Green fertiliser made from cow dung and chicken feathers could transform big agriculture

A raft of strategies is being trialled in Europe to turn nutrient-rich farm waste such as chicken feathers, cow dung and plant stalks into green fertiliser. Full of phosphorus and nitrogen, recycled products could help reduce intensive agriculture’s emissions and reliance on fertiliser imports.

European agriculture produces an abundance of high quality food, but also massive amounts of waste from crops and farm animals, including about 1.4 billion tonnes of manure each year.

Farm waste is bursting with nutrients, but these are often in complex organic molecules, which take time to break down into minerals for crop plants to use. Manure is voluminous, difficult to transport and usually generated far from crop fields. Consequently, farmers rely on chemical fertiliser that is often imported into Europe.

While the EU market for fertiliser is valued at between €20 – 25 billion per year, synthetic fertiliser accounts for 80% of products. The nitrogen is made by taking the chemical from the air and using energy from fossil fuels to convert it into ammonium salts that plants easily consume. Phosphorous, the other main ingredient in chemical fertiliser, is made from rocks mined mostly in Morocco, but also China and the US. 

Meanwhile, nutrients spread onto farmland can leach into rivers and lakes, causing algal blooms and fish deaths, or evaporate as greenhouse gases. 

‘We have too many nutrients flowing around in Europe, causing environmental problems,’ said Professor Erik Meers, an environmental chemist at Ghent University in Belgium. ‘We also have an increasing amount of chemical fertiliser, nitrogen and phosphate, being used.’ 

An estimated 13.6 million tonnes of nitrogen and 1.8 million tonnes of phosphorus enter European agriculture each year through fertiliser, but also the crops used in animal feed.

‘We are not recycling all the nutrients that we could re-use,’ said Dr Victor Riau Arenas, a scientist at the Institute of Agrifood Research and Technology in Catalonia, Spain. He leads a project called Circular Agronomics that aims to boost nutrient recycling in the agricultural food chain and to help reduce emissions. ‘We aim to convert the linear chain we have today into a circular chain by recycling nutrients.’

With new EU legislation in June 2019 making it easier to sell fertilising products made from recycled materials, Dr Riau and Prof. Meers are among the researchers now working to extract pure nutrients from organic waste to produce sustainable bagged fertiliser.

‘We have these vast flows of nitrogen and phosphorous coming towards Europe in the form of imported chemical fertiliser and in the form of imported animal feeds.’

Prof. Erik Meers, Ghent University, Belgium

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