Wheat yields – not just a great summer

16 Oct 2015

My blog in early July suggested that yields might be good except in those parts of the country where a very dry May/June could limit the yield potential on all but the most moisture retentive soils. This was along the right lines and yields have been exceptionally high in some areas but the dry conditions in May/June perhaps did not limit yields as much as I thought they would.

So I have revisited some of the weather data I reviewed for the July blog in order to try to explain the exceptionally high yields experienced by some growers. Unfortunately, I am still pursuing solar radiation data that is hard to come by and will continue with my quest. In the meantime I thought I would set out my preliminary thoughts in this blog.

The solar radiation data that I have, and which does not cover some of the extremely high yielding areas, suggest that it was well above average for the whole growing season. However, it was not exceptionally high during grain fill.

Overall, temperatures from January to July were very close to average for the arable areas of England. In the July blog I noted that the cool nights in June could be beneficial only because the crop would not respire overnight so much of the gains made during the day. These cooler than average overnight temperatures were a particular feature in North Yorkshire and Northumberland where some of the highest yields occurred. These areas also had good levels of rainfall in May/June.

What may also have been very significant in determining yields this year was the higher than average amounts of solar radiation in March, April and May. The amounts in April were exceptionally high. This may have resulted in higher than average levels of tiller growth and survival, grain sites/ear and stem reserves. Hence, it may be reasonable to suggest that the higher yield potential established in the spring was realised by much better than average, but not exceptional, conditions during grain fill. It is interesting to note that a recent AHDB (the old HGCA) Project Report 496 suggests that modern wheat varieties have higher levels of stem reserves than those introduced over a decade or two ago.

My July blog suggested that overall yields would be higher north of the Wash because of rainfall patterns and the fact that temperatures on the 1st July were not as exceptionally high as those which occurred further south. We will never know the impact, if any, of that very hot day on final yields.

So it seems that there was no one standout feature that resulted in the very high yields this year. On the other hand, the weather throughout the year favoured high yields. The crops wintered well, with little or no waterlogging, and experienced very favourable weather in the spring and summer, except in those areas which suffered from drought stress during May/June.

There will be another blog on this issue when I have more data on the structure of some of the very high yielding crops and on the weather, particularly solar radiation.