Green plants produce carbohydrates and oxygen out of CO2, using sunlight. Human beings and animals do exactly the opposite: they ‘burn’ carbohydrates with oxygen, releasing energy and exhaling CO2. Combine these two processes, as they occur together in nature, and you instantly have the ultimate circular economy, driven by solar energy! Is our current agriculture therefore circular by nature, or does it still require some additional actions on our part?
Guano, dried poop from seabirds or bats, can be mined on small islands like this one, just off the Peruvian coast. It makes an excellent phosphate fertilizer (Photo © Sander de Vries).
“Plants are the future. They absorb more CO2 than they emit. They only need a bit of sunshine and a drop of water to give us something very beautiful”. That’s how a recent TV commercial for a well-known Dutch margarine brand starts. If only it were that simple! At least three things were overlooked: plants also need minerals and land, and modern cropping systems also consume energy. These very things make turning agriculture circular quite a challenge. In this first blog of a series of three, we’ll discuss some problems and possible solutions in relation to the first-mentioned production factor: minerals.
Before using terms like ‘circular’ or the ‘circular economy’, we should clearly define what we’re exactly meaning by that. Let’s not make things more difficult than they are: Bob the Builder’s famous slogan “Reduce, Reuse, Recycle” constitutes an excellent summary. In a circular economy, we should not only recycle things when they are discarded but, first of all, consume less and try to keep using the same things for a longer time.
Back to agriculture. Crop growth requires some 17 different kinds of minerals, each having their own unique functions within the plant. Nature supplies them through weathering processes in the soil, through atmospheric deposition with rain and dust, and with surface and groundwater. On poor soils, agricultural productivity is often low due to naturally limited mineral supplies. That is why around 1850 the Netherlands, pressurized by rapid population growth and stagnating agricultural productivity, started importing so-called ‘guano’ from South America; phosphate- and nitrogen-rich poop of seabirds or bats. By importing guano and, later, other types of fertilizers, the limitations of natural nutrient cycles and supplies were gradually overcome. Eventually, the situation in the Netherlands was turned completely upside down! Not the availability of manure and minerals limits our current agricultural production, but the maximum volume of manure that the Netherlands can still cope with! Our gargantuan herds can only produce so much manure because the traditional land-related agriculture has been abandoned, by and large. Less than half the animal feed is grown on Dutch soils these days (source: Nevedi, 2017). Enormous volumes of soy and cereals are imported from the Americas and from other European countries. These ingredients contain minerals that eventually end up in animal manure, and the environment, in the Netherlands. Let’s have a closer look at two of the elements that are imported in large quantities and have a substantial impact on the environment: nitrogen and phosphorus.
Nitrogen: available in infinite quantities?
Most nitrogen on Earth is present in our atmosphere, in the form of the relatively inert gas N2. Almost 80% of the air that we breathe consists of it! In fertilizer manufacturing plants, N2 is forced to react with hydrogen gas (H2), obtained from natural gas, under high temperature and pressure. This so-called Haber-Bosch process, which requires large amounts of energy, yields synthetic ammonia (NH3). Ammonia is then used to produce nitrogen fertilizer for agricultural applications. However, only about 50% of the nitrogen applied in agriculture is taken up by crops, globally; the other half is lost! These nitrogen losses negatively affect the quality of surface and groundwater and of the environment in general. Although all nitrogen may eventually return to the atmosphere via the natural nitrogen cycle, there are major challenges with respect to nitrogen use in agriculture and the circular economy. A process that accounts for 1-2% of the global energy consumption and 3-5% of the natural gas consumption can hardly be characterized as circular… and then we’re not mentioning the accompanying greenhouse gas emissions yet!
Phosphorus: a finite resource
Imported animal feed in the Netherlands not only contains nitrogen, but also phosphorus. Much similar to nitrogen, it easily ends up in the environment via animal manure. However, phosphorus, once lost, cannot easily be regained. It is a fossil raw material, which is extracted in vast open-pit mines; the largest known reserves can be found in Morocco and the Western Sahara. Whereas nitrogen may eventually return to the atmosphere, from where it can be extracted anew, it may take millions of years for phosphorus to be sequestered again in concentrated form. Moreover, due to the ever-growing demand for agricultural products, the demand for phosphorus fertilizers has steeply increased over the past decades. The end of the known reserves is approaching slowly but steadily; scientists estimate that the supplies are sufficient some for only 50 to about 200 years. For that reason, but also because of the environmental damage of open-pit mining and the agricultural losses to the environment, it is urgent to find a more circular way of dealing with phosphorus in agriculture.
