Synthetic fertilizer is shunned by organic gardeners and one reason is the fact that they are made from petroleum, or so it is claimed. Who wants to put petroleum chemicals into their garden and then eat vegetables from them? Nobody.
Terms like oil-based fertilizer, petroleum fertilizer and petrochemical fertilizer have been used to describe synthetic fertilizers, as in this quote from a popular gardening blog, “Petrochemical fertilizers are another name for the synthetic products because they are produced using large quantities of petroleum.”
I am not going to argue for or against synthetic fertilizer in this post. I just want to examine the claim that fertilizer is made from petroleum.
What is Petroleum?
Petroleum is the same as crude oil, the material that is refined to make things like gasoline.
Unfortunately, the term is also used in a more general way to include other forms of hydrocarbon, such as natural gas and this misuse of the term leads to confusion in our discussion.
Nitrogen Fertilizer
Nitrogen is a key component of most synthetic fertilizers. It is made by combining the nitrogen in the air with hydrogen in methane to produce ammonia (NH3). The ammonia is then used to create other forms of nitrogen including ammonium nitrate and urea (ammonia + CO2).
72% of the global nitrogen fertilizer is produced using natural gas which provides the methane and a heat source for the process. 22% of the global nitrogen is produced using coal and most of this is done in China.
Petroleum, as properly defined, is not used in the majority process.
Phosphorus Fertilizer
Most of the phosphorus fertilizer is made from rock phosphate, a mineral that is mined from the ground.
Petroleum is not used in this process.
Potassium Fertilizer
Potassium fertilizer is made from mined potash, a mineral that contains potassium chloride.
Petroleum is not used in this process.
Sulfur Fertilizer
Sulfur is an important ingredient in fertilizer that is not discussed very much. Historically, there were enough impurities in fertilizer that soil received enough sulfur. Sulfur was also a component in acid rain. The manufactured fertilizer of today is purer and we have less acid rain, which is leading to sulfur deficiencies in soil.
Sulfur can be mined, but today most of it comes from refining petroleum. Sulfur is an unwanted waste product of the petroleum industry. The oil from the Canadian oil sands has high levels of sulfur and Alberta now has huge piles of it that nobody wants.
I guess you could say that sulfur is made from petroleum but we don’t use petroleum to make the sulfur. Sulfur is a waste product of other manufacturing processes, like making gasoline.
Petroleum as an Energy Source
In the above I have said several times that petroleum is not used. That is not strictly correct. Petroleum is refined to make gasoline and that is used for running all kinds of equipment. Petroleum products may also be used as a heating source.
However, every manufacturing process uses petroleum for this purpose, including all of our processed food. Even though petroleum is used to harvest and move corn to factories, and is used to heat the manufacturing process, we don’t consider cornflakes to be made from petroleum. If we did, then everything we consume would be petroleum-based, even those organic fertilizers.
You can’t make blood meal or alfalfa meal without petroleum.
Is Synthetic Fertilizer Petroleum Based?
Using the correct definition of petroleum, synthetic fertilizer containing the macronutrients N, P and K is not petroleum based.
It can be argued that sulfur is petroleum based, but the sulfur produced from petroleum or a mine is identical.
Why Does It Matter?
From a chemical perspective, it doesn’t matter. The nutrients in synthetic fertilizer are identical to those found in compost and organic fertilizer. Even if they are petroleum based, they are still identical.
Using petroleum products may not be good for the environment, but the resulting fertilizer is perfectly safe for plants, microbes and humans, provided it is used in reasonable amounts.
So why do terms like oil-based fertilizer and petroleum fertilizer exist? Proponents of organic methods need to find some way to convince people that organic fertilizer is better and labeling synthetic fertilizer as “petroleum based” easily convinces the general public that these products are BAD.
That is unfortunate, because there are very good arguments for using organic products instead of synthetic products, in some gardening situations. But trying to explain the concept of building soil structure and increasing levels of organic matter are more complex and require more knowledge of both the writer and the audience. It is so much easier to use name calling. The term, petroleum-based fertilizer, is easier to understand and more convincing.
But it’s a myth – synthetic fertilizer is NOT petroleum based.
Oft times that smell is sulfur or a biproduct of where and how they source the soil. Soil that comes from bogs is usually the cheapest available and it’s considered “responsible sourcing” is what “they” say because it comes from swamps where removing dirt there leaves less effect on the environment.
Although “synthetic” (aka “chemical”, “petroleum based”) fertilizers are the same as the end result of what enters the plant from “organic” fertilizers, all is not the same. Organics generally must be broken down by soil microbes before plants can use the nutrients. Microbes respond to heat and moisture. So do plants. So usable nutrients from organics “bleed” into the soil more in synch with plant growth.
On a practical side, organics allows for a one-time application rather than multiple applications often needed by synthetics to avoid salt-burn of roots. Also less chance of loss of soluble nutrients and subsequent contamination of groundwaters.
The best organic fertilizers — compost (although too low in nutrients to be legally classified as a “fertilizer”), for example — add bulk to the soil, providing many physical and biological benefits. Better aeration and water-holding capacity, and nourishment of microorganisms, for example. Not only do synthetics not provide these benefits but adding synthetic nitrogen fertilizer, can actually unduly speed burning up of soil carbon.
Re: Jeane’s comment – I’ve also noticed a very unpleasant smell vaguely like gasoline or asphalt or possibly sewerage sludge in potting mix, and would like to know what it is. (they were cheap, bagged mix, several brands, in Australia, no useful info on the labels)
I’ve seem some carbon footprint studies for common commodity crops, and fertilizer is typically a big component, especially the natural gas used in producing nitrogen fertilizers. But the flip side is that without this so-called synthetic nitrogen, the earth’s carrying capacity would decline by a few billion humans. So let’s use the fertilizer efficiently. A home garden also saves energy in other ways, too.
Terrific of you to offer such trustworthy information for semi-ignorant gardeners like myself.
Robert, you answer the most interesting questions. You are such an incredible source for great information. Thank you so much!
Thank you for all this information as I find it helpful. I use synthetic fertilizer in my aquariums and water gardens because I read that too many organics can cause algae and other problems and it seem true so far as I have seen.
There is no difference between synthetic and organic. If you add too much of either you get algae
Thank you! That is good to know.
Due to the current initiatives to combat climate change an alternative (though still not economically competitive process) is to make “green hydrogen” by electrolysis of water and then react that hydrogen with nitrogen to create ammonia fertiliser (NH3) via the usual Haber Process. Ammonia is also further converted into ammonium salts, nitrates, urea, etc used by home gardeners. That process cuts out the carbon middleman – natural gas (ie methane – CH4). Hopefully this becomes economically viable in the future.
However currently the hydrogen is still most economically made from methane found in either natural gas (associated or otherwise) or coal seam gas, or it has also historically been manufactured from either coal or carbon monoxide. But methane is methane no matter how it’s found or made – however note that these processes probably have differing environmental impacts.
Good post, but remember, we’re dealing with people who will hear that synthetic ferts are petroleum-based, believe it and start railing against them, while never bothering to read the ingredients label of their horticultural oil bottle (except where it says, “For Organic Gardening”).
I was really interested to read this post because one time I bought several bags of potting soil from a big box store to add my raised beds. The soil had a distinct smell very like gasoline, and also precautions in the instructions to wear gloves. I didn’t feel comfortable adding that to my vegetable garden. Not sure why the bagged soil had that strong chemical odor- nothing I saw listed on the ingredients clued me in.
Another great, informative article thanks!