A while back, I sent a request to my good friend, co-conspirator in sustainable agriculture projects, source of general wisdom, and go-to agronomist, Niels Hansen. I asked Niels, “Please tell me whether there are specific reasons for favoring natural, organic-based nitrogen fertilizers over mined, synthetic, or natural gas derivative nitrogen. Synthetic is of particular interest.”

In a perfect world…

In a perfect world, I would have already known with certainty the answer to this question. I’ve studied soil science and soil chemistry. I’ve taken courses in organic gardening and organic agriculture. I know a lot about soil chemistry; enough to be completely freaked out by the fact that clay is sticky because its surface becomes intertwined with our skin at the molecular level. (EW! 😣)

And I already knew that biologically-derived fertilizers are superior to synthetically-derived versions. Fred Montag, biology professor at the University of Utah, had drilled into my brain the importance of organic content and the array of biological micronutrients necessary to a healthy soil system. More matters than just the ratios and amounts of N-P-K. But I couldn’t remember the technical, scientific reasons why.

So I went to Niels for help. Here’s what he said (lightly edited):

Plants Don’t Care

Plants don’t care as long as the molecule or mineral they need is available.

So you can look at availability. When nitrogen is spoon-fed to a plant’s roots by the local community of microbes, it can absorb it easily. When a ton is dumped on it in May, the system is taxed to accommodate all of it.

The Cheapest Fertilizer

The cheapest form of nitrogen fertilizer is ammonia, but it is so hungry to dissolve in water that it destroys all living things until it’s diluted enough to be safe. It attaches to clay particles because of its positive charge [There’s that clay thing again…] and then it becomes available to plants as the microbe community processes it into the nitrate form that plants like.

The more microbes that were killed in the initial application, the slower the ammonia is converted and made available for plants, and so the plants scavenge minerals, sugars, and amino acids from the dead microbes. That is wonderful in the short term. And it’s bad for soil health in the long term. Terrible.

Natural Gas

Haber-Bosch produced commercial nitrogen uses a LOT of natural gas to make whether it’s ammonia or ammonium nitrate. That should be an earth-stewardship consideration when looking at sustainability.

Bottom line is that it’s cheaper and environmentally positive to produce usable nitrogen with legume rotations, but that affects someone’s financial bottom line. That someone is very rich and powerful.

Mined and concentrated phosphorus

Mined phosphorus is concentrated and cheaper to move than organic forms. It is in ortho-phosphate form, which, like ammonia, has that strong positive charge so it attaches tenaciously to clay particles and negative ions in the soil. Microbes have to coax it away from the clay, but the plants are tuned into that orthophosphate molecule and have proteins that actively grab it and pull it into the roots.

In a Wild Ecosystem

In a wild, healthy soil ecosystem, it’s such a part of the living and dying process that it’s being spoon fed to plants as things die and decompose. Organic molecules very often have phosphate as a functional part of the molecule. Biochemists could get excited and wax poetic about the services and functions that involve phosphorus.

There is a lot I don’t know about all that. I can say that in a dead soil, organic phosphorus moves around a lot. In a vibrant living soil it moves around even more, sometimes even with still functioning molecules attached.

Plants Grab Sugar

Plants can grab sugar, amino acids, and other complex molecules that they can use from the soil solution. Imagine Peace Corps workers in a thrift store.

Phosphorus in manure is perfect. It’s part of the decaying plant parts there in the pile and is abundantly available for the plants to grab. It isn’t so charged up that it gets stuck in the top half inch of soil, because it’s often part of a partially functional molecule that the plant can fix up and make work.

The Trouble With Manure

The trouble is manure is bulky and is not part of a franchise with a strong advertising budget.

So there you have it: Although they feed plants just fine, synthetically-derived fertilizers don’t deliver the benefits to soils that naturally-produced fertilizers do. And where biologically-derived fertilizers contribute to a healthier soil microbiome, chemically-produced fertilizers can desolate soil microbes and leave behind a damaged or even destroyed soil ecosystem.

So go natural to the extent possible. And stay away from clay. (Just kidding. 😊)