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Marco Banks wrote:Yes, the initial till "lightens" the soil by introducing a lot of air into the soil profile. But it's an unnatural way of pushing that air into the soil, and it quickly compresses back to an even more compacted state because there is nothing present that holds the soil structure open. Further, all that extra oxygen artificially pumps up the microbial activity, which in turn eats up the soil carbon. Within a couple of months, you've burned through the soil carbon, leaving just mineral soil --- and that compresses like a punctured basketball.
Soil aggregation and aggregate stability are not a result of mechanical processes (running a plow through the soil) but chemical and biological processes. Well-aggregated soils are crumbly and “open”, allowing water to easily infiltrate rather than run off during heavy rain events. They will have the texture of cottage cheese. The exudates produced by plant roots are the glue that binds soil into the crumbly texture. Root surface fungi also produce aggregate glues, further enhancing aggregate stability. Without these glues, no amount of tillage will permanently "lighten" the soil because it all goes back to an even tighter formation.
The name of these fungal glues is glomalin—a chemical produced by Mycorrhizal fungi that increases microporosity (creating empty space within soil for water and air to flow through). Glomalin hangs around for about six months after the root dies and the fungi are no longer present. But it eventually breaks down, and the soil aggregates turn to powder. Every time you till, you rip those fungi to pieces, and thus hinder the production of glomalin. If you want your soil to remain aggregated, you've got to have a continual supply of glomalin being pumped into the soil ---- a living root with attached fungi, preferably, 12 months a year.
So I'd argue that its best to never till --- even the first time. If you can establish a cover crop without tilling, you'll be much better in the long run. If you can innoculate your cover crop seed with a fungal starter, all the better. But even if you don't, there are enough fungal spores floating around out there (and already present in your soil), fungi will eventually colonize your soil.
Best of luck.
Here's a link that talks about soil aggregation.
https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052820.pdf