It is the time of year when I try to predict the yields of the wheat harvest. Usually I do this in early July but the timings of the blogs have meant that this year it is mid-July. It is going to be an early harvest for many and so we will soon know the true picture. Everything seems to be early in Cambridge this year. I was lifting potatoes on the 1st June and my tomatoes were ready to pick on the 10th July.
Where wheat crops had established well in the autumn, they came through the winter full of promise. Overall, it was a dry winter and so there was little waterlogging. If anything the winter was perhaps too warm but up to around the first node stage, wheat development is controlled mainly by day length which prevents crops becoming too advanced. The high yielding crop of harvest 2015 also experienced a warm and dry winter. Average temperatures in 2017 were also higher than average from April onwards, which has led to an earlier grain ripening.
Spring 2017 was exceptionally dry. Now I know that high yielding wheat years tend to have dry springs but it can be too dry leading to a reduction in yield potential. This may have been true in some parts of the country this year but the rainfall was so variable as to make it difficult to say which locations were most severely affected by drought. Rain did eventually arrive in May but in some areas there was not enough to alleviate fully the drought pressure.
Sunshine hours tended to be average or above average for every month bar February. There were really no exceptional months during the 2017 harvest year. This is unlike harvest year 2015 when April received far higher than average sunshine hours and solar radiation, particularly in the areas that achieved the very high yields. Overall, June sunshine hours were greater in 2015 than in 2017 except for East Anglia, the South East and parts of Southern Britain.
The final weather feature of note was the extreme heat in mid-June in some of the main arable areas. Temperatures were above 30 centigrade for three consecutive days and the nights were very warm too. This level of heat can cause a permanent reduction in the rate of grain fill as well as shorten the period of grain fill.
The higher than average temperatures may have reduced the period of grain fill by 4-5 days this year. In addition, the warmer weather also reduced the time between the third node stage and flowering when the potential number of grains sites is established. The percentage reductions in the times spent in these development stages may not have been compensated for by the average to above average radiation levels. Hence, in some areas this may have resulted in lower than average levels of intercepted solar radiation during these key stages.
So what are my conclusions? I think that in many parts of the country the wheat yields will do well to be above average. Second wheats seem to have particularly suffered from the lack of rainfall. However, yields in Lincolnshire and further North may be more pleasing. It is a very difficult year to attempt to predict wheat yields and I am by no means confident. So much depends on how the levels of soil moisture affected growth in individual locations. I hope I am wrong and that everyone has a great wheat harvest!