HomeResourcesCircular economyWhy we should care more about the environmental impact of nutrients

Why we should care more about the environmental impact of nutrients

crop-spraying_chafer-machinery_flickrBack in 2007, Green Alliance examined the challenges and opportunities for the more sustainable use of nutrients, chiefly nitrogen and phosphorus, in the UK. It recommended a suite of policy principles to make a more circular system a reality.

Little has happened since in the UK. But last month I was asked to present Green Alliance’s policy principles to a conference of Nordic countries in Malmo, and to discuss how to take the agenda forward. I discovered that the ideas remain relevant and useful. 

Green Alliance has taken the lead in arguing that a circular economy is more resilient.  Such a strategy can insulate from the global price and political volatility of commodities, as well as giving market value to what would otherwise be a waste product and a cost.  But nutrients are a contested dimension of this argument.

Phosphorous is a critical nutrient at risk
Consider phosphorous.  For an element so crucial to life on Earth, it is surprisingly overlooked. Phosphorous cycles through natural systems, but food production on the scale we have today would be impossible if we didn’t add extra to soils as fertiliser. Of the three key plant nutrients: nitrogen, phosphorous and potassium, phosphorous is the most critical, since it is a major limiting factor to plant growth. It is also potentially the resource most at risk.

On the one hand, there’s talk of ‘Peak P’. Production of the high grade rock form of phosphorous is concentrated in just a handful of countries, and it is estimated that three quarters of the remaining reserve is in Morocco.  Much of that presently travels through an above ground pipeline.  Unsurprising then that security of supply is a talking point.  But whether there is genuine scarcity depends on who you ask; some estimates put ‘Peak P’ at just 15 years away, others at several hundred.

Nitrogen will never be scarce thanks to the Haber Bosch process, which enables us to make nitrogen out of thin air, but at considerable energy cost: it consumes around three to five per cent of the world’s annual natural gas output.

Closing the loop makes sense
So, when both nitrogen and phosphorous are abundant in organic wastes of all kinds, including animal slurry, compost, sewage sludge and residues from anaerobic digestion, closing the loop to reuse them should be attractive.  After all, slurry, compost and sewage are what mankind relied on to replenish the fields before mining and manufacturing took over not much more than 100 years ago.

On the other hand, it’s argued, the scale of demand, and the cost and disruption of coming up with new systems, mean we should focus on improving existing processes. It is relatively expensive to extract high quality, easily transportable fertiliser from a wet organic mess. In any case, there wouldn’t be enough to enable us to feed the populations we have now, let alone the population we’ll have in thirty years’ time.  It may be possible to get phosphorous from lower grade rock, and make nitrogen production more energy efficient.

Why are Nordic countries interested now?
Nordic countries are looking at the problem from a wider perspective.  The environmental consequences of current fertiliser use are severe, and a significant cost to the economy. Swedish scientist Johan Rockstrom, famous for his spider diagram showing the ‘planetary boundaries’ , clearly identifies nitrogen and phosphorous loading as two of three areas where we are already outside safe limits.   Around the world, we are paying for and using more fertiliser than is needed or the land can handle, which can result in catastrophic and costly water pollution.   The Baltic is one the most nutrient-polluted seas in the world, thanks to the drainage from agricultural land that flows into it, and it regularly suffers from toxic algal blooms that cover thousands of kilometres of water.

Here in the UK, as Green Alliance recently pointed out, water companies currently spend hundreds of thousands of pounds a year taking excess nutrients out of water.  The commonly used process for doing this results in an unusable waste and, in only a handful of cases, is it economic to use an alternative means (like struvite production) to recoup the nutrients in a usable form. The UK returns more sewage sludge to land than many other countries, which closes the loop to some extent, and WRAP has done great work to make the residues of anaerobic digestion more attractive as a source of nutrients.  However, the holy grail is to have a flexible, tradable product that customers see as a valid replacement for the primary resource.

Principles for action
What do we need to do about it?  Not wasting  resources would be a good start.  Fertiliser production and application involves loss at many stages, which could be remedied.  At an even bigger scale, globally, we waste around a third of all food produced.  It is senseless to fret about the availability of inputs at the same time as losing such a staggering proportion of the output.

But we can go further. A set of policy principles for closing the loop, as Green Alliance set out in its 2007 report, involves aiming for much more precise application of nutrients, based on recognising soils as a crucial resource in themselves, as well as a better understanding of what they need.  Some UK water companies are already funding agronomists to build that enhanced understanding, to protect water from nutrient pollution at the very beginning of its journey to our taps.

It also means accepting that phosphorous is a finite resource.  Even if lower grade reserves are exploitable, we have to be sure we won’t face problems of ever greater environmental disruption.  Given that secondary nutrients are presently a waste and a cost, it makes sense to prioritise recapturing them over the mining of new sources, even if they make up just part of overall demand.  Any policy instrument that required or encouraged the use of the secondary sources would have no trouble creating a market.

Nordic countries are taking forward these ideas with characteristic thoroughness. The Nordic Council of Ministers is supporting a network that will meet again next March, to identify the challenges and work towards a common strategy. The UK’s next step should be to re-evaluate our land, water and waste management as one set of related problems and consider what opportunities are offered by post-CAP policy to close the loop.

[Image courtesy of Chafer Machinery from Flickr Creative Commons]
Written by

Green Alliance Associate, Chair of WRAP and independent board member of the Consumer Council for Water. @JulieEHill