Companion planting with OSR shows great potential

Article taken from the Agronomist & Arable Farmer

Growing companion plants alongside winter oilseed rape is one of several novel ideas being evaluated by Agrovista at its seven Growcrop Gold trail sites this year.

Sowing legumes with oilseed rape and allowing the two to grow together for a few months may not sound like an obvious way to boost crop performance.  But companion planting, as the technique is known, has shown great promise in trials in France, improving crop growth and offering weed and pest control benefits.

Agrovista technical manager Mark Hemmant is keen to see if companion planting, which was developed by French seed and plant health specialist Jouffray-Drillaud, can deliver similar paybacks this side of the Channel.

Initial results suggest a specialist legume mix will perform as well or better with the UK’s varieties and growing conditions.  “It’s early days, but our first findings suggest there’s tremendous potential for the technique,” says Mr Hemmant.

“There has also been a great deal of interest in it from our farmer customers, with potential nitrogen savings of up to 40kg per hectare and yield responses of around 0.5t/ha.”

During the autumn, the companion plant mix ‘mops up’ any nitrogen and other nutrients that would otherwise be lost, as well as helping with weed control and contributing to soil health, drainage and structure.

Once winter arrives, the legumes are killed by frosts or, if temperatures don’t fall low enough, by a herbicide.  Nitrogen is released back to the soil ready for the growing OSR crop to take it up in the spring.

CHOOSE CAREFULLY

The choice of companion plant species and varieties is critical.  The blend used in the Agrovista trials is made up of specific varieties of common and purple vetch (Nacre and Bingo) as well as specific variety of berseem clover, Tabor.  These were selected by the French company for their susceptibility to frost and their ability to release nitrogen at different rates over a period of time, rather than in one hit.

“A great deal of work has gone into selecting the varieties which combine the right growth characteristics, rooting depths and frost tolerance,” says Mr Hemmant.  “They also have to grow well with OSR, without impeding the crop’s establishment and early growth.”  The common vetch, Nacre, is relatively slow to establish, but then grows quickly and develops good ground cover, he notes.

“That means it can have a smothering effect on autumn-germinating weeds coming up between the rows.  It makes up almost half the mix.”  The red vetch, Bingo, has similar characteristics but is faster growing and releases its nitrogen a bit later.  It accounts for almost one third of the legume mix.

The third component, berseem clover, is an annual which originates from the Middle East.  It grows well on most soil types, even very heavy ones, and develops rapidly during the summer and autumn if conditions are favourable.

The legume seeds were sown at 20kg/ha at the Agrovista sites.  Three crop seed rates have been compared, with Agrovista’s recommended 28 seeds/m², or 15 seeds/m of row length, being one of those.

“We used a Great Plains Simba DTX one pass system with two seed boxes fitted,” explains Mr Hemmant.  “Seed pipes from the first box place the OSR behind the DD rings in line with the loosening legs at 55cm row spacing.  The companion plants were then broadcast between the rows from the second hopper.”  Pre- and post-winter crop emergence counts have shown no negative effects from the legume mix on crop establishment, he reports.

GROWTH IMPROVEMENT

“What has been interesting is that crop growth was improved – especially on the more difficult sites.  The legume mix seems to help produce bigger, stronger OSR plants, perhaps due to improvements in soil health and structure.”  Nitrogen capture was also recorded.  Although this varied from site to site, up to an extra 23-29kg/ha of nitrogen was captured, the equivalent of 40-50kg/ha of bagged nitrogen.

“This is an exciting find,” he says.  “The legumes do nodulate but aren’t there long enough to fix nitrogen.  Their biomass releases nitrogen back to the crop, rather than it being wasted.”

This suggest that nitrogen applications could be reduced with companion planting, he adds.  “We’ll be doing more work on this.”

A surprise to Mr Hemmant was the positive effect at later-sown sites.  “Where weather conditions and slug populations were against us, there was a very noticeable difference between the straight crop plots and those with companion plants.”  The effects of slug grazing may have been diluted in the latter, he surmises.  In addition, the better soil health and companion planting may have helped.

Flea beetle numbers are also lower where companion plants are growing.  In France, where the technique is used on over 2,000ha, growers have reported using one less insecticide per crop.

Quite why is not clear – visual disturbance, a barrier effect or repellent properties have all been suggested in France, where flea beetle numbers halved to just 5-10 pests per plant.  Weed control with herbicides can still be carried out, but some alterations are needed to ensure that the legume mix survives, he advises.

“There’s further work being done on this.  We’re confident most graminicides can be used.  There are new OSR herbicides coming onto the market and developments such as Clearfield to be aware of.  So take advice before applying herbicides.”

The specialist legume mix is available from Agrovista for around £65/ha.  “It’s an additional cost, but there are considerable benefits,” Mr Hemmant concludes.  “The yield boost in France has been in the region of 0.3t/ha, and there can be savings in fertiliser and agrochemical inputs too.”

 

03 February 2014

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