"Frequent and often heavy rain showers" slowed harvesting to less than half the typical pace in the last week, with Scottish farmers now behind average pace in reaping spring barley.
The slowdown came despite growers choosing to gather in crops at up to 25% moisture levels and protect returns boosted by prices at historically high levels.
"The majority of the grain harvested over the last week was harvested at high moistures in the gaps between showers," consultancy Adas, which undertook the harvest survey, said, noting that temperatures were two degrees Celsius below average too.
"As a result, 80-90% of the grain harvested has required at least some drying."
‘Quality starting to drop’
However, the spec of grain has deteriorated despite farmers’ efforts, with Adas flagging "signs that quality of any remaining milling wheat is starting to drop".
"Milling crops usually get priority at harvest, but where harvesting has been delayed there are reports of deteriorating in Hagberg falling number to below the acceptable standard."
The Hagberg falling number is one of the measures of a wheat sample’s suitability for making dough.
In spring barley, Adas edged its yield forecast lower to 5.0-5.3 tonnes per hectare, from 5.1-5.3 tonnes per hectare.
For oats, which had looked set for a bumper yield of up to 6.2 tonnes per hectare, matching a 2003 high, the estimate was cut back to 5.7 tonnes per hectare, in line with the long-term average.
However, Adas restated its optimism over winter-sown oilseed rape – the great majority of the UK crop – for which the yield estimate was lifted by 0.2 tonnes per hectare to 3.8-3.9 tonnes per hectare, on track to set a record by a distance despite the dry spring.
"Winter oilseed rape yields have been particularly good, with most crops exceeding expectations."
Adas vs ODA
The findings are comparable with those released on Wednesday by Offre & Demande Agricole, which forecast a rise of 10.5% in UK rapeseed production this year, implying an extra 230,000 tonnes or so.
For wheat, ODA estimated the yield falling 3.4%, implying a figure of about 7.5%, within the range of Adas forecasts, although the French-based consultancy, which is expanding in the UK, was more upbeat on barley yields.
For spring barley, "the grading percentage for malting is close to 90%," ODA added.
London wheat for November stood at £173.00 a tonne on Thursday morning, down 1.0% on the day but well above levels below £100 a tonne before the grains rally kicked off in late June last year