A project in Mid Wales has been trialling how foliage harvested from trees can be used as fertiliser. Crops need nitrogen for good yields, but nitrogen fertilisers are expensive and can be lost to the environment as pollutants, especially in warm weather and in bouts of high rainfall.
The Perennial Green Manures project has explored the idea of growing areas of trees, shrubs and other long-lived plants in what they have termed ‘bioservice areas’. These areas can help farm productivity by providing shelter and habitat reserves increasing the environmental resilience of the farm, but crucially they also produce nitrogen. By including nitrogen-fixing plants, such as clovers, broom bushes and alder trees, they can build up nitrogen in the green leaves, which are harvested and added as an organic fertiliser to soil.
It’s a similar idea to the traditional practice of growing nitrogen-fixing green manures on cropland, which are cultivated in to fertilise soil. But instead of growing them on prime cropland, perennial green manures can be grown on less productive parts of the farm, and harvested and added as and when needed.
The project has been working with local growers who have been experimenting with the method. They added the leaves of perennial green manures, either fresh, dried or pelleted to fertilise their crops.
Emma Maxwell, grower at Ash and Elm Horticulture, said: “I think the pellets are a great idea. These could be produced on scale at a dedicated coppice woodland and sold as a fertiliser boost.”
Subsidies in Wales, Scotland and England are all moving towards payments for farmers who increase tree cover on farms. Farmers are concerned about the loss of productivity that can result from giving land over to woodland. They have been out in force earlier this year, often in their tractors in town centres, and outside the Houses of Parliament, protesting against a number of measures including changes to government subsidies.
The Perennial Green Manures project, part of Ecodyfi based in Machynlleth, hopes that this idea might be explored further so that farmers can benefit from planting trees, not just in subsidies, but by increasing the farm productivity.
The report outlines results of research to date, and give ideas on the next steps for anyone interested in Perennial Green Manures.
Insights from the Perennial Green Manures project: an innovative approach to fertilising cropland
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Download the report summary in English here
