NIAB - National Institute of Agricultural Botany

Orson's Oracle

Wheat yields revisited

Posted on 08/08/2013 by Jim Orson

I was in the garden on Sunday morning when my mobile rang. The call was from a farmer on the coast of Essex saying that his wheat was yielding well above average and the quality was superb.

What obviously stimulated his call was last week’s blog suggesting that, overall, timely drilled wheat would not yield more than average; ‘overall’ does not mean in every case. In his case it could be that wheat on the east coastal strip did not experience the extreme temperatures in July as in central England.

So I’ve been checking that my prediction was not too ‘Cambridge-centric’. We did seem to miss some rainstorms and we may have experienced more days with very high temperatures in early and mid-July than others. There is now good information to check weather data over the UK on the Met. Office website.

These data show that much of the country was very dry through April to the end of June. The July maps are difficult to interpret as much of the rain fell after grain fill had been completed. However, there were exceptions and North East England (north of the Humber) had a good level of rain in May. The North East also did not have such extreme temperatures as much of central and southern England and so this area may have better than average yields from timely sown wheat. Time will tell.

I also have further information provided by UEA/Weatherquest.  It’s a solar radiation map of the UK which covers a period that approximates to grain fill. This confirms the information that has been appearing on the members’ section of the NIAB TAG website. Much of the country received about average levels of solar radiation during grain fill but there are exceptions with the South Wales coast, the coast of South West England and (wait for it) much of the cereal growing areas north of the Humber receiving above average levels.

They say that when you are in a hole you should stop digging. However, while I stick to what I said in last week’s blog, there might be areas of the country, particularly North East England (north of the Humber) which have better than average yields. Again, only time will tell.

Much of what I said last week was based on the possible impact of high temperatures and/or drought on the grain fill of wheat and I have been ploughing through the scientific literature on the subject. As you can imagine, it is enormously complex. There is general agreement that high temperatures and drought during grain fill can reduce yields but it is not clear what is too high a temperature. 

One detailed paper suggests that the earlier there is heat stress and/or drought stress during grain fill, the greater the impact on yield. In this paper, the heat stress treatment was 28 degrees C during the day and 20 degrees at night compared to 23 during the day and 15 at night. This year the hot weather occurred towards the end of grain fill but in many areas the crops were short of moisture throughout grain fill. This suggests that moisture stress may have a bigger impact on restricting yields than the high July temperatures. Again this suggests that the North East may have higher than average yields.

There are some other interesting pieces of information. One paper concludes that increased night time temperatures have a greater impact on wheat yields than an equivalent increase in day time temperatures. This is of particular interest as night time temperatures during grain fill have been increasing at the NIAB TAG site at Morley for a number of years.

Another paper suggests that when grain fill is restricted by heat, the transport to the developing grain of stem reserves accumulated before anthesis (when the anthers show) becomes more efficient. Varieties introduced over the last few years accumulate more stem reserves than those previously introduced, so this may partly mitigate the possible impact of drought and heat on grain yield this year. Nevertheless, at the moment I am sticking to my guns.   

 

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