Not many people recognize it, but soil DOES have an essential structure microscopically. Gardeners (especially the edible kind) like use food analogies as often as possible (because, well, we like to eat what we grow usually) and the way soil holds itself is called its "crumb." Think of the entire soil you use like a cake, and your have moist cakes, dry cakes (sandy soil) and those fudgey ones (clay soil). While we all have our preferences, typically the moist ones are preferred, or as in this case, most vegetables like a moist, well held together crumb cake that is just crumbly enough to allow drainage, but enough to hold nutrients and allow for root development.
Most complex cake you'll ever encounter hm?
To make this even more fun to comprehend, think of it as a cake HOUSE, or PLANET. Preserving good soil structure is important not only for plants but also for other biological activity such as microbes and earthworms.
Some of the best, most fertile dirt around, such as forests and woodlands, don't get messed with. Trees grow, leaves fall, animals die, things decompose, scavengers and fungi break things down and only the earthworms are dragging that stuff below.
There's no loud obnoxious bladed tiller or any animal of any sort doing that in the forests, FORCING STUFF into the ground. If things are going well, Nature is progressing along happily and healthily, the earthworms are doing the tilling for you, and in such a GENTLE manner.
Besides, tillers are expensive and more work than most people need in the size of gardens they have.
If you were an earthworm and there was an earthquake above you, you'd be scurrying away as fast as possible too. Might not even want to come back.
When tilling is involved, all the settled and comfortable organisms are exposed to an alien, inhabitable environment (even though its only some inches higher) and are subject to unfavorable conditions, stressed and can potentially die, unable to regenerate your soil or preserve its nutrient contents.
In addition, messing with your soil too heavily can increase soil compaction, bring up years old weed seeds above ground initializing them to sprout (little do many people know, many seeds need light to germinate).
(If you are concerned too about your CO2 levels, it's good to note that tilling increases CO2 release when soil is broken up (and I suppose through use of a tiller...). Instead, to aerate and "fluff" up your soil don't do more than use a garden fork to poke holes in the soil all around to allow air and water in.)
Fertilizer or compost in DOES NOT have to be dug into the ground. Regular watering will help nutrients seep into the soil or earthworms themselves will bring the nutrients and organic matter into the ground as well as produce their own "fertilizer" for you. *cough* think of them as tiny pink legless bovines. No tilling also increases earthworm population, an indicator of great soil and it is suggested to take "core" samples of your soil (you can use a shovel if you like) to get an idea of how many earthworms you have in your soil. More, the better usually. If your soil becomes less rich in organic material, the earthworms will simply move elsewhere, so... keep them happy and fed!
Not tilling also more water efficient, keeping the soil less exposed and reducing the need to weed as well as reduced erosion. This method's ability to retain water is due in part to its emphasis on the need to mulch (think tree leaves in the forest again). Mulching is easier, and less expensive than than most people realize. You don't need to go out and buy expensive stuff. Newspaper, dried out grass (or grass that has been cut and set out for at least a month because it will actually draw fertilizing nitrogen OUT from the soil rather than put it into the soil when fresh), straw (with assurances the grass seed is dead), hay, wood shavings, forest "duff" (I'm lucky, I have pine trees behind my property that provides such duff), and green mulches/cover crops are excellent mulches.
Cover crops can compromise no till somewhat as the vegetation being used as a cover crop must be turned prior to it going to seed, but it is still less damaging to the soil than deep tilling.
Proponents of the no-till method include the Rodale Institute,the great Masanobu Fukuoka and many other organic and ecological groups.
The Rodale Institute is a highly regarded organic gardening, farming, ecological group that is involved in publishing many great garden books I enjoy.
Lesser known is Masanobu Fukuoka, an originator of the "No Work" gardening method. While I am intrigued by his many methods towards natural gardening, I don't think I have enough land to grow the cereal grains he relies on to keep in his garden cycle and feel more drawn to biointensive/synergistic/permaculture gardening. I highly suggest that if you are interested to read about it on the site listed below.
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