The end of June is around halfway through grain fill of winter wheat and for the last couple of years I have had a stab at predicting the yields of the coming harvest at this stage. In 2012, I predicted below average yields, based on well below average levels of solar radiation, not just during the first half of grain fill but also in May as well. What I did not take into account was the negative impact of waterlogging during May and/or June which was very significant, particularly in parts of the Midlands.
In 2013, I predicted fairly average yields because of average radiation levels during grain fill and over the previous month and also because of the dryish soil conditions in many parts of the country. I did however predict higher than average yields for timely sown wheat in parts of Lincolnshire and further North because this part of the country received more than average radiation levels and some parts had some useful rains at the right time.
I must admit that I have less data available than in previous years for an early prediction this year but where crops have been kept weed and disease free, the yield potential looks very good. Like the good years of 1984 and 2008, we generally had a dry April but had good rains in May. Sunshine levels and limited radiation data suggest that whilst May was a bit below average, the conditions for grain fill have been better than average. In addition, we have had warm but not really hot weather, particularly during flowering. If I wanted to be picky, I would have liked the nights during grain fill to have been a little cooler so that the crop respired less of the weight it put on during the day.
There are many magnificent looking crops around and the wetter than average May has enabled them to sustain high tiller counts. I suppose the only downside was the exceptional wet winter which would have shaved-off some yield potential. Trials in very large containers (lysimeters) suggest that summer waterlogging is far more damaging to yield than winter waterlogging but the latter can have some affect.
There is still some time to go before the crop has finished putting on weight this year but it is interesting that the very high temperatures we experienced in the second and third weeks of July last year did not appear to be very damaging to yield. Not that I am saying we are almost there; in 2008, the very wet harvest compromised yields although on average they were still the highest we have achieved.
Therefore there are very solid grounds for optimism. I hope that in three weeks time I will be able to confirm this with some more accurate data than that I have available at the moment. As I have said many times before, the fundamental driver for yield potential is solar radiation. It is now clear to me that I have previously underestimated the value of good levels of solar radiation before the start of grain fill.
Wherever possible it is important that solar radiation rather than sunlight hours is measured. This is because an hour of sunlight at dawn does not provide the same level of potential energy to the crop as an hour of sunlight when the sun is at its highest. To be even more precise, only the wavelengths of radiation that the plant uses in photosynthesis should be measured (Photosynthetically Active Radiation).
Hence, I will try to improve my data sources for a final prediction over the next two to three weeks during which I hope the weather remains conducive to good yields. Here’s hoping that the wheat price will improve too.