How many times have you heard the phrase petroleum based fertilizer?
I’ve heard it so many times that I’ve used the phrase myself without even questioning it,
just assuming it was correct.
But are synthetic fertilizers really petroleum based?
Are they actually made from petrochemicals?
A fertilizer buying guide in National Geographic
says “conventional fertilizers are commonly derived from petroleum”.
It even claims a 40 lb bag of fertilizer
contains the equivalent of 2 ½ gallons of gasoline.
An ad for an organic gardening product goes even further
and compares the use of synthetic fertilizers to pouring oil directly onto the soil.
This over the top comparison raised a red flag for me
and prompted me to dig deeper into this issue.
Before going further, I want to clarify that my intention here is NOT to minimize the downsides of synthetic fertilizers.
There are many.
I also don’t intend to minimize the fact that our food system is heavily dependent on fossil fuels.
Rather, I simply want to ensure that my use and advocacy of organic practices
are based on facts.
Relying on half-truths and myths to promote organic gardening
will only hurt the cause in the long run.
So, to answer the question “are synthetic fertilizers really made from petroleum”,
let’s take a look at how the N, P, and K in fertilizers are derived
and see if any of them come from petroleum.
Nitrogen in synthetic fertilizer
is harnessed from the air using the Haber-Bosch process,
which is a man-made nitrogen fixing process.
It takes atmospheric nitrogen gas, which is not bio-available,
and converts it into a bio-available form
through a reaction with hydrogen gas.
The resulting bio-available form is ammonia, or NH3.
Ammonia is then used to make a variety of other fertilizers.
So, are the nitrogen or hydrogen in NH3 derived from petroleum?
The nitrogen comes from the air, which is 78% nitrogen.
The hydrogen usually comes from methane, which is derived from natural gas.
Neither comes from petroleum.
So, it’s not accurate to say nitrogen fertilizers are petroleum based,
but it is true that the hydrogen in ammonia
comes from another fossil fuel - natural gas.
However, I would definitely NOT take it a step further and compare the use of synthetic nitrogen fertilizers
to pouring liquefied natural gas on my garden soil. It’s really nothing like that.
Even though the hydrogen comes from natural gas,
the resulting ammonia (NH3) is the same as if the hydrogen had come from a different process,
like the electrolysis of water.
Okay, let’s move on to phosphorus.
The phosphorus in synthetic fertilizers almost always comes from mined phosphorus rock,
which is the same source used in many organic fertilizers.
However, to make the phosphorus plant available,
the rock phosphate is then reacted with other chemicals like ammonia
to produce fertilizers such as diammonium and monoammonium phosphate.
These fertilizers bring together the nitrogen from the Haber-Bosch process
and the phosphorus from rock phosphate.
So, the phosphorus in synthetic fertilizers does not come from petroleum.
It comes from phosphorus rock.
What about potassium? Does it come from petroleum?
No it doesn't.
The potassium in synthetic fertilizers is mined from salts that were left behind
after the drying of ancient oceans.
So, the N, P, and K in synthetic fertilizers
don’t come from petroleum.
Nitrogen comes from the air,
phosphorus comes from phosphorus rock,
and potassium comes from the remains of ancient oceans.
However, the hydrogen in ammonia produced by the Haber-Bosch process
does typically come from another fossil fuel - natural gas.
As I mentioned earlier, my intention here is not to defend synthetic fertilizers
or minimize how dependent our food system is on fossil fuels.
I simply want to do my best to separate fact from fiction
so that when I advocate for organic gardening practices
I know I'm standing on solid ground.
In the upcoming weeks, I hope to release another video
about why I prefer organic gardening practices
over the use of synthetic fertilizers.
Well, that's all for now.
Thank you very much for watching,
and until next time remember
you can change the world one yard at a time.