Eat and be eaten, that is the law of nature. When Einstein defined the theory of relativity, it said space was big. Big, flat and boring. Then quantum physics came along and broke that understanding, because space on a really small level is chaotic and doesn't seem to follow the principles of Einsteins work. Needless to say the boffins are still out on this one.
On the scale of living beings here on earth we are aware of the predatory system, probably most likley because we have become the apex predotor and sit atop this ivory tower.... Much like quantum physics we are currently amused and surprised at the finding that there is a huge part of the food chain under our feet that we've never really bothered to pay attention to, except shoe it away or kill it.
Nutrient cycling in soil is an avid name to describe whats happening 6 inches under and is the result of an active microbiome, community and food chain of life. It's something that many scientists of today claim that "are just there". Well riddle me this, Batman. Since when does mother nature do something without purpose?
Nutrient cycling is actually a major part of the earh's cycles up there with nitrogen cycling and carbon cycling, we are only scratching the surface of this technology. Ironic how we're planning to head to Mars for better prospects when we haven't bothered to master what we have next to us.
Nutrient cycling is also the bit that allows us to make a very grandiose statement which is you do not need fertilizers for your farm. Mother nature can do it on her own through good active nutrient cycling.
Now you say "Wait, what? That's impossible. Everyone knows you need to feed the soil". Yes, yes you would be correct about that. But if you understand how to reframe problem statements, you'll know that this is the wrong statement connected to the wrong problem. This is the bit that I found hard to accept myself, until the science was fully explained and one with modesty should be able to admit a large piece of our current reality on earth exists for reasons of self justification over all else.
Let's look at a vivid example. We know that farmers should test their soil. Why, because how do you know what fertilizer inputs you need each year? Why waste money adding things that might harm your crop. Good farmers know absolutely that you don't just add stuff. Too much of something is definitely not a good thing. So go get your soil test done each year, or 2-3 times per year if you're a keener. Read the test or have an expert explain it to you. You need your nitrogen inpu possibly in anhydrous ammonia, or something urea based, extra potassium and phospor for your heavy feeders. Lots of calcium and magnesium in the form of dolomite. Now everything is plucky, let a good season bless us with crops aplenty, we have refilled the soil.
Wrong. Well, not wrong. Actually totally right. But again, reframe problem statement. Who said the soil was empty. The test? I'm sure a great majority of old school farmers would probably say you ain't squat if you can't rebuild your tractors combustion engine. (Nah, that's a bit too old school for even today but you get the point). Similarly, you should probably know how that test is done.
Actually this is something that plagues science in general. We can only see what we think we can test for. So we figure there's this stuff in the ground plants need, easy. We started figuring this out in the 1800s when chemistry was maturing as a science. Using a number of acids, we take some dry ground up soil and see what what we can extra from it. We then use a reagent which we know reacts with the thing we want to test for, et voilat you have pretty coloured water. We figured out how to create colour charts that show the level of something. So test your soil, let it tell you what to add. The adding part has become somewhat of an art itself.
Now go do this in the Amazon. Find a spot where you are pretty sure no human modern agriculture has touched. Test the soil. Find out it is got everything it needs in great quantities. Obviously,y because the Amazon is one of earth's lungs and the jungle is so lush and provides such gorgeous life. Again wrong.
"Ok, wth?" Nothing is there. If your agronomist returned your routine test showing you had 0.1% of anything or everything, you should literally soil your overalls on the spot. Fixing that with your local fertilizer rep would bankrupt you this season.
So this is the part where we talk a bit out nutrient availability. For the hardcore farmers who read the books, keep up to date with modern green revolution techniques should understand a few things. Any element exists in multiple forms. Only some are available to a plant. Our tests of the soil may or may not be specific about available forms of nutrients, usually the later. These things also react with each other. Each element sit across from another in terms of who gets to play in the field. Calcium and magnesium go hand in hand but you want 7:! ratio so often dolomite is a poor choice as it's relatively even and you have too much magnesium which is now pushing out your caclium availability. If you want to get into the gory details, this is actually about pH which is the hydrogen bonding sites in soil particles that allow elements to dock.
So our Amazon soil test shows up empty. The soil is dead, farmers call the insurance man its been a bad year. Not. Actually mother nature is far smarter than any of us including the agronomist and the fertilizer salesman. We've been building cars for about 50 years using Just in Time techniques. Mother nature is the OG, doing it for about 2 billion years when green plants came about.
