Harvest progress

15 Aug 2013

It is still too early to get a good overview of the yields of timely sown wheats.  Some reports say that the yields are ‘nothing special’ and others are saying that yields have been slightly above average.  So the jury is still out on my overall prediction that timely sown wheats will not yield above average.

As regular readers of this blog will know, this prediction was based on the fact that yield potential is influenced significantly by the amount of solar radiation intercepted by the crop and this year this has been about average.   Potential yields are, almost by definition, never achieved and I think that this year’s dry and hot conditions during grain fill will not see yields being any closer to the potential than usual.

What I may have overlooked is the impact of the long cool spring on wheat yields.  This seems to have benefited the yields of well established winter oilseed rape crops and may also have had a positive influence on wheat yields.  Indeed, warmer than average weather from the start of stem extension was cited as a negative factor for yield in an analysis of why French wheat yields are plateauing.

In fact the harvest so far indicates that it was a good spring but that crops were slowly running out of water. So whilst autumn sown crops that matured earlier have done relatively well, wheat which needs good supplies of water for longer into the summer may not have done as well, particularly on lighter soils and in areas that were particularly dry.  It is interesting to note that in north western Europe, wheat yields relative to oilseed rape yields are generally higher than in the drier parts of Europe, again reflecting wheat’s requirement for water later into the summer.

Another clue to wheat running short on moisture this year is the very good quality of the crop.  Hagberg falling numbers and proteins are good.   This reflects research done by the University of Reading and published in 2003.  In experiments when the crop was ‘droughted’ for a 14 day spell during grain fill, yield started to suffer once water supplies were below 70% of the potential held by the soil (available water capacity).  At the same time, Hagberg falling number values and protein levels increased.  Thousand grain weights particularly suffered from this period of water shortage and a separate experiment indicated that the earlier during grain fill that moisture became restricted and/or high temperatures occurred, then the greater the impact on grain weight.

What is not so easy to explain in these experiments is that this period of water shortage mid-grain fill also reduced specific weights, which are incidentally also reported to be good this year.  However, specific weights are notoriously difficult to predict.  It could be that this season’s cold winter and spring reduced the number of grains set leading to well-shaped grain despite the fact that the dry conditions reduced grain fill.

So the dry and perhaps hot conditions during the grain fill of wheat this year may have had a significant impact on both yield and quality of the wheat crop. I await with particular interest the yields of wheat in north eastern England.   Theoretically at least, yields are more promising in that area.  I will try to summarise my thoughts once the yield patterns across the country become clearer.  In the meantime, we are off to France for a nine day holiday.  Yes, I have to admit, it is tough being semi-retired.