Trials show the value of OSR companion plants

Article taken from The Northern Farmer, written by Wendy Short

Agrovista’s Chris Martin gave growers an update on oilseed rape performance from the company’s Growcrop Gold trials at Croft, near Darlington.

He said the prolonged wet spell during and after the 2012 oilseed rape drilling season made it impossible for the trial plot seedbeds to be consolidated after sowing.

A range of drilling machinery was evaluated, including the Vaderstad Topdown and Biodrill, the Great Plains DTX and the Amazone ED precision drill.

Under these conditions, the Amazone drill had produced the best results due to its press wheel, which firms the soil behind individual coulters.  This machine topped the yield league.

Mr Martin said: “There was no opportunity for a post-drilling roll until the three to four leaf stage of the OSR.  The cold, wet soils also increased slug pressure and plant populations were low in general.

“However, despite disappointing establishment rates across the board, all the drilling techniques managed to produce very respectable yields of four tonnes-plus per hectare, as long as the crop had produced a minimum of five, evenly-spaced plants per square metre by harvest time.

“This is highly consistent with results from previous years and from other sites around the UK.”

Establishment was significantly improved where DAP (di-ammonium phosphate) 18:46:0 was applied at up to 165kgs/ha, in a band just below the seed.

This created a “grow bag” environment for the emerging oilseed rape plant.  DAP take-up was much greater when applied banded at planting, compared with an overall application at the early emergence stage.

The sowing of companion plants with oilseed rape also significantly improved establishment rates.  While relatively common in France, this practice is fairly new to the UK, but has been trialled extensively at the Agrovista Growcrop Gold sites.

Early results suggest that it has considerable potential for growers in this country.  Overall figures from Croft showed that an extra 38kg/ha of nitrogen was available to the oilseed rape in the spring on plots where it had been grown alongside companion plants.

“The reason this system has been such a success is because companion plants grown alongside the OSR in the autumn are essentially ‘harvesting the sun’,” said Mr Martin.  “They ‘mop up’ nutrients, such as nitrogen, which would otherwise be lost to leaching or de-nitrification over the winter.

“The companion plant species are specifically selected to be killed by frosts over winter.

“They also have a very low carbon to nitrogen ratio, so they will gradually release the nitrogen back to the crop in the spring, when it needs it.

“It is also believed that companion plants trap other key soil nutrients, as well as reducing pest damage, particularly by slugs and flea beetles.”

The mix of companion plants chosen for the trial work included common vetch, purple vetch and berseem clover.  They were sown with a Simba Great Plans one-pass system.  Oilseed rape from the first seed hopper was dropped behind the DD rings in 550mm rows.

For this technique, it was important to ensure that the pipes were placed immediately behind the legs, as well as into the groove left by the DD ring, he stressed.

Meanwhile, the companion plant seed was broadcast from the second hopper, to land between the rows of oilseed rape plants.

Mr Martin said: “The berseem clover, with its smaller seed size, was the first to emerge.  It has a more vertical growth habit, compared with the other companion plants.  This safeguarded the oilseed rape in the early stages, when it is most sensitive to competition.

“The vetch species, with their larger seed size and more prostrate growth pattern, emerged from the soil later on and filled in the gaps left between the rows.

“Pre-emergence and post-emergence counts had no negative effect on crop establishment.”

Where companion plants had been sown, there was a significant yield benefit from all three seed rates.

“The yield enhancement varied between 0.33t/hectare and 0.5t/hectare, with all the trials sites managing to produce a significant response,” said Mr Martin.

“The companion plants promoted oilseed rape rooting and growth without exception.  But we are still not sure whether this effect was due to the enhanced stimulation of soil microbes, or the ability of the companion plant roots to improve the soil structure, possibly through better drainage and aeration.”

Mr Martin pointed to an inescapable rise in the cost of oilseed rape seed in the future, as it was becoming increasing common to bind the seed with nutrients and fungicides.


10 January 2014

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