Open-pit phosphate mine in Togo, West Africa. (Photo: A. Pugachevsky. Original image shown. Image license).
Back to Bob the Builder’s powerful slogan; what could be reduced, and how, with respect to minerals in (Dutch) agriculture? Firstly, it is often possible to reduce mineral applications whilst maintaining crop yields at their current levels. Aided by sound fertilization advice based on crop and soil analyses, mineral losses can be reduced, enabling crops to take up some 70% of the applied nitrogen instead of 50%, for instance. New innovations, such as mobile aps, drones, smart sensors and satellite imaging may also assist here. Secondly: could Dutch agriculture reduce its productivity and import of feedstuffs, reverting to a more traditional land-related brand of agriculture? Shift from production of bulk goods to products with added quality and ecological value? That is a politically sensitive topic and the question is whether it would really help. The Dutch produce mostly for export after all, and the averted production might just be displaced to other regions. Reducing productivity would surely have environmental benefits though. When agricultural production exceeds 75% of the theoretical potential, as in the Netherlands, emissions to the environment start to increase more than linearly. Partly due to its nitrogen and phosphorus problems, the Netherlands has the second lowest biodiversity in the European Union. Thirdly: a lot of energy could be saved by fixing nitrogen from the atmosphere with so-called legume crops, instead of with the Haber-Bosch process. Legume crops such as beans, peas, lentils and clovers live in symbiosis with Rhizobium bacteria, that fix nitrogen from the air for them, in exchange for some carbohydrates. The legume crops turn the nitrogen into proteins hence make a great source of food and feed and can be used as a green manure for other crops; practices that have long been common ground in organic agriculture.
Legume crops such as red clover (Trifolium pratense) live in symbiosis with Rhizobium bacteria, that fix nitrogen for them from the air. The clover then turns the nitrogen into proteins that make excellent animal feed or green manure (Photo © Sander de Vries).
Fortunately, a lot of things are being reused in agriculture already: first of all, half of the ingredients used in Dutch animal feeds are residues from the food industry (source: Nevedi, 2017)! A relevant question with respect to mineral cycling remains of course whether the raw materials in the food industry come from the Netherlands or from elsewhere. Secondly, crop residues, particularly protein-rich ones from legume crops, are used as animal feed. The animal manure can then be used again as a fertilizer. Thirdly, fibre-rich crop residues such as straw can be used to produce bioplastics and biofuels. Yet, it is wiser to retain them as a soil ameliorant if the soil requires it.
With the import of animal feed ingredients such as soy and cereals into the Netherlands, large quantities of minerals are imported too. These minerals eventually end up in animal manure and may accumulate in the environment. To close the global mineral cycles, some have suggested to ship the manure back, in supertankers! Nowadays, more realistic solutions are available however. By processing excess manure into dried granules, products are obtained that are more suitable for export. We can also recycle the phosphorus that we consume in our own food, by producing ‘struvite’ at sewage water treatment facilities: a high-quality phosphorus fertilizer. Recent research initiated by Sander de Vries of Kind of Green® has shown that it may be economically profitable to export struvite from the Netherlands to West Africa, where there is a lack of affordable fertilizers. Another recent innovation is growing duckweed on the (diluted) liquid fraction of cow manure. The duckweed takes up minerals, particularly nitrogen, hence purifies the liquid. The duckweed itself, due its high protein content, makes an excellent replacement for imported soy! Technical information on this technology can be found in the report “Purifying Manure Effluents with Duckweed”. This report was produced in the context of the past Climate KIC project DUCKOFARM (Defusing Unwanted Climate change by Knowledgeable On FArm Refining of Manure), initiated by Sander de Vries of Kind of Green®.
Big bags of struvite, a high-quality circular phosphate fertilizer, produced at a sewage water treatment facility in the Netherlands (Photo © Sander de Vries)