Companion planting boost rape yields

Article taken from the FarmBusiness

Planting companion crops in with oilseed rape can increase yields and improve crop establishment, according to Agrovista technical manager Chris Martin.  Speaking at the CropTec event last month, he reported that UK trials based on experience gained by French growers showed that growing a mix of two vetches and Burseem clover offered significant benefits.

Yield improvements in the order of 0.3-0.4 tonnes per hectare were found, but significantly more where conventional crop establishment had been difficult.

The technique originated in France due to very strict regulation on nitrogen application and use which led to research on growing legumes as a nitrogen source for the crop.  The current work has concentrated on ‘mopping up’ available nitrogen in the autumn in order to make it available to the growing crop in the spring of the following year.  The companion crops establish rapidly, taking up N that would otherwise be lost by leaching or denitrification, but are then killed off – by frost in France, but by suitable herbicides in the UK – to rot down and release it again later.

Early results showed the technique was effective, with up to the equivalent of 40kg/ha of additional N stored in the combined biomass in the autumn.  On breakdown in the spring much of that was released, and a significantly higher amount of N would have had to be added to the crop to give an equivalent boost.  The system was also observed to have stored and released potash.

The UK trials were conducted on a farm scale, with continuing work on more than 100 sites with plots of up to 40ha.  An initial fining, in the difficult working condition of autumn 2012, was that crops planted with companions had significantly better establishment, something Mr Martin put down to reduce predation by slugs and other pests.

“One possible reason is that there was simply more biomass, which diluted the damage to the rape.  Another is that, in the organic world, there is a theory that a slug will get fuller quicker if it has a more varied diet; and a third idea, from a slug pellet manufacturer, is that some vetches are actually repulsive to slugs, and may be keeping them away from the crop plants.”

Anecdotal, but unconfirmed, evidence from growers suggested that pigeon and rabbit activity were reduced in the trial areas.

French experience, where seed treatment against flea beetle is not as common, indicated that predation by that pest appeared to have been reduce in accompanied crops, with many growers able to omit at least one autumn control spray.  Mr Martin suggested that the property might be beneficial in the UK as seed treatment products were withdrawn.

Improved Rhizosphere

Experience showed that soil structure benefited by the deep penetration of the roots of the companions, and that ‘lazy’ oilseed roots took advantage of that penetration to go deeper themselves.  It also appeared that there were general improvements in the rhizosphere – the soil and root structure at the base of the plant.  Soil aggregation improved, and French experience suggested that there were further benefits in terms of microbial balance and fungal and parasite numbers.

“There is something dramatic happening here that we need to explore further,” Mr Martin said.  He admitted there were still problems to be solved before the technique could achieve wide application.  Crop competition was an issue, as was weed control and the establishment of the companion crops.

The French have partly solved the competition issue by the choice of companions: the first to establish is the clover, a tall, slim plant which does not compete in the early stages.  By the time the ground-covering vetches come through, the rape is established and away from the competition.  Work is now being done to investigate whether this will hold true in UK conditions.

The herbicide problem has not yet been solved, but trials are under way to find effective herbicides against problem weeds that do not immediately wipe out the companions.


22 November 2013

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