Field margins 'help control weed dispersal'

Tractor in a field (Getty Images) It had been thought that field margins were a reservoir for weeds

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Grass strips on field edges do not result in more weeds growing among crops, research has shown.

Previously, it was argued that the "set aside" land could act as a reservoir for weeds that potentially result in the plants being dispersed into fields.

Field margins are one of the key European agri-environmental measures, and are considered to help maintain biodiversity in farm landscapes.

The findings will be published in the journal Weed Research.

"Sown grass strips (SGS) have been widely established on field margins... because of their expected environmental benefits," the team of French researchers said.

"Semi-natural habitats have been lost with field enlargements or have been degraded in terms of flora diversity by adjacent intensive agricultural practices.

"Consequently, different agri-environmental plans have been initiated to protect water resources or enhance biodiversity in arable landscapes."

However, previous studies had raised the concern that field margins, which allow some of the land to remain unplanted, could act as an extended reservoir for species deemed to be weeds and increase their dispersal into the crop fields.

The team from the French National Institute for Agricultural Research (INRA) surveyed the composition of plant species within five-metre SGS in 10 fields and found the set-aside land resulted in a "sharp decrease" in the number of weeds encroaching into the cropped area.

Co-author Bruno Chauvel said the findings were surprising on some levels.

"In the 'best' scenario, it could be very interesting to create new habitats within the agricultural landscape where 'natural' plants could be present," he told BBC News.

However, he added: "We know that a large number of [weed species] require the disruption of soil tillage to survive - favouring their germination."

But as a number of the species deemed to be weeds only have small seeds and limited energy reserves, they struggle to compete against grass species that are planted by the farmers as part of the SGS system.

"Most of the species are not able to germinate on the surface of the soil; as there is no tillage, seeds are more sensitive to predation (from birds etc) and abiotic stress (lack of water, frost etc)," Dr Chauvel explained.

"Of course, there are exceptions - such as wind dispersed species - but even strongly invasive species disappear in [grass] cover."

He added that longer studies were required in order to measure the benefits of SGSs to the biodiversity richness of an area.

Claire Robinson, countryside adviser for the National Farmers' Union, welcomed the research, adding that developments in land stewardship research was an important tool in helping farmers.

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