Recycled phosphorus could be element of food security


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Newly published Manitoba research into the merits of recycled phosphorus could help reframe the multi-faceted debate around how farmers can sustainably feed the crops that produce our food.

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Newly published Manitoba research into the merits of recycled phosphorus could help reframe the multi-faceted debate around how farmers can sustainably feed the crops that produce our food.

The notion of recycling phosphorus is still fairly foreign in modern agriculture, but it’s gaining new traction as we come to grips with our Jekyll-and-Hyde relationship with this vital nutrient. On one hand phosphorus is contaminating our waterways and creating expensive wastewater treatment issues for the City of Winnipeg.

On the other, it is a non-renewable resource that we can’t afford to be treating as waste. Known phosphate rock reserves, none of which are located in Canada, are expected to be depleted within the next 140 years. What’s more, because Canadian farmers export most of what they grow, they are continuously drawing down the phosphorus banked in their soils.

The problem is particularly acute for organic farmers, who were the focus for a research team from the University of Manitoba. They can’t use the commercially produced fertilizer products, so unless they have local access to manure, they risk running their soils out of phosphorus.

The University of Manitoba research team set out to compare the performance of three forms of recycled phosphorus: struvite, which is a mineral pulled from municipal wastewater; frass, which is the castings by black soldier fly larvae fed household food waste; and anaerobic digestate, which is anaerobically composted food waste.

In a nutshell, their research showed these alternative products performed well, measured by plant uptake and the yield response. The frass and anaerobic digestate performed equally well as conventional products such as mono-ammonium phosphate (MAP).

It’s about more than productivity. If phosphorus is recycled into these forms, it doesn’t make its way into waterways and contribute to lake-killing eutrophication.

But until now there hasn’t been a lot of information made available to growers about how well these forms of fertilizer perform.

“This data for the Prairies has really provided a sound record for what responses people might expect,” said Martin Entz, who worked with Jessica Nicksy and Brian Amiro on the project.

Knowing these options work is helpful, and some organic farmers are already employing them. However, there are still barriers to their widespread use, not the least of which are the availability of supply, plus the cost and unease about using struvite derived from human waste.

Canadian organic standards currently allow the use of struvite from animal waste but not human. Entz said he expects that rule to be revisited as European countries move to allow its inclusion.

Even so, using struvite derived from human waste produced in Canada would only support a fraction of the farmland in this country that needs phosphorus, and the costs of creating it would currently be prohibitive. Where it does make sense is the organic sector, Entz said. Organic farmers receive a higher price for their production, which helps compensate for their extra costs of production and lower yields.

“Right now, organic agriculture occupies two per cent (of Canadian farmland). We could double that land base and we’d have lots of phosphorus to fertilize all those crops,” he said. “And so we would be running a sustainable — at least in terms of phosphorus — system.”

Research such as this sheds new light on a host of issues related to how agriculture will continue to support human life on the planet.

Firstly, it highlights the need to move toward circular management of resources, especially the non-renewable ones. We can’t afford to continue flushing phosphorus out to sea.

Secondly, it demonstrates there are viable options emerging, although cost and availability remain factors limiting uptake in conventional agriculture. With some farm groups alleging collusion and calling for an inquiry into why fertilizer prices have spiked well above what supply and demand fundamentals justify, having access to alternative sources becomes increasingly important for farmers.

Thirdly, it adds context to how different systems contribute to global food security. Critics have long argued that because organic systems typically produce lower yields, it will never be able to feed the world. Maybe not. But at the rate we’re going, conventional agriculture won’t be able to do the job either.

Laura Rance is vice-president of content for Glacier FarmMedia. She can be reached at

Laura Rance

Laura Rance

Laura Rance is editorial director at Farm Business Communications.

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