Cash in French-style cover
event, Les Culturales,
takes place only every
other year. In the years in
between ITCF, the national
cereals institute, runs a
series of themed field days.
Andrew Swallow reports
from this years programme
entitled Les Interculturales
– the intercrops
GROWING a cover crop between cash crops boosts yield and protects the environment, says the French cereals research and extension service, which is running a series of eight regional open days on the subject.
Whats more, if you are farming in France, such inter-cropping can earn the grower up to £60/ha (£24/acre) in countryside stewardship-type payments, explains the Institute Technique des Cereales et des Fourages.
"At the end of four or five years of intercropping your yields will be better," says Jean Paul Prevot who heads ITCFs Mons office in Frances northern Picardie region. The boost can be up to 10% in wheat, he says.
That claim is supported by work on chalk soil at Thibie in the Champagne region and on silty loam soil at Boigneville, just south of Paris.
Since 1995 the yields of all three main crops in a sugar beet, pea and wheat rotation at Thibie have been higher following an intercrop cover than without. At Boigneville pea and wheat yields have consistently benefited in a pea, wheat and spring barley rotation.
Improved soil structure and the release of nitrogen trapped by the cover crop that would otherwise have been leached away over winter probably account for the yield response, says Mr Prevot.
"You can trap up to 60kg/ha of nitrate with an intercrop, which is then released for following crops," he explains.
But across a total of 149 intercrop trials by ITCF in recent years there have been occasions when yields have suffered due to lack of water, nitrogen or reduced emergence in the following main crop, he points out.
Delayed destruction of the intercrop is a common cause of those problems. Weed control and pest pressures, such as slugs, must also be carefully considered when choosing which intercrop to use.
"There is no reason why you shouldnt produce a false seed-bed, spray off the weeds, then sow the intercrop. You must prioritise which is most important, controlling weeds or trapping nitrogen."
Couch or creeping thistle can be conveniently controlled with the glyphosate spray used to destroy the intercrop, he notes.
While it is possible to intercrop ahead of autumn sown crops, covering the ground over winter before spring crops is the priority, he stresses. "Lots of nitrogen is mineralised in the autumn. The risks of losing this are much higher before a spring crop."
Only a moderate amount of intercrop growth is needed to mop up the nitrogen and protect the soil from erosion and capping, he adds. Hence cover crops may be destroyed by spray, frost, or mechanical means as early as November and still have the desired effect.
Choosing a cover that is easily destroyed and will not become a weed in the rotation itself is important. Italian Ryegrass, for example, could be a risky cover in a cereal-based rotation.
Mr Prevots suggestion is broadcast mustard. "It is cheap, easy to sow, grows quickly and is sensitive to frost and mulches easily."
• Costs £0-24/ha.
• Traps up to 60kg/ha of N.
• Improves soil structure.
• Cuts erosion and leaching.
• Long-term yield gains
Under Frances equivalent of the countryside stewardship scheme, the "Contrat Territorial dExploitation" or CTE, growers earn £50-60/ha by sowing a non-leguminous cover crop before Sept 15 on soil that would otherwise be left bare over winter. Mustard, radish, phacelia, ryegrass and rye are all approved and up to 80kg/ha of nitrogen as slurry or FYM may be applied. Destruction must be after Nov 15 or even later in some regions. Subsequently soils must be analysed for nitrogen content and records kept. The "contrat" is a five-year commitment.