Shedding new light on specific weight

New analysis of HGCA data has shown late ripening wheat varieties tend to have lower specific weights but higher yields.

The research, prompted by the quality of last year’s harvest, looked at data from 1994 to 2012 from Recommended List trials and the AHDB/HGCA Cereal Quality Survey. It examined the effect of weather, varietal traits and region on final specific weight.

“One of the most interesting findings is that later ripening varieties tend to have lower specific weights but higher yields,” according to Dr Ellie Marshall, research and knowledge transfer manager at HGCA. “Crucially, the difference between the specific weight achieved in Recommended List trials and commercial crops is much greater in later ripening varieties.”

In recent years, there has been a shift to more late ripening varieties and this has been matched by more being grown on-farm. The main reason for the shift is that these varieties tend to have higher yields which is one of the main factors growers look for in their crops.

“The research shows that the specific weight problems of 2012 are likely to have been exacerbated by late maturity but we can’t forget that the weather was the most important factor. Growers should consider having a range of maturities in order to achieve both consistent yields and quality in each season,” explains Dr Marshall.
2012 was undoubtedly an exceptional year.  From 2007 to 2011, the specific weights of Recommended List trial samples closely mirrored those in AHDB/HGCA Cereal Quality Survey of commercial samples. 

In 2012, the average specific weight for Recommended List samples fell just short of 72kg/hl, while crops in the Cereal Quality Survey were even further behind at 69 kg/hl. This is attributed to the far more robust fungicide programme used for the Recommended List in comparison to many commercial farms. However, even with robust treatments, specific weight was still considerably lower in 2012 indicating that the weather played a key role.

“April 2012 was wet and gloomy which slowed plant development and reduced grain number.  These conditions returned during the growth and grain filling months of June and July which saw higher than average rainfall coupled with low light levels, particularly in June.  These combined to produce lower specific weights and a delayed harvest in many parts of the country,” according to Dr. Marshall.

The research also looked at regional differences in the specific weights of commercial crops. The most striking finding was that in 2012, the South West and Midlands had the lowest specific weights of about 68 kg/hl, whereas in previous seasons, specific weights in these regions were among the highest in the UK.

Average specific weights in other parts of the UK were very similar to one another at around 70k g/hl, this was even the case in Scotland which typically has lower specific weights. 

The research has not yet shown whether variety choice, weather or other factors were the main cause of these regional variations.

For the longer-term, HGCA has set up a network of weather stations to help researchers look in greater detail at how weather influences crop development. More information on regional and varietal differences will also come out of HGCA’s Cropping Systems Platform project which will have four UK sites for the 2013/2014 growing season.

Download the full report here.

Wheat in the Hulah valley, 2007 (Photo credit: Wikipedia)