Sustainable Phosphorus Use

Recycling waste from farming and mining could help improve the sustainable use of phosphorus, a recent study suggests. The researches traced the stocks and flows of phosphorus over a 50 year period to reveal changing patterns of global phosphorus use.

The study evaluated the past global supply, demand and depletion of phosphorus resources and modelled the global stocks and flows of phosphorus from 1961 to 2013 using data from a range of sources.

The result: Over the five decades, the amount of phosphorus extracted from phosphate rock rose by over four times, from 14.6 teragrams or 14.6 million tons of phosphorus (Tg P) in 1961 to 68.7 Tg P in 2013. Most of this increase is related to producing mineral phosphorus fertilisers. Furthermore, the study found out, that the demand for animal products increased at a higher rate than the global demand for phosphorus over the study period.

The source of agricultural phosphorus has also changed: In 1961, 29 percent of phosphorus requirements for global croplands and grasslands came from mineral fertilisers, while 56 percent was derived organically, from manures, crop residues and human excrement. By 2013, 56 percent of agricultural phosphorus inputs came from mineral fertilisers, while 38 percent came from organic sources.

The researchers suggest changes to sustainably manage phosphorus resources. A return to recycling farm organic waste would significantly improve the sustainable use of phosphorus. Careful management would be needed to ensure only sufficient phosphorus is applied and retained, so that surplus phosphorus does not pollute water through run-off, leaching or soil erosion.

Improved soil conservation practices, particularly in Europe and the United States, have already resulted in a significant reduction in phosphorus reaching the water environment. In 1961, 90 percent of global phosphorus water pollution was from agricultural land. By 2013, this source accounted for 28.5 percent of phosphorus water pollution. Waste from agricultural production increased from 9.8 Tg P in 1961 to 20.7 Tg P in 2013, although its relative contribution dropped from 45.9 percent to 28.5 percent.

Waste from mining phosphate rock contributed just 3 percent of phosphorus water pollution in 1961, and 62 percent in 2013. Mining waste was also responsible for 50 percent of phosphorus wastes from all sources in 2013. So recycling waste streams would improve the efficiency of phosphorus use, although the researchers point out that the number of impurities and low concentration of phosphorus in mining waste make its recovery more challenging.

Photo: Fraunhofer IFF