High seed set is key to top yields

Article taken from The Northern Farmer, written by Wendy Short

Growers received expert advice on oilseed rape canopy management and an update on Agrovista’s Growcrop Gold oilseed rape trials, at a recent meeting near Northallerton.

Achieving high seed set rates was crucial to maximising yields, explained Dr Pete Berry, of ADAS.  This stage occurred two to three weeks post-flowering and would required careful management.

“A crop with a large, uniform canopy may look promising, but an over-sized, thick flower layer will intercept light and prevent it from reaching other photo-synthetically-active areas of the plant,” said Dr Berry.

“Therefore, yields are likely to be disappointing.  It can also greatly increase the risk of lodging, which cause losses as high as 50 per cent.

“It’s best to aim for a Green Area Index (GAI) of 3.5 at flowering, to maximise the number of seeds set per square metre.

“Phone apps, which use a photograph of the crop to estimate GAI, are useful.  However, they rely on measuring the percentage of ground that is visible, relative to the crop, so they lose accuracy as crop size increases.”

The correct use of nitrogen (N) to manipulate crop growth pattern was an essential management tool, he told growers.  Timing was critical, with studies suggesting that later applications would normally prove more effective.

He cited a trial in which two treatments of 120kgs/nitrogen/ha were applied on March 10 and April 12, with yields averaging 4.47t/ha.  Meanwhile, the same total amount of fertiliser total amount of fertiliser, but with 140kgs/N/ha applied on April 12 and 100kgs/N/ha on April 25, produced yields of 4.78t/ha.

Dr Berry said: “It may require some courage to hold off N applications until later in the season, but research shows that it does benefit the crop.  It N is applied too early, it will simply increase stem length and heighten the risk of lodging.”

He reminded growers that the crop must take up about 50kgs/N/ha, to produce one GAI.  In general, N fertiliser was 60 per cent efficient, but the figure varied widely, depending on water-logging, soil type and other factors.

Achieving an optimum GAI of 3.5 at flowering was generally considered sufficient to achieve 3.5t/ha.  An additional 30kgs of applied N were required to produce every extra 0.5t of oilseed rape, above a 3.5t/ha yield.

“As the seeds develop they take N from the pod wall and the canopy starts to die off.  If there is insufficient nitrogen available, the crop will die off prematurely and fail to achieve its yield potential.

“It’s important not to over-estimate N levels in the crop, because in a mild autumn and winter, the plants will keep growing and the concentration of N in the tissue can be diluted.  This means that big crops of GAI 2 or more may only have 40kgs/N/ha, per unit of GAI.”

A foliar N spray at the end of flowering had been shown to lift yields in nine trials, said Dr Berry.

It had produced a 0.2t/ha yield response average, a figure which included an adjustment for a slight decrease in oil content.

The increased yield should be viewed as an addition to the yield increase potential of any granular nitrogen that had already been applied.

Foliar N would not be so beneficial if put on in temperatures above 18 degrees Centigrade, he warned.  Care should also be taken to avoid crop damage during the application process.

Sulphur deficiency had been a burgeoning problem in oilseed rape, since air pollution regulations came into force, said Dr Berry.

In late winter/early spring, most northern crops would respond to about 75-80kgs/ha of SO3.  The nutrient could be applied at the late green, or even the yellow bud stage in situations where there was only a slight sulphur deficiency.

Chris Martin, Agrovista’s northern technical manager, said findings since last November’s oilseed rape trials report had highlighted the benefits of using a loosening time for soil preparation, to encourage rooting.

He said the soil structure damage, which followed two years of bad weather, would continue to recue crop performance for several years to come on many farms in the region.

“We have trialled a wide range of establishment techniques.  The plants have looked similar above ground, but closer examination reveals poor rooting, where growth has hit a soil pan,” said Mr Martin.

“A positive effect has been seen on plots where fertiliser had been applied at drilling, another way of encouraging root development.”

Other trial findings since last autumn’s update included the conclusion that the number of seeds per linear metre was more important than seed rate.

He advised growers to aim for 15 seeds per linear metre, to avoid early completion within the rows.  A consistent yield response from precision drilling had been recorded across all UK trial sites. 


03 March 2014

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