• Mark

The circular economy series

Updated: Dec 27, 2019

Feeding crops - to feed the world - to feed crops

Much of this debate revolves around the cost to the planet of sourcing, making and applying artificial fertilisers.

Issues such as

1. Depletion of the earth’s resource of Phosphates and Potash (Potassium)

2. Significant energy use from oil, coal and natural gas in manufacture of fertilisers

3. The amount of C02 produced in their manufacture

4. The inefficient use of applied fertilisers and the subsequent fatal nutrient enrichment of waterways.

5. Loss of soil structure and subsequent erosion by wind or water.

6. Loss of biome – the intricate web of micro flora and fauna within the soil.

The starting point as we know is that all plants and trees need nutrients to grow, same as for all life. The problem arises when we grow intensive fast turn-around agricultural crops that are removed from the soil every season and taken away for human and animals to feed on. That results in loss of nutrient for subsequent crops.

Fertiliser spreading
Photo: Agrex - Spreading inorganic nitrogen

Farmers already have a number of ways of restoring nutrient to soil.

1. Composted animal or even human waste as fertiliser

2. Undersowing the main crop with a nitrogen fixing legumes (Clover or vetch)

3. Mixing back the remains of plant tissue not harvested

4. Growing a break crop that is ploughed back into the soil or an animal rotation

5. Foliar or soil applied natural or artificial fertiliser

What do we mean by nutrients – what are they and what do they do? The most important macro nutrients are carbon, hydrogen and oxygen (which are available in water), nitrogen, phosphorus and potassium. Next in importance are calcium, magnesium & sulphur, and closely following them are elements such as iron, copper, zinc. After that there are the micro nutrients which would include things like boron, chlorine, manganese, molybdenum and nickel.

All of these nutrients are used to build chlorophyll, amino acids and proteins, growth hormones and skeletal tissue such as the xylem and phloem that transport water and nutrients through the plant stems, and the silicates and fibres that support structure.

Where do nutrients come from?

The most important nutrient to all growth, nitrogen, is available either naturally (78% of air is N) or inorganically by manufacture. Most nitrogen fertiliser is made by chemical manufacture of ammonium nitrate, which contains readily available nitrogen, which is then encased in pellets and spread on the fields to dissolve into the soil.

The main problem, and it is a big problem, is the energy consumption in the manufacturing process. It is huge and amounts to approximately one third of the total energy input in crop production (1). Ammonium nitrate is made either from natural gas or from the gassification of coal, both non renewable resources and the process churns out huge amounts of CO2.

The macro nutrients – phosphorus, potassium, calcium and magnesium – all are mined from non-renewable naturally occurring deposits and then processed to extract the elements. The process is also highly energy consuming but small compared with nitrogen.

Phosphate mining in Utah USA
Photo: Tillman - Phosphate mining in Utah USA

So there are distinct problems with the production & application of most fertilisers. Even the Soil Association’s organic crop production standards accept the use of mined materials to provide essential nutrients (4). The SA standards do completely rule out the use of inorganic elements and in particular ammonium nitrate.

Given the SA standards the big question is ‘Can organic systems produce the necessary yields needed to feed the world and return the farmers a profit?’ Currently the business model is to maximise yield per area cropped, and maximise the speed of turn-around – it has to be questioned if this is actually necessary, and can we accept lower yields from more land area in return for improved quality of soil structure, less energy use, less CO2 emissions?

That of course raises all sorts of questions, especially in this post Brexit world. Surely if we value our soils, nutrient reserves and aquatic life, and agree that the use of non renewable resources in the manufacture of fertilisers is unsustainable; then the public might have to step in and pay to make it happen. The trouble is that if post Brexit, UK farmers are required to operate on the world stage in a ruthless free market, then they are surely going to want to maximise everything.

This is not a good place to be.

However there is hope on the horizon. It may be that the preceding arguments might soon become increasingly archaic! With realisation of the problems we face, and with a little help it is amazing how ingenuity is being allowed to breath once more. And there are some incredible innovations in the pipeline that could revolutionise the way we produce food without plundering the planet and pumping out CO2.

One such innovation is to extend the known process of nitrogen fixation by certain bacteria (cyanobactera) in legumes, to other crops, and in doing so completely obliterate the need to apply additional nitrogen (2). This will require the dreaded genetic manipulaton – but that’s a subject for later.

Photo: Cyanobacteria. Josef Reischig/Wiki Commons

Another process now in the early stages of production is the capture of nitrogen from renewable resources such as anaerobic digestion, and combining it with carbon that has been captured from industrial processes and turning it into a pelleted product with exactly the same nitrogen content as conventional fertiliser (3).

Factory chimneys
Photo: Smoke stacks - Carbon capture should be obligatory


(1) Clark W. Gellings, Kelly E. Parmenter, (2004), ENERGY EFFICIENCY IN FERTILIZER PRODUCTION AND USE , in Efficient Use and Conservation of Energy, [Eds. Clark W. Gellings, and Kornelis Blok], in Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the UNESCO, Eolss Publishers, Oxford ,UK, [http://www.eolss.net]

(2) Washington University St Louis https://phys.org/news/2018-07-bacteria-fertilizer-thin-air.html.

More information: Deng Liu et al, Engineering Nitrogen Fixation Activity in an Oxygenic Phototroph, mBio (2018). DOI: 10.1128/mBio.01029-18

(3) Closing the Loop – making nitrogen fertiliser from waste

CCm Technologies: https://ccmtechnologies.co.uk/

(4) Soil Association Standards: https://www.soilassociation.org/media/15931/farming-and-growing-standards.pdf Pages 69 – 75.

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