What is so important about Phosphorus? (1/4)

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: Here you will find clear descriptions of what you just saw, how they know what they said they knew, why they know it to be trustworthy information. Finally we will ask the question, "So what!" and explore why the information is important.

WHAT do we know?

As agroecologist Tim Crews explains in this clip from the 2009 public presentation “Agriculture After Norman Borlaug,” phosphorus (P) is an essential nutrient for life. For instance, P is one of the primary elements of DNA, which means that all known organisms -- plants, animals, and even amoebas—need phosphorus. Although humans generally get enough of it in our diets, the demand for P by plants is very high relative to the supply of it in soils. Thus, in many instances around the world, the availability of P restrains of how much can grow in a given area. For this reason, P is considered by ecologists to be a limiting nutrient.

HOW do we know?

The model presented by Dr. Crews is a qualitative depiction of the phosphorus cycle, meaning that it characterizes processes conceptually but not quantitatively. A model like this is a simplification of a much more complex system. Components of the model are derived from observations, though, due to the enormity of landscapes, inferences and generalizations must be drawn from limited observations. As a result, models are not exact replicas of the real world but rather imperfect, though useful, representations.

WHY can this be trusted?

Confidence in our basic understanding of the importance of P comes from centuries of work by biologists, biologists, chemists, and other scientists. For instance, P was first discovered to be important component of bone in 1771. Subsequently, reproducible observations have found P as an important element of every living thing. A basic premise that leads to confidence in estimates of nutrient use and release is the principle of conservation of mass, which states that matter is never lost within a system, only shifted from one state and location to another. Scientists like Dr. Crews apply this principle to the phosphorus cycle to qualitatively and quantitatively track the flow of phosphorus in and between systems within the Earth and even some inputs from space dust!


Making sense of the role of phosphorus in living systems contributes to our understanding of the natural world, which in turn furthers our understanding of managed agricultural systems. As will be explored in further clips, humans have greatly benefited from knowledge of the role of phosphorus in living systems because it has enabled us to alter phosphorus cycles in order to boost productivity, resulting in higher rates of food production. However, this has also resulted in unintended consequences, raising significant concerns about the sustainability of such practices.

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Further Reading
Further Reading: 


  • Crews, Timothy E., Kanehiro Kitayama, James H. Fownes, Ralph H. Riley, Darell A. Herbert, Dieter Muller-­‐Dombois, and Peter Vitousek. 1995. “Changes in Soil Phosphorus Fractions and Ecosystem Dynamics across a Long Chronosequence in Hawaii,” Ecology, Vol.76, No. 5 (July, 1995). Ecological Society of America, pp 1407-­‐1424. http://www.jstor.org/stable/1938144