Growers told to cut seed rates

Article taken from The Press and Journal Farming

Scottish oilseed rape growers are being urged to reduce seed rates to produce the correct crop structure needed to deliver top yields.

At a technical meeting hosted by Agrovista at Foveran Hall, Ellon, technical manager Chris Martin explained that over the four years the national network of Growcrop Gold oilseed rape trials had been running, highest yields had always been achieved with lower seed rates on good seedbeds where there was adequate moisture.  While taking the leap of faith to cut seed rates could be daunting, not doing so would prove costly, he said.

“The components of oilseed rape yield are maximising seed number and allowing seeds to be as heavy as possible.  A plant’s seed numbers are set in the two or three weeks after the end of flowering, the challenge thereafter is to ensure seeds fill well by keeping plants healthy to maximise photosynthesis, which can be achieved by having a green area index (GAI) of 3.5-4 at flowering.

The 2013 Growcrop Gold results reflect the previous years’ findings – there is an optimum plant canopy shape, which is best achieved at 25-30 established plants per square metre in the spring.  “If crops are too thin, they will have insufficient green leaf area to harvest the sun’s energy, and if they are too dense, the resulting mass of flowers will reflect up to 60% of light away from the crop, disease risk will increase from the humid microclimate generated between plants, and losses from increased lodging risk could amount to 505,” Mr Martin said.

One of his most important observations was that plant populations had to be right at sowing.  “In our plant pot trials, I’ve seen rape plants that are too crowded at sowing, grow tall and think, instead of developing into the ideal – a shorter plant, with an optimum of eight to nine primary branches.

“In addition to this secondary branches are also crucial because they can deliver upward of 1t/ha in extra yield.  And what is really interesting is that a plant subjected to early competition will retain ‘competition memory’ in its canopy shape through to harvest, even if plant numbers are mechanically reduced; so there’s no going back once you’ve planted.”

Added to this, the competition between oilseed rape plants within the same row appears to be more important than between rows.  “Typically the highest yields we’ve recorded, regardless of row spacing, are where we have spring plant populations of 12-15 plants per linear metre.”  To complete the picture, at higher seed rates, there was a reduction in the percentage establishment, he added.

“Unlike wheat and barley, oilseed rape is relatively new crop to Scotland and we still need to learn a lot about it,” said Mr Martin.  “The theoretical yield for UK grown oilseed rape is 12t/ha, yet the average yield actually achieved on farm is 3-4t/ha.  One of the reasons we set up the Growcrop Gold trials was to see how we can bridge this yield gap.”

One of those attending the meeting was HGCA monitor farmer Andrew Booth of Savock Farm, Foveran.

Agrovista agronomist Lewis McKerrow said: “This year the Booths have invested in a Sumo subsoiler drill after a few years trialling similar systems as part of the monitor farm group.  The Sumo removes soil compaction and sows rape at 50cm row widths – proven in our trials to be the optimal row width for rape when combined with the correct seed rate.”

With some very advanced oilseed rape crops at almost knee height in the north-east, Mr McKerrow said the focus next spring needed to be on keeping plants short and encouraging lateral branching.

“This will mean delays in nitrogen applications, and the use of a growth regulator, particularly if growth-regulating fungicides – metconazole or tebuconazole – were not applied this autumn.

“I’d recommend a stem extension application of Caryx next spring, the first specific oilseed rape plant growth regulator launched earlier this year.


23 November 2013

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