Welsh Poultry Centre

Why the use of synthetic fertilisers is unsustainable.

What are fertilisers?

Fertilisers are the substances applied to the soil to provide the nutrients necessary to promote plant growth.

What nutrients do plants need?

The nutrient can be divided into macronutrients and micronutrients. The macronutrients are nitrogen (N), phosphorous (P) and potassium (K), with the secondary macronutrients including calcium (Ca), sulfur (S), and Magnesium (Mg). The micronutrients or trace elements include chlorine (CI), boron, (B), manganese (Mn), iron (Fe), copper (Cu), and selenium (Se).

As the names suggest the macronutrient are consumed by the plants in relatively large quantities while the micronutrients are only required in small amounts. One of the key nutrients that plants need is nitrogen.

What's the difference between organic and inorganic fertilisers?

Fertilisers can be divided into organic and inorganic sources. The organic sources include fertilisers formed from organic matter, such as farm yard manure, compost, seaweed and guano. Often included within the category are the mined fertilisers, such as rock phosphate, sodium nitrate and limestone, (these are inorganic and maybe should be termed mineral fertilisers).

Inorganic fertilisers are those fertilisers that are synthetically produced or man made. Today many farmers believe that nitrogen can only be found in synthetic or inorganic fertilisers.

Where does the nitrogen come from?

The main impact of synthetic fertilisers has been the production of nitrogen fertilisers. The manufacturing process fixes nitrogen in the form of ammonia from atmospheric nitrogen. It was first successfully done in Germany in 1909. During the First World War Germany relied on this process to produce explosives whereas the British had access to mined nitrate from Chile.

At the end of the Second World War there was a huge production capacity of synthetic nitrogen that had been built up to produce explosives. A suitable outlet for this now excess capacity was the production of nitrogen fertliser. The so-called green revolution was ironically fuelled by the production of explosives!

Since the Second World War the consumption of nitrogen fertiliser in particular has increased to over 155 million tons per year and requires 2% of the energy use of the planet to produce.

World consumption of nitrogen fertiliser (1988 figures)

(Thousands of metric tonnes)

Source FAO Fertiliser yearbook 1988

Nitrogen fertilisers account for around 72% of the total energy used to produce all fertilisers.

Of the total amount of energy roughly 72% is used to produce nitrogen fertiliser, 5% phosphate production, 3% potash production and 20% packaging, transportation and application. Soluble phosphate is produced by treating rock phosphate with an acid to produce phosphoric acid. It therefore does not require the energy of soluble nitrogen production but does use the mineral, rock phoshphate. It is estimated that at current usage this resource will be depleted within 50 years.

China now accounts for 40% of the world's consumption of synthetic nitrogen.

The figures above demonstrate an increase in usage over time. In Western Europe and North America these figures have stabilised and fallen slightly since the year 2000 due to the increasing cost of such fertilisers, (because of increasing energy costs). However, in Asia, mainly China and India, where the Governments subsidies fertilisers (in 2007 China paid $3.7 billion and India $5.3 billion in fertiliser subsidies) the figures have continued to rise. China alone now accounts for some 40% of world consumption of synthetic nitrogen.

Why synthetic fertilisers work brilliantly in the here and now

Plants need nutrients. When using organic fertilisers the micro-organism in the soil break down the organic matter, releasing the fertiliser. This is not an instant process and in some cases can actually lock up nutrients in the process of breaking down organic matter. Synthetic fertilisers dissolve when in contact with water and thus release the fertiliser molecules, which are then available to the plant. Synthetic fertilisers do not need the microbe in the soil to do this and consequently act very quickly.

Synthetic fertilisers, as they can be made with a mix of whatever nutrient suits, can be very specifically targeted at the plant needs. As fertiliser price rises due to increases in energy cost, targeting fertiliser becomes cost effective.

The rise in the use of particularly nitrogen fertilisers, coupled with advances in plant breeding and the use of herbicides and pesticides, has led to vast increases in food production. The result has been a huge increase in human population. This would not have been possible without synthetic fertilisers. As well as containing higher levels of nutrients than organic fertilisers they are easy to transport and relatively easy to apply.

Why synthetic fertilisers are unsustainable in the long term

As mentioned above the production of synthetic fertilisers is energy intensive. At present it uses something like 2% of the total world energy per year. Unfortunately this isn't the end of the story. The application of nitrogen fertiliser increases plant growth and production but it also causes the plant to be more susceptible to lodging. The lush growth also provides an excellent environment for the spread of diseases such as rust. To combat this pesticides, herbicides and insecticides need to be used. All of these are oil based and also require transporting and applying. Peak oil is estimated, depending on who you listen to, as being between 5 to 25 years away. Whenever it is, the cost of energy and therefore the cost of fertilisers is only likely to increase.

