Phosphorus: the “shortage” of an abundant mineral

Understanding where phosphates come from and how we got hooked on fertilizers

The macronutrient trio, N-P-K: nitrogen, phosphorus, and potassium are the main focus of plant fertilizers, not because our soils lack these nutrients, but because we’ve disrupted natural cycles that provide these essential minerals to plants. 

The inadvertent disruption of nutrient cycles is what prompted the development of methods, like plant fertilizer, that bypass natural processes altogether.

On one hand, man-made plant nutrients have allowed for human populations to grow abundantly with fewer immediate devastating consequences, like hunger and famine, as a result of harmful farming practices.

However, our means of bypassing natural cycles has also put us in a precarious position with long-term environmental impacts which may ultimately harm humankind (and many many other kinds) much more significantly than bouts of famine would have in the 1800’s when these industrialized methods were developed.

The time we’re living in now isn’t all bad news; it’s actually very encouraging to be in this era and here’s why: 

We have the insight and resources to be better stewards of our environment.

The story of phosphorus illustrates this. Shall we go down this rabbit hole, together? 🕳️🐇

Phosphorus mostly exists in a mineral form on Earth

We’ve talked about ✅ nitrogen (N) and ✅carbon (C). Both of which mostly exist in a gaseous state in the atmosphere before making their way into the rootzone via biological processes like photosynthesis and nitrogen-fixing microbes. 

Phosphorus (P) is different.

It’s an entirely sedimentary cycle i.e. it’s not an atmospheric gas, but rather exists mostly as a mineral, found in rocks and soil across our planet - sounds convenient, right?

The challenge with phosphorus (P) is that it’s very stable in its mineral form and not particularly eager about becoming plant food.

Plant-available P is in the form of orthophosphates H₂PO₄^- and HPO₄^2-

Phosphorus happily nests itself inside the lattice work of minerals rendering itself inaccessible for biological uptake. In soil lingo we call this an immobile nutrient.

But GET THIS:

Phosphorus has been behaving like an immobile nutrient throughout much of Earth’s history which means plants actually evolved various methods to procure this stubborn nutrient. 

Some evolved elaborate root structures to maximize exchange sites for collecting what P is available at any given time, others evolved to produce specific exudates that breakdown mineral stability thus releasing P in a plant available form, and others still developed partnerships with fungi - many of which are particularly skilled at “mining” P from minerals. 

We’re learning that arbuscular mycorrhizal fungi (AMF) specifically are essential to an estimated 70% of plants for procuring phosphorus. 🤯

Phosphorus is needed for all life on Earth

DNA, RNA, ATP ⚡, phospholipids in cell walls - all require phosphorus. It’s a key component of bones and teeth too, which store about 85% of the P in our bodies. 

The only way humans and animals uptake this essential nutrient is through the food we eat.

In short, if plants had not evolved ways to uptake phosphorus we simply wouldn’t exist.

So, you may ask, if plants have this ability, why do we find ourselves extracting phosphorus and pouring it on crop land everywhere? 🙃

To answer this, we must flip back through time to understand how we ‘got hooked on P’.

The history of using fertilizer to increase plant-available P is similar to that of nitrogen (N)

First, there was the part of human history that dates back to ancient times of using manure and other organic matter to restore fertility to land - a time without biochemical insights, but with a deep sense of knowing that soil needed to be nurtured in order to keep feeding humans.

Historically, loss of soil fertility due to mismanagement resulted in the decline of civilizations. That is, until the Industrial Revolution when the development of fertilizers hacked this cause and effect cycle, allowing us to prop plants up on dysfunctional soils without addressing underlying issues.

Remember, just as we’ve reflected on in our discussions about nitrogen, the addition of phosphates to soil only improves plant growth in degraded soils. Adding phosphates to functional soil systems doesn’t improve plant growth, in fact it disrupts natural cycles and makes plants weaker.

In 1842, shortly after German scientist, Justus Von Liebig (that guy!), discovered and popularized phosphorus (along with nitrogen and potassium) as an essential plant nutrient, an English agricultural scientist named John Bennet Lawes patented a process of treating mineral forms of P with acid, resulting in what’s called “superphosphate”. Superphosphate is water-soluble - an essential trait for plant fertilizers.

Ca₃(PO₄)₂ [rock phosphate] + 2 H₂SO₄ [sulfuric acid] → Ca(H₂PO4)₂ [monocalcium phosphate, aka “superphosphate”] + 2 CaSO₄ [gypsum]

Lawes originally demonstrated this process by dissolving bones in sulfuric acid, but this was quickly limited by the cost and availability of bone materials, which is what prompted the practice of extracting rock phosphate.

In 1843, superphosphate became the FIRST man-made fertilizer 

Today, 180 years later, the process of industrial phosphate fertilizer remains largely the same.

By the early 1900’s, agricultural scientists were beginning to understand that even though superphosphate is water-soluble and readily available to plants, once it’s applied to soils a lot of it rapidly reacts with various minerals, becoming inaccessible to plants. 🤔

How did the cultural institution of the burgeoning “ag industry” react to this insight? They told folks to apply MORE phosphorus to account for the losses of immobilized P.

The result of over applying phosphorus worldwide for generations is an abundance of phosphorus stored in soils, not a shortage

It’s estimated that for every kilogram of phosphorus that ends up in a plant, the soil may have received anywhere from 4 - 13 times as much phosphorus via fertilizers. 

Put another way, only 10 - 15% of the phosphorus we apply is actually used by plants, the rest becomes immobilized.

Economically, that is a bleak ratio - up to 90% of fertilizer purchased and handled is essentially wasted! 💸

It’s also environmentally nonsensical - the manufacturing process is energy intensive and inefficient, plus the overapplication can result in run-off, harming nearby waterways.

Interesting/Not-so-fun fact: in researching phosphorus I learned that it is the main driver of algal blooms in freshwater systems, whereas algal blooms in saltwater systems are mostly driven by excess nitrogen.

So, again, why are we still adding phosphorus to soils today?

In short, we’ve disrupted the microbiome so significantly that plants in human managed landscapes simply can’t access phosphorus. 

So… we must do something to provide plants with phosphorus. That something for the past 100+ years has been overapplying phosphorus. 

But there’s another way. 

More on that next time. 😉

Thanks so much for reading.

From my heart and soil to yours,

Andie

Have questions or concerns about phosphorus? Comment or reply to this email and I’ll try to address it in the next post!

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References:

Green Cover Seed. April 6 2021. "The Phosphorus Paradox" with Dr. Christine Jones. YouTube.

Farmers are facing a phosphorus crisis. The solution starts with soil. May 03, 2021. National Geographic. https://www.nationalgeographic.com/science/article/farmers-are-facing-a-phosphorus-crisis-the-solution-starts-with-soil#:~:text=In%201842%20an%20Oxford%20University,world's%20first%20human%2Dmade%20fertilizer. 

Phosphorus Basics: Understanding Phosphorus Forms and Their Cycling in the Soil. April 14, 2021. Alabama Cooperative Extension System. https://www.aces.edu/blog/topics/crop-production/understanding-phosphorus-forms-and-their-cycling-in-the-soil/ 

Phosphorus Behavior in Soil. July 28, 2021. Pioneer® Seeds.
https://www.pioneer.com/us/agronomy/phosphorus-soil.html

Phosphorus - Nutrient Management. n.d. Mosaic Crop Nutrition.
https://www.cropnutrition.com/nutrient-management/phosphorus 

Terry Gentry, Jeffry Fuhrmann, David Zuberer. 3^rd Edition – June 6, 2021. Principles and Applications of Soil Microbiology.