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World food security depends on the use of fertilisers, and mainly on phosphate fertilisers that are manufactured from phosphate ore, which is a limited resource. The majority of remaining reserves are found in a limited number of countries, which poses geopolitical risks. The report highlighted here describes the various uses of phosphate and summarises some ways in which dependence on mineral reserves could be reduced.
Phosphorus is a chemical element that is a vital nutrient for all living organisms. It is essential for maintaining high yields in all agricultural systems and cannot be substituted. Phosphate is a molecule containing phosphorus that is the form that is used by biological systems.
Producing the food consumed by someone who eats meat requires approximately three times as much phosphate compared to producing food for someone with a vegetarian diet, although much of the phosphate consumed by the animals ends up in manure, and so remains on the farm for further production.
Since the 20th Century, the amount of phosphorus into plants, soils and water ways has quadrupled the flow of phosphorus into the environment, while providing sufficient food to sustain high levels of population growth.
Only 10-15% of applied fertiliser is taken up by crops; the majority remains as a reserve in the soil. A large part of the phosphate extracted is lost into the environment between extraction and use in the field. This phosphate finds its way into rivers, lakes, and eventually the oceans.
Because only a fraction of the naturally-occurring organic phosphorus in the plant component of the feed can be utilised by the animal, inorganic phosphate supplements are added in feed. Of the global phosphorus supply, 5% is added to animal feed. A high proportion of the total phosphorus ends up in the manure.
The use of phosphate fertilisers intensified in the mid to late 19th century with the use of guano (mined bird and bat droppings) from islands in the Pacific. Before, bone meal was used for centuries as a source of phosphate. Since the 20th Century, the primary source of phosphate for fertiliser and animal feed supplements is phosphorus extracted from phosphate-rich rocks.
The majority of the known mineral phosphate deposits are located in North Africa (64%), the USA (15%) and China (6%). This concentration of production in a limited number of countries, and the location of some of these deposits in areas of geopolitical tension, has the potential to disrupt supply. Based on the estimated reserves, it is projected that production should peak somewhere between 2051 to 2092, but reserves should last for several centuries. This takes into account that on the one hand, demand in the future is expected to rise because of population growth and of rapidly increasing demand for meat in developing countries, which requires animal feed with high phosphorus content. On the other hand, more efficient agricultural technologies, mining and processing capabilities, rate of recycling, and further exploration should improve resiliance of the resources.
Phosphate resources need to be carefully managed because of the limited supply of high grade phosphate, a risk of political unrest in some of the supplying countries and environmental problems caused by an excess of phosphorus in waterways.
The supply of phosphate from mined deposits is limited and efficient management of phosphate to minimise losses and develop recycling would enhance the resilience of supply. However, a more efficient use of fertiliser and manures could reduce the amount of phosphate used and also environmental damages. More and more, lower-grade phosphate rocks are being used as better techniques are developped to recover the phosphate from the rocks.
It is also possible to recover phosphate from water. The concentration found in the oceans is not high enough to make recovery economically viable, but it is possible to do so with waste water. Waste water treatment and re-use as fertiliser is a growing trend.
Currently, there is no EU policy to address security of supply, such as by increasing efficiency or recycling. It is in this context that phosphate rock was added onto the EU list of critical materials in May 2014 and that the European Sustainability Phosphorus Platform (ESPP) is raising awareness of the need to tackle phosphate problems. ESPP is working to engage all relevant parties including the mining companies located in Northern Africa.
The price of phosphate rock also plays a role in its availability and is influenced by a number of factors. For example, in 2008, prices increased by 800%, due to a combinaison of factors :
Phosphate pricesfell sharply in late 2008, but the phosphate rock price has still not returned to pre-event values.
Only 10-15% of applied fertiliser is taken up by crops; the majority remains as a reserve in the soil. Aside from chemical fertiliser, phosphorus is also added to soil through animal manure and the solids from sewage treatment plants. Approximately 55% of phosphorus in food for all diets is lost between ‘farm and fork’ including waste in processing, transportation and storage.
There is disagreement in estimates of the loss of primary (mined) phosphate to the environment with figures ranging from 80% to 95% throughout the various stages of phosphorus production and use, however, much of this loss could be avoided.
In aquatic environments, an excess of nutrients can cause algal blooms and reduce biodiversity, this is a process known as eutrophication. It is usually a result of the input of the one nutrient that is ‘limiting’, that is the one that is present in a concentration low enough to limit the growth of various organisms. In lakes and rivers, this is usually phosphorus, and even if the amount of phosphorus that ends up in the environment from agricultural land, is small (1-10%), it still account for 20-30% of the phosphorus in rivers, and can create significant eutrophication problems.
Phosphate ultimately ends up in the oceans, but the eutrophication process in oceans is usually caused by an excess of nitrogen and not of phosphorus, but it can also be caused by the use of fertilisers in agriculture.
Phosphate transfer from agricultural land to surface waters can be managed at three different stages:
Waste water discharge from sewage treatment plants contributes 60-80% of the phosphorus in rivers. There are over 30 processes for recovering phosphate from waste water. In the UK, between 1995 and 2010, there has been a 50% reduction in phosphorus discharge from sewage treatment. The reduction has mainly been achieved by the chemical dosing of waste water with iron and aluminium salts in order to precipitate the phosphate, which is then returned to land in biosolid. In some European countries, there is legislative and regulatory support to encourage collaboration between those involved in phosphate removal from waste streams and its recycling to land.
Phosphate compounds used also to be a core component of laundry and dishwasher detergents, but use in laundry detergents has been restricted in 2004 and 2013 by EU regulations and further restrictions will apply to dishwasher detergent from January 2017. These restrictions only apply to domestic cleaning products; they do not include industrial detergents.
In Europe, the EU Water Framework Directive required limits to be set for a number of pollutants including reactive phosphorus (the amount of phosphorus potentially available for plants) in rivers and total phosphorus (all the dissolved and particulate forms) in lakes.
However, in many rivers and lakes, there is a lot more phosphorus than the set limit, in England for example it is the case in 45% of rivers and 74% of lakes. Consequently, the UK’s Environment Agency (EA) has identified phosphorus and the risks of eutrophication as a nationally significant water management issue.
Although the soil reservoir is not sufficient to provide the required phosphorus for maximum yields, taking this source into account when determining the amount of fertiliser required can result in reduced application rates.
Currently, any phosphate management is because of European water regulation and is focused on reducing environmental emissions of phosphate rather than recycling because of limitations in supply. Efficient management of phosphate to minimise losses and develop recycling would enhance the resilience of supply.
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