And now we've exhuasted a few hundred words to come to the title of the article; Exudates and Nutrient Cycling. Mother nature making sure the Dutchie was passed pon de left hand side. The microbiome did the work, the nutrients were mined, processed, distributed and paid for as needed. Turns out plants don't just sit there like lumps in the ground, they talk with chemical signals in the air, water and earth all the time. Duh?
Plants photosynthesize. We all know that right? Plants convert sunlight and carbon dioxide into sugars (if you now point out that climate change is irrelevant because plants will use the co2 anyhow, I will hit you) and produce sugars in the form of carbohydrates, some proteins, etc and use it as food. We now are seeing this is only half true as plants can put half or more of these exudates into the soil, excreted through the roots.
Kegger Block party, hell yeah! Yes, this is literally true. If you left a stack of beer kegs and pizza boxes on the side of the road, you'd have a party in no time. The plant is giving is up to be the cool kid. Bacteria is coming over and getting down. The fungi hear on the mycelium-wire and is getting FOMO. Then of course the nematodes and microarthropods shows up and things get a bit nasty because they like to party rough. At some point a fat worm pops by to drop off some stash, and finally the party is busted when the police bird screeches by and everyone scatters.
Ok, silly metaphor aside this is pretty much what is going on. A symbiotic relationship lures bacteria and compounds are used to communicate a shopping list of items the plant needs. Bacteria goes out and gets it, sort of. Actually each specific population of bacteria (and we arent quite sure even how big that number is, millions or billions maybe) each get what they prefer, and sometimes other things if not available. In absence of their choice foods, they go dormant or die. The plants figured out how to call different crews to the job.
The bacteria just sit near the root system and munch away at the earth and transform unavailable to available nutrients. Sort of. It's getting complicated now. Bacteria arent' doing that at all. Their just happily eating and reproducing. Fungi are coming by eventually because they feed on bacteria, so they go where the populations are. Keeping root in the ground, and never tilling or distrubing the land allows these populations to establish. If left alone, we see fungi can grow to be hundreds of kilometers in size, creating a hyerloop trasport system of water and nutrients. Yes, Avatar is real and was based off the humungous fungus that lives in California. But we aren't getting into the reasons why you want to adopt no-till.
Nematodes, Microarthropods, Macroarthropods, are eating the bacteria, the fungi and each other. Worms eat bacteria as well, and birds each all of them. The super important part about this story is culminating right now. This is the thing that lliterally blew my mind.
We eat, we shit, we move on. Everyone does it, large to small, macroscopic to microscopic. We do this to obtain a ratio of carbon to nitrogen that is compatible with our bodies. It is not coincidental that the things we eat which are plant or animal all share a 30:1 C:N ration that we ourselves share. This makes for efficient use of energy our bodies expend in order to get the nutrients out of the food. Also not coincidental, your stomach works the same way and it is coined that soil is the stomach for plants.
Bacteria, fungi, nematodes, flaggellates, micro and macroarthropods all have differing C:N rations. It goes from predominately nitrogen and little carbon in bacteria (5:1 C/N) all the way up to trees which are mostly carbon (because their trunk mater is made of vast amounts of carbon (3000+:1 C/N) which is why we believe they are important to our envionrment as carbon stores (and why burning them is not such a good idea))
Amid the party going on in the soil, everyone is getting eaten by someone else and getting the carbon and nitrogen they need, but in uneven quantities and the predatory tree works that you always need to eat more to make up the carbon input. Thus a fungi needs to each 5 bacteria to get it's 5 units of carbon, but it only needed one unit of nitrogen, so 4 units are left over. What happens to the nitrogen, its literally pooped out and left behind. Booyah, we have nitrogen and nutrient cycling!!! The specific stuff we were talking about which bacteria have preference for is also in this exchange. The predator will use some but often not all of the nutrient content. Same way the carcass of a deer in the wild gets picked off by carrion, and then broken down to absolutely nothing by mother nature. You could describe the stock market as an overly simplified example of the trading system that goes on in the soil. Trillions are party to specific transactions with each other, some winning, some losing, all reading indicators and trying to play the game. The plant is the trading system, that actually has it's own intentions so literally each plant plays God in it's own little territory.