Significant rain is needed in the next few weeks to prevent yield loss in crops, according to ADAS‘s Susan Twining.

“Soil moisture deficits are higher than they have been for the past four years,” she told Farmers Weekly at the ADAS Boxworth open day. “If you have a sustained soil moisture deficit of over 75mm on light land and 120-125mm on heavy soil then there is potential for yield effects.”

Soil moisture deficits on medium soils were around 110mm, she noted. “We’re going to need significant rainfall before harvest.”

The average wheat crop needed around 350mm of water between April and harvest from all sources, she explained. “It needs sufficient moisture to maintain green leaf into grain fill, and then more to make sure grains fill properly.”

On medium soils crops normally got around 200mm from the soil, which left around 150mm required from rain. “So far, we’ve had on average only 50mm across the country. It is beginning to get serious – soil moisture deficits are high at this stage and there is quite a lot more growth to do.”

But not all was not lost, she stressed, even though no significant rain was forecast for the next fortnight. “It is still too early to call whether yield has been lost. Physiologically for wheat there is no reason why we cannot have good yields – don’t forget we often have highest yields in years of mild drought.

“If we get rain in the next month and then it turns cool but sunny we might wonder what we were worried about.”

Severe droughts caused around 1.5t/ha yield loss in 1976, she said. “Yields were lower then, so a really severe drought might cause more loss now.”

More stories from ADAS Boxworth open day:

• Stacking pre-emergence blackgrass herbicides might be effective
• Triticale could be alternative second cereal
• Nitrous oxide emissions measured
• Blackgrass sampling advice
• Applying nitrogen to flowering oilseed rape could increase yields