Purdue Biomakers




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Phosphorus Use...and Misuse

Phosphorus is an essential nutrient for living organisms and is usually a limiting nutrient in agricultural fields. Modern farming is one of the largest contributors of phosphorus redistribution. In the past, small farms could provide the phosphorus needed for farming by recycling it from manure from animals. As commercial farming grew, livestock production concentrated into different regions from crop production. This made transferring waste back to fields inefficient energetically and economically. Thus a rise in phosphorus-heavy fertilizers began. Inorganic phosphorous is added as fertilizer where natural levels in soil cannot support crop production. The phosphorous currently used for fertilizer is mined from phosphorus reserves in the earth. The problem with these deposits include uneven distribution and increasing difficulty to access these reserves. “Some projections show economically viable mineral reserves becoming depleted within a few decades” (1). Presently, limited access to lower quality phosphorous could drive fertilizer prices higher. Food prices would in turn increase in response to the higher phosphorus prices. These higher prices would most harshly affect the ability of developing countries’ farmers who cannot accept the higher fluctuating prices of fertilizer (2).

As in farming, phosphorus is generally the limiting nutrient in freshwater aquatic ecosystems. Naturally, phosphorus is fairly scarce and is attracted to organic matter (3). When excess phosphorus is introduced into the ecosystem through farming runoff or wastewater, it disrupts the balance of chemicals and therefore the organisms present. With excess phosphorus, algal growth increases. Figure 1 shows an algal bloom in Celery Bog near Purdue University's West Lafayette, IN, USA campus. These rapidly growing blooms block out the light needed by other plants. Algae has a relatively short lifespan and die off along with the plants that can no longer get access to sunlight; this dead organic matter becomes food for decomposers to devour. The decomposers use up the majority of the dissolved oxygen depriving other organism of oxygen causing them to die (4). When these dead zones occur, the blooms can produce toxins. One such case was last summer’s 650 mile long algal bloom along the Ohio River that began to produce a neurotoxin, microcystin (5).

Figure 1: Celery Bog, near Purdue University's West Lafayette, IN, USA campus,
is covered with algae throughout the warm months of summer.

  • (1) D. L. Childers, J. Corman, M. Edwards, and J. J. Elser, “Sustainability Challenges of Phosphorus and Food: Solutions from Closing the Human Phosphorus Cycle,” BioScience, vol. 61, no. 2, pp. 117–124, 2011.
  • (2) K. Bradsher and A. Martin, “Shortages Threaten Farmers' Key Tool: Fertilizer,” The New York Times, 30-Apr-2008.
  • (4) “Algal bloom,” ScienceDaily. [Online]. Available: [Accessed: 30-May-2016].
  • (5) L. Arenschield, “Toxic algae bloom now stretches 650 miles along Ohio river,” The Columbus Dispatch, 03-Oct-2015.