"Till vs. No Till" certainly is a question that is hot these days. I think that there is even a thread on this forum about this but since the subject has come up here...
It is often tempting in life to latch onto an idea that seems to make sense (like no tilling) and then make the assumption that this is the ideal answer for all situations. There may be some advantages that are missed in some situations if ones actions are limited by the use of only one way of thinking about something.
I know of people who found that their vegetable production improved considerably when they finally did something mechanical to break up their soil. They chose to use a Broadfork and not a roto-tiller. There are advantages to use of a Broadfork compared to a motorized tiller (no
gasoline involved, no loud noises, no vibration, no stinky exhaust) not the least of which is the fact that the Broadfork helps facilitate soil aeration without completely disturbing the layering of the soil. By just making "slices" with the fork instead of subjecting the soil to the twirling tines of the tiller, a large proportion of the soil structuring is preserved while still benefitting from the positive effects of improved aeration.
Plant roots and favorable micro-organisms actually need oxygen and if a clay soil becomes too compressed (water droplets from the rain or from overhead watering that "crash" down onto the surface of the soil are actually the biggest offenders that contribute to clay soil compaction) then there is a risk that the roots and organisms can "sufficate" and then the plants will not be at their best.
In summary, I agree, tilling with a roto-tiller or indiscriminate plowing can be problematic--but there are some situations when mechanical activity can be helpful.
Note: I also know of a very thoughtful fellow who uses a
tractor pulled "Rotovator" to just lightly blend the top two inches of a plot for the purpose of 1) smoothing out the large soil clumps to make a more regular planting surface and/or 2) mix in cover crop or grain seeds that he has broadcast by hand. (Just leaving the seed on the surface can be a great invitation for birds to come and feast on the seed--stirring them in with a very shallow "Rotovation" is a method to keep the seed in the ground and away from the birds.)
As I understand it, even when there is an indication to perform some mechanical treatment of the soil bed, this is something that does not need to be done often--like maybe only once in the fall when putting a bed to "sleep" for the winter in prep for spring planting...
Many advocate heavy sheet mulching to cover a bed (which includes some watering) trusting that the worms will take over and churn through the mulch, breaking it down into lovely organic matter that then turns into rich humus--nice soil. Certainly this is a lovely example of
common sense soil building. Sometimes, if one wants to plant a bed densely, one has to wonder, I should think, whether a heavy sheet mulch might restrict air movement into the soil thereby potentially limiting the benefits to be had with better soil aeration ??
Back to the Nitrogen fixing idea--it seems to me that one goal is to ensure adequate organic matter in the soil that can then be acted upon by micro-organisms that will break this stuff down and turn it into valuable Nitrogen for the next round of growing to occur. Nitrogen is not always stable in the soil--too much will just leach down during the winter rainy season here in the Northwest meaning that all of the work to get the Nitrogen there in the fall may be all for naught come spring time. Timing can be important.
Other factors that would influence soil Nitrogen would be: pH, soil structure, and viability of soil micro-organisms (I'm probably missing a few things here...) all of which interact in complex ways to affect the overall Nitrogen levels in the soil and general nutrient availability. "One answer" solutions may not work in all cases due to the many complex factors that influence soils in various locations.
I understand that it is the presence of organic material in the soil in the form of slowly broken down material that can lend stability to Nutrient and Nitrogen availability. Too much soil aeration such as in a hot climate with sandy soil would result in fast combustion of organic matter meaning that it might be harder to keep the nutrient levels high enough for growing some things in this type of soil. In other cases, a soil might need help to develop enough "open" air space to facilitate the breakdown of organic matter in order to make it available for plant nutrition--is this case, perhaps mechanical action of some kind may prove to be beneficial...
What do you think??
Thanks,
Dan