the greenhouse gases released by producing and applying fungicides is very small, about 4kg/ha in making products and 8kg/ha to apply them. Incorporating disease resistance genes into new varieties similarly has little greenhouse gas cost. “But the yield effects from both are substantial.”

Optimum N

Using fungicides also increases the optimum amount of N growers can apply without any deleterious effect on greenhouse gas emissions, BASF research has found.
The trials compared wheat grown with various nitrogen doses, sprayed with either no fungicide, 0.5 litres/ha of Opus (epoxiconazole), Opus + boscalid (eg, Tracker) or Opus + boscalid + Comet (pyraclostrobin) at T1 and T2.
The results showed increasing yields with increasing inputs, but also that the optimum dose of N also increased, Bill Clark, director of Broom’s Barn, says.
That doesn’t mean higher nitrogen emissions though. “Environmentally it is not a bad thing because it is all being used – you get more N recovered from the soil.”
N use efficiency is also higher – more grain is produced per kilogram of N applied, he adds.

The average yield response from using fungicides in the HGCA RL trials is about 1.8t/ha. This level of yield loss, after allowing for the reduction of greenhouse gases associated with the manufacture and application of fungicides, results in a net increase in emissions of about 60kg CO2 equivalent per tonne of grain where fungicides are not used. “That number is big enough to matter.”

If growers lost the ability to control diseases – either through loss of fungicides, fungicide resistance or excessive regulation – the implication would be an extra 1m tonnes of greenhouse gases a year, the same as about 90,000 return flights from London to Sydney, to produce our UK average wheat output of 15m tonnes, Pete Berry, also of ADAS, calculates.

That’s assuming the extra 400,000ha required to produce the extra yield lost through diseases all comes from land already in production, he says. “If half of that land came out of grassland the greenhouse gas costs would double, while if it came from chopping down tropical rainforest it would increase to 6m tonnes.”

The research won’t change growers’ disease control strategies, Dr Paveley admits. “But at farm level in the future growers will have to think about carbon consequences of what they are doing.”

That could be especially true if government plans for bioethanol production, for example, in 2010 become reality. Under the proposals the plan is to reward biofuel use on the amount of greenhouse gas they save, and those rewards could be passed on down the chain. “In theory, farmers should receive greater payments for grain produced with less greenhouse gas,” Dr Berry says.

Using fungicides also increases the optimum amount of N growers can apply without any deleterious effect on greenhouse gas emissions, BASF research has found.

The trials compared wheat grown with various nitrogen doses, sprayed with either no fungicide, 0.5 litres/ha of Opus (epoxiconazole), Opus + boscalid (eg, Tracker) or Opus + boscalid + Comet (pyraclostrobin) at T1 and T2.

The results showed increasing yields with increasing inputs, but also that the optimum dose of N also increased, Bill Clark, director of Broom’s Barn, says.

That doesn’t mean higher nitrogen emissions though. “Environmentally it is not a bad thing because it is all being used – you get more N recovered from the soil.”

N use efficiency is also higher – more grain is produced per kilogram of N applied, he adds.

Fungicides and optimum N use

 

Untreated

Opus

Opus + boscalid

Opus + boscalid + Comet

Fungicide cost

£0

£25/ha

£65/ha

£95/ha

Yield @ N optimum

5.52t/ha

7.41t/ha

¤8.46 t/ha

9.06 t/ha

Grower profit

£419/ha

£656/ha

£776/ha

£829/ha

N optimum (3:1)

76kg/ha

124kg/ha

119kg/ha

137kg/ha

Production cost (£/t)

74

61

58

59

Land required (kha/m tonnes)

181

135

118

110

Carbon dioxide equivalent

Different greenhouse gases have different effects on global warming. For example, nitrous oxide has about 300 times the effect of carbon dioxide. Carbon dioxide equivalent converts all these effects into the equivalent amount of carbon dioxide, to express all the greenhouse gas consequences as a single value.