Green manures are set for a boost in popularity, according to organic growing charity Garden Organic, as the cost of nitrogen fertilisers rockets and pressure to reduce leaching into ground water mounts.

The price of fossil-fuel dependent, synthetic nitrogen fertilisers has risen by 15 per cent in the UK over the last three years as the cost of oil as soared, and growers will need to find other ways to fertilise their soil, according to Garden Organic’s research team.

New legislation governing nitrate pollution is also building the pressure on growers to prevent nitrates leaching into ground water, and therefore better fertility building solutions are needed for both conventional and organic growers.

The Midlands-based charity has been researching and promoting organic growing for nearly 50 years, and has conducted several detailed studies of green manures over the last 15 years.

Dr Francis Rayns, soil scientist at Garden Organic, carried out a four-year field scale trial funded by Defra. He said: “We found that growing grazing rye over the winter reduced leaching of nitrogren by up to 97 per cent, compared to leaving the soil bare. This proves that growing a green manure is one of the best ways to hold nitrogen in the soil, reducing the need for fertilisers.”

The environmental benefits of green manure and its ability to suppress weeds, reduce soil pests and create a habitat for predatory insects are added advantages, according to Dr Rayns.

Garden Organic has also been working closely with growers across the country, as part of a new project funded by Defra on fertility management strategies in organic arable and vegetable production. Red and white clover are currently the most widely used green manures to build soil fertility, and the charity is hoping its research into other species will help growers across the country. A number of on-farm field trials are being held across the UK, including sites in Sussex, Cambridgeshire, Lancashire and Herefordshire.

The charity held a one-day event last month at Warwick HRI in Wellesbourne, dedicated to managing soil fertility, for over 60 growers. A second event will be held next year.

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