Start by unpacking circular agriculture

WUR researchers Pieter de Wolf and Wijnand Sukkel are standing on an industrial site in Amersfoort, peering through a glass window in a stainless-steel tower. Inside, an artificial tornado is producing tiny granules. This is where the Vallei and Veluwe Waterboard are processing wastewater to extract struvite, a phosphate fertiliser with a small amount of magnesium. A short distance away, bulk bags of finished granules are lined up, ready for transport. “This here is a great example of closing the loop. Because our role as humans in wasting this resource has long been overlooked,” says De Wolf.

Should you grow animal feed on expensive Dutch agricultural land?

Phosphate is a finite resource and in this way some of it can be recycled. In Amersfoort, 30-40% of phosphate is being successfully retrieved from wastewater. It’s a first step. If the technology develops further, 60-80% should eventually be achievable, according to the water board’s process technician. But unfortunately it’s not commercially viable, he adds. Sukkel agrees: “Minerals are just too cheap for that. You’d have to work with unprocessed sludge. That would allow you to also extract organic materials and micronutrients. But unfortunately there are too many impurities in it, like heavy metals and chemical residues.” One solution, he says, could be to separate waste flows at an earlier stage, so that urine and faeces are separated from ‘grey’ wastewater. This is being trialled in several residential neighbourhoods in the Netherlands.

Hidden fertiliser use

Within the field of agricultural research, circular agriculture has traditionally been synonymous with linkages between the plant and animal sectors. It may be coincidental, but the first project that De Wolf and Sukkel ever worked on together at WUR was a project on Mixed Farming Systems. “So in that sense the theme itself is circular,” says De Wolf with a grin. “But the issue has developed into a broader one over the years. Too broad, in fact, because what you see now is that circular agriculture seems to cover everything from biodiversity to the climate. That can rapidly muddy the waters of the debate. So in that sense the Ministry of Agriculture, Nature and Food Safety needs to flesh out its vision of circular agriculture a bit more. It needs to be fully unpacked. What is the problem you want to solve? Articulate that.”

According to the researchers, many issues are still closely linked to agricultural specialisation and the decoupling of land and livestock. Agriculture is simply less circular than it was in the past. “Arable farming and livestock farming could be more closely intertwined,” according to Sukkel. “But that does mean keeping an eye on mineral and carbon cycles. For example, we talk about wanting to swap artificial fertiliser for animal fertiliser, but of course the use of artificial fertiliser remains embedded in that. We import it through Rotterdam with the livestock feed. Under the circular model, any fertiliser you generate here would be put back into the system, so that minerals and carbon are returned to the land they came from.”

So do we want to maximise circularity within the borders of the Netherlands? Or should we look at this on a European scale, because we export a lot to the countries around us? Photo: Ruud Ploeg

That immediately begs the question: at what scale are you scrutinising the cycle? “In crude terms, the Netherlands at the moment is a large pump in the global nutrient cycle,” says de Wolf. “We import a lot of nutrients with livestock feed, and less than half of it ends up in products. The rest ends up as manure or is lost. So do we want to maximise circularity within the borders of the Netherlands? Or should we look at this on a European scale, because we export a lot to the countries around us? Those are political choices, because circular processes don’t happen spontaneously.”

Beet leaves

Economic realities limit the opportunities for Dutch farmers to close local loops, or to contribute to the circular economy. That’s another issue that the researchers want to emphasise. “For a long time it was all about scaling up, specialising and being efficient, to drive production costs down as far as possible. You can’t reverse that in an instant. So there are a lot of areas where efforts to close the loop are thwarted by the prevailing economic model,” says De Wolf. As far as he’s concerned, people are a bit too glib about using byproducts as raw materials in a circular model. Random interventions somewhere in the cycle will have immediate technical and economic consequences, and they need careful consideration, he says. “If you start using byproducts in a different way, that can fit really well in a circular model, but you do need to ask yourself what the consequences will be. Harvesting beet leaves to use as livestock feed is something that has often been researched in the past, but has always turned out to be too expensive. It’s a bulky, wet, perishable product. Harvesting it also comes at the expense of soil fertility, because you’re removing organic material and nutrients and you have to use heavy equipment on the land even more often.”