The impact of synthetic fertilisers lasts long after the crop is sold.

The use of this much fossil fuel in the production of fertilisers adds to global warming through the emission of carbon dioxide. It also adds to global warming by increasing the nitrous oxide emissions of the land fertilised by at least two times and sometimes as much as ten times the natural rate. Even if we stopped using synthetic nitrogen fertiliser today the accumulation of nitrous oxide will continue because of its long life.

Synthetic nitrogen fertiliser also adds to global warming by reducing the ability of the micro-organisms in the soil to absorb methane.

One of the advantages of synthetic fertilisers is that they dissolve in water and are therefore quickly available to the plant. If they are not used by the plant then they very quickly move out of the soil and into water systems. The result is a lot of nutrients available in the water. The name for this is eutrophication; an increase and concentration of chemical nutrients in an ecosystem to an extent that increases the primary productivity of the ecosystem.

In water this may be expressed as algal bloom, the enhanced growth of certain aquatic vegetation that chokes other plant growth reduces oxygen in the water thus affecting other life forms such as fish and shellfish. It is estimated that 53% of European lakes are eutrophic. The same process happens in coastal waters, especially estuaries.

Dependence on synthetic fertilisers leads to loss of bio-diversity

It is not just in water that biodiversity is being lost through the accumulation of chemical nutrients. The same is going on on land. Grass breeding has developed grasses which can respond well to higher applications of fertilisers. The higher levels of nutrients have driven out many of the flowering species that used to inhabit grassland. This along with the increasing use of herbicides and pesticides has seen the pollinating insects decline by a startling 80% in the last 100 years. We now have an increasing dependence on honeybees which themselves appear to be under threat.

Synthetic fertilisers encouraged the idea of feeding the plant rather than the soil. As a consequence soil organic matter has declined across all land in England and Wales (Bellamy P.H., Loveland P.J., Bradley R.I., Lark R.M. & Kirk G.J.D. (2005) Carbon losses from all soils across England and Wales 1978-2003), and indeed across the world.

Soil organic matter is all the living or decomposing dead organisms in the soil. The source of organic matter are crop residues, green and animal manures, compost and other organic matter. It is important because the organic matter in the soil is a source of food for the micro-organisms living in the soil, which thus make the nutrients available to the plants. Soil organic matter, through its decay, therefore acts as a reservoir for nutrients. It also has an ability to hold moisture in the soil and improves the structure of the soil, making root growth easier. It reduces the likelihood of soil compaction and erosion.

From a climate change point of view organic matter is of great importance as it stores carbon. It is estimated, globally, that the organic matter in soils stores three times the amount of carbon stored in vegetation. When decaying this releases CO² into the atmosphere, while being formed it removes CO² from the atmosphere.

There is another way........ clover

To put organic matter back into the soil, rotations need to be re-established instead of continual cropping and feeding the plant with synthetic fertilizers,. In this situation the nitrogen does not need to come from a bag it can come from legumes, such as clover (see article, then importance of clover). When the grass/clover ley is cultivated it is returning, not only nitrogen but also organic matter. Instead of feeding the crop we are feeding and nourishing the soil. The organic matter holds the nutrients for the plant (rather than seeing it leached into water courses) and retains moisture in the soil. The soil structure is improved, making root growth easier and improving soil structure. This in turn makes the ground less prone to compaction and erosion. Interestingly the energy required for bacteria to fix nitrogen is four times the energy taken to produce synthetic fertilizers; this all comes from the sun and not the limited amount of fossil fuels.

" There is nothing in the whole of nature which is more important than or deserves as much attention as the soil. Truly it is the soil which makes the world a friendly environment for mankind. It is the soil which nourishes and provides for the whole of nature; the whole of creation depends upon the soil which is the ultimate foundation of our existence"

Friedrich Albert Fallou, now regarded as the father of soil science, wrote these words in 1862.

When considering your farm and how poultry may fit into it consider how you use fertilisers and which fertilisers you do use. It may still be necessary to apply mineral fertilisers such as rock phosphate, which is itself a declining resource, but with correct soil testing (see article on soil testing), this can be targeted correctly. Live for today but farm as if you will live for a thousand years.

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About the author

Stephen Merritt is a partner in The Welsh Poultry Centre and an accredited advisor and board member of The Institute of Organic Training and Advice and has spent over 30 years working in sustainable agriculture in developing countries, England and Wales.  In the last 8 years Steve has specialised in free range and organic poultry production and now offers on farm advice and training to this sector.