Phosphate resources management

Introduction

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 ways in which dependence on mineral reserves could be reduced.

What is the role of phosphate in food production?

Phosphorus is a chemical element that is a vital nutrient for all living organisms and cannot be substituted. In modern agriculture, it is essential for maintaining the high production rate in agricultural systems. Since the 20th Century, the flow of phosphorus into the environment has quadrupled, while its use provides sufficient food to sustain high levels of population growth.

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. However, much of the phosphate consumed by the animals ends up in manure, and so remains on the farm for further production.

Is phosphate a resilient resource?

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 remaining 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. Phosphate rock was added onto the list of critical materials in may 2014.

Although reserves are expected to last for several centuries, at some point there will be a decrease in production, and this decrease in availability needs to be adressed. More effective methods of using fertilisers and ways to recover the phosphorus that is lost into the environment at all points in the chain of production need to be implemented. Recovery from waste water is already in place in many parts of the world where there are sewage treatment plants.

How is phosphate also an environmental pollutant?

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.

In aquatic environments, this excess of nutrients can cause algal blooms and reduce biodiversity, which is a process known as eutrophication, that is caused by phosphorus in rivers and lakes, but not in oceans, where it is usually caused by nitrogen.

How can phosphorus pollution be managed?

Efficient agricultural use of phosphate fertilisers and transfer from agricultural land to surface waters can be managed at three different stages:

• Managing sources: Applying the correct amount of fertilisers at the right place and at the right time ;
• Controlling how it leaves farmland: Managing surface water runoff over the tracks used by machinery in fields and establishing cover crops in autumn ;
• Protecting aquatic environments : Building artificial wetlands, silt traps and embankments, managing riverbank zones with woodland and vegetated buffer strips.

Waste water discharge from sewage treatment plants contributes 60-80% of the phosphorus in rivers, and there is a growing trend to recover it and to use it again as fertiliser.

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.

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.