2 June 1995


A CENTURY from now there will still be a seed time and a harvest. But global warming could have shifted their timings. It could also trigger many other changes in the way crops grow and are managed.

Even without the so-called "greenhouse-effect" the weather will continue to have a profound effect on crop production. So identifying the way temperature and rainfall affect plants is vital.

It is already leading to improved disease prediction and the prospect of less susceptible varieties in the longer term.

At the Institute of Arable Crop Research at Rothamsted researchers are forecasting a rise in atmospheric CO2, which is measured in volume parts per million (vpm). The current level is 355vpm and could rise as high as 700vpm by 2100.

Global warming

That is significant because CO2, along with other gases, absorbs infra-red radiation, prompting forecasts of global warming. In time, the atmosphere, land and oceans are projected to warm up by up to 4C.

IACR has already shown such a change could affect winter wheat production. The crop has been grown in CO2 concentrations of 355 and 700vpm and at temperatures close to ambient and ambient plus 4C.

Across six such experiments the greater CO2 concentrations accelerated photosynthesis so plants increased tiller numbers to produce more ears and more grain. Grain yield increased by 23% and straw yield by 18%.

But the higher temperature also reduced grain yield, by 20%. That nearly balances the gain from a higher CO2 level. Straw yield dropped 5% and both factors hit grain quality.

At Wolverhampton the ADAS weather unit has concerned itself with the nearer implications of climatic influences on crop diseases.

Yellow and brown rust, septoria and mildew have been studied, with yellow rust so far showing the strongest relationship with climate. Weather data correlated with figures from the MAFF National Disease Survey indicate a clear association between the incidence of severe frost – -5C and below – and the extent of carryover of the disease into the following year.

Yellow rust effects

As an example, the winter of 1981 included 21 days of severe frost and the spring of 1982 produced less than 5% of winter wheat samples showing yellow rust; conversely, the past two winters have both been very mild and the probability of yellow rust infection is higher.

From such records it should be possible to produce accurate prediction techniques upon which farmers can make varietal and crop management choices. The plant breeders can also use them to select and develop varieties more suited to changing climatic conditions. &#42