Iron Earth Canada

What is phosphorus?

A grape leaf shows signs of phosphorus deficiency as the foliage changes from a vibrant green to purplish-red.

Phosphorus is a chemical element that is essential for all life on earth.

What does phosphorus do for plants?

In terms of plant health, phosphorus is critical for photosynthesis and growth. If you find your plants are slow-growing or notice the foliage changing from a vibrant green to purplish-red or blue, a phosphorus deficiency may be the problem.

In a naturally occurring ecosystem, plants acquire phosphorus either from decaying organic matter (i.e., humus) or from slowly soluble rock minerals in the soil.

Most agricultural food producers, however, tend to supplement soil with phosphorus. In the past, sources such as bone meal and guano (i.e., bird droppings) were used to supplement the soil. Currently, most of the phosphorus used as fertilizer comes from mined phosphate rock. The problem, however, is that phosphate rock is a finite resource and, although it is plentiful in the earth’s crust, concentrated sources are only found in a few places in the world.

Despite phosphorus being a finite resource, over-application as an agricultural fertilizer remains a problem in North America. Too much phosphorus applied to a soil can have disastrous consequences for the environment. If an area of soil experiences any sort of erosion or run-off, phosphorus can leach into waterways and disturb natural ecosystems. Too much phosphorus in a lake, for example, can lead to the excessive growth of harmful algae. At the expense of all other aquatic life, phosphorus-fed algal blooms will utilize all of the available oxygen in a water source, thereby creating dead-zones or areas that are unsupportive of other marine life. The creation of these dead zones is called eutrophication.

How can we to add phosphorus to the soil?

A great strategy for restoring and maintaining phosphorus in our soil is to focus on humus. This advice may seem redundant, but that’s only because it is a solution for a myriad of soil issues. By adding composted organic matter to the soil, we not only prevent erosion and restore depleted phosphorus reserves, but also create an environment that fosters the growth of mycorrhizal fungi. In healthy soil, certain fungi form symbiotic relationships with plant root systems which help to increase phosphorus bioavailability and phosphorus uptake. Inoculating a soil with mycorrhizal powder may help to promote fungi growth if soil is initially lacking in these beneficial organisms.


Potassium is another element that is usually found in combination with nitrogen and phosphorus in fertilizer blends. Potassium is essential for plant life and helps to regulate turgor pressure (i.e., allows a plant to maintain its structure) as well as numerous other essential enzymatic reactions. If you find your plant leaves are looking scorched or dry and brown at the leaf tips and edges, supplementing the soil with a potassium source may help.

Like phosphorus, focusing on humus will help to restore and maintain potassium in the soil. If it is necessary to apply additional phosphorus or potassium as a fertilizer, it is best to be mindful of the amount and remember that soil health is a synergistic balance: too much or too little of a certain nutrient can disrupt the entire growth process. Adding a balanced mineral profile is best.

Renewable alternatives?

In terms of renewable mineral alternatives, certain companies are beginning to process human waste and sewage sludge in order to recover phosphorus and create fertilizers; although some may find it somewhat surprising, the recycling of human waste may prove to be an ideal alternative to mining the finite resource of phosphate rock.


Did you find this article helpful?

If so, take a look at this post where we talk more about all the macro and micronutrients in your soil!



Chang, L., Osborne, M., and Traer, M. (2016). Generation Anthropocene (Podcast). Peak Phosphorus.

Environment and Climate Change Canada (2018). Phosphorus and excess algal growth.

Functions of potassium in plants (1998). Better Crops, 82 (3)

Gardiner, D.T., and Miller, R.W. (2004). Soils in our environment, 10th Ed. New Jersey, NY: Pearson Education, Inc.
Smith, C (2016). The Naked Scientists (Podcast). Phosphorus: essential to all life, but are we running out? 

Nauta, P. 9 ways to help the beneficial fungi in your soil (blog post).