Agriculture will never be a fully closed loop

As an agroecologist, Sukkel is also focusing on the soil issue. “Soil is often forgotten. Proponents of biobased approaches are keen on agricultural biomass. But removing so-called byproducts from arable farming comes at a price too. They’re necessary for feeding soil life and keep the land in a healthy condition.”

Fertiliser diversity

De Wolf proposes that we approach this from the opposite direction. “How much can the Dutch Delta handle? What do we want from our land? Concentration has made us quite efficient, but that comes with environmental drawbacks. How much cattle can our agricultural land feed, and how many animals do we need to make use of our byproducts? Should you grow animal feed on expensive Dutch agricultural land, or focus more on what people can immediately eat? What choices do we want to make?”

The researchers are clear that animals play a role in circular agriculture. “Animals are very good at turning byproducts and grass into high-quality nutrients,” says Sukkel. “That means they play an important role in sustainable farming systems. You can then address the question of how many animals. There’s a common argument that animals are important for fertiliser, because they can replace artificial fertiliser. But those nutrients always have to come from somewhere. You’re just adding another stage of transformation. If you look at the nutrient cycle on its own, then including animals in the production systems introduces more losses than you would otherwise have.”

Even so, they see no justification for reducing livestock by half, as was proposed by the D66 politician Tjeerd de Groot. “No one said it needed to be 50 per cent. But I wouldn’t be surprised if optimising circular agriculture at the national or European scale gradually led to a reduction of livestock. Manure processing can also be part of the solution when it comes to making better use of minerals. But every step requires energy. So you should absolutely use unprocessed manure wherever you can. Having said that, there will be new types of manure that can replace chemical fertiliser to some extent. More fertiliser diversity, in other words, including human manure.”

‘Less leaky’

The researchers have noticed that the term ‘circular agriculture’ can sometimes cause confusion. “Agriculture will never be a fully closed loop, because there are always going to be unavoidable losses. This is particularly true for nitrogen. Nitrogen nutrients is often volatile and easily lost, which means they end up in places like nature reserves where they are harmful. Or they break down into elemental nitrogen (N2). It then takes a lot of energy to transform it into nitrogen that plants can use. Even if you maximise your circularity, something always needs to be added to the system. So what you’re actually trying to do is to make the cycle less leaky,” says Sukkel. He estimates that the maximum nitrogen efficiency would be around 75 per cent.

Farm of the Future

Farm of the Future is one of the places that will generate more insight into this. It’s where WUR Field Crops performs its system comparisons, and where circular agriculture will be researched in practice. As well as making technical comparisons, the research will consider the economic aspects. “Something might be a perfect fit for the circular model, but if it costs three times as much as the existing method, it’s just not going to happen. That’s why we consider the economic aspects from the very start,” says De Wolf.

The project will also consider the balance of energy use. If you start from the point of local loops, you can find that new approaches emerge. “Why would you start by bringing all your sugar beet to Hoogkerk? You’re moving a lot of water, pulp and tare soil that you could just as well leave where it is. An initial small-scale beet processing stage could save a lot of transportation and create new local loops.”

The role that animals will play in Lelystad is still under discussion. “It’s interesting to look at what you can do without animals too,” says Sukkel. “You can mow and compost grass clover rather than having it go through an animal first. What we really want to do is demonstrate a number of options and shed some light on the whole cycle.”

The human leaks from the cycle are not being left out either. “Look at the human waste streams that come out of cities like Almere and Lelystad, or the Walibi Flevo amusement park,” says De Wolf. “They’re really interesting, because there’s such a concentration of people and therefore of minerals. We’re keen to work on that at the Farm of the Future.”