BASF Agricultural Solutions UK

New research reveals culprit for 2020 OSR yields

By Clare Tucker, Business Development Manager BASF

Recent research by ADAS in partnership with BASF demonstrates how weather, not cabbage stem flea beetles, were the biggest factor in determining 2020 OSR yields.

Here, I catch up with Yield Enhancement Network (YEN) growers, Adrian Joynt and Chris Eglington to find out their thoughts on the findings. But first, you’ll need to know more about the research:

ADAS conducted a meta-analysis of weather and OSR yield data from the last 40 years. It revealed both the ‘perfect storms’ and ‘ideal conditions’ leading to the highs and lows of record-breaking years.

The research also showed how, over these four decades, weather was responsible for up to 37% of the OSR yield variation and provided insights into OSR management specifically designed to help crops cope with extreme conditions.

2020 was not the lowest year in terms of average OSR yields, that unenviable award goes to 2001, according to Dr Pete Berry, Head of Crop Physiology at ADAS who presented the findings. “While damage caused by cabbage stem flea beetles (CSFBs) undoubtedly made a significant contribution last year, the weather was the key factor in determining yields.”

According to the research, the long-range forecast needed for the highest yields is: a high maximum temperature in October; a dry December; a warm minimum temperature in March; a sunny and dry April; and, and a cool, wet May.

“In 2020, the only month that ‘played ball’ was April even then, the sunshine was accompanied by a drought,” he notes.

“To give OSR crops the best chance of coping with such adverse weather conditions, they need strong autumn growth and a healthy canopy for as long as possible.

“Choosing varieties with early vigour and maximising seed to soil contact and moisture availability at drilling, will help crops grow above and below ground. This strong establishment will enable them to cope better with cold wet weather throughout the autumn/winter and withstand more damage from CSFBs.”

For Adrian, drilling date is highly influential in establishment. Typically, he waits until the last week in August before sowing his OSR on his 2,400 acre farm in South East Shropshire.

“For the last two years, it’s been wetter in August than in September here,” observes Adrian. “CSFBs also seem to be moving into the crop September rather than August, this combination means our later sown crops are not looking as good as the earlier drilled. It’s making me wonder whether I ought to bring our drilling forward in future.”

Norfolk grower, Chris, achieved robust soil to seed contact by double, sometimes, triple rolling. “My OSR drill doesn’t like wet conditions so we try to drill when conditions are drier with the assumption that any rain that follows will kick-start growth.

“It’s helpful if the crop all comes up the same-time. This seems to dilute the effects of CSFB. Where the crop emerges at different times, the beetles just keep going and will annihilate newly emerging plants as they come through.”

This year, some of Adrian’s OSR seed has a high TSW – a factor positively associated with higher yields in this year’s YEN.

“The cotyledons were big,” notes Adrian. “The crop was sown on 4th September when CSFB pressure was high and I’m sure the robustness of these early leaves helped the crop to cope with the damage.”

In 2020, monitoring of eight BASF Real Results showed how some low-yielding crops went backwards in March. “We suspect this may be due to a combination of winter water logging impairing root function and low nutrient availability. Soils will have leached nitrogen during the wet winter months. Add this to late fertiliser applications and delayed uptake due to the drought in spring, and it is no wonder crops struggled,” says Pete.

Usually, a dry and sunny April provides OSR with ideal conditions needed to preserve yield potential. More than average sunshine in the month increases pod and seed set and less rainfall prevents crops producing an overly large canopy, optimising GAI.

Chris tried an alternative approach to managing the canopy, running a grazing trial on some of his OSR acreage. “We had 500 ewes on the crop and by luck, took the off just before we’d torrential rain. It took just seven days and interestingly, the sheep choose the volunteer barley and the conservation headlands before the OSR. While we still applied Caryx® to keep the crop in check, the sheep did their job.”

A May that is 1C cooler than average, sees crops set more pods and seed. Where that cooler weather is accompanied by higher than average rainfall, they will also have the water needed for optimum seed fill during the summer.“

Growers can assist OSR during April and May by using N fertiliser applications and PGRs to hold crops at ideal GAI while stimulating lower order branching to increase seed number. Careful timing of fungicides applications to minimise Sclerotinia and prolong green leaf area will further help to maximise photosynthesis.”

ADAS also looked at some BASF Real Results case studies. These included a low yielding site with no CSFB larvae in spring and a comparatively high-yielding site with an average of 36 larvae / plant, providing further evidence that the weather was the key limiting factor for OSR yields in 2020.

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