For years I have added compost, horse manure and all other forms of helpful stuff, mostly to no avail. Still hard clay type soil, that by the end of the growing season, found cracks as though an earthquake hit my plots. So I tilled...and tilled...and tilled in all that helpful stuff. Addicted as I am to the process, much has been written & read by me about the evils of tilling - poor soil structure. So this year all my will power mustered, the tiller awaits in the shed. Instead I purchased a $200 (!) broadfork. So I am only turning over, with that expensive tool, the part in the row I actually have to seed. The query - in that 4 to 8" strip of area I am seeding, I am breaking up the clumps with my hands. Isn't this too ruining the soil structure? The soil has to be friable enough for seeds to germinate. So, what to do what to do.
If you have the wherwithall to work it by hand- I think you will be better off rather than worse off. The force of your hands can't be as much as power equipment. So bonds between smaller clumps will hold together.
I have not read much about this, since college, when the context was that big heavy tractors would hurt the structure in the top layers while compacting the lower layers. I don't know if they have studied home tillers that same way.
I have not tilled almost ever. My biggest improvement in structure goes along with adding organic matter. I can see my sort of sandy soil, which compacts too much, turn into clumpy more organic soil in the areas I have added the most. Your soil is likely very different from mine though.
I think there is a lot to be said for tilling up a new plot once and then top dressing after that. In urban areas, the soil tends to be very compacted and tilling can help jumpstart the process. Most of the "evils" of tilling occur when a spot is repeatedly tilled.
How are you suited for earthworms? If you can find some leaf litter and cover up your whole area, the worms will LOVE that and help move it down into the soil as it breaks up.
I had never used raised beds until I moved here to North Carolina. When I was faced with hard red clay, I knew in-ground growing of vegetables would not work because roots need to breathe. Over the past six years, I've added as much coconut coir, compost and mulched leaves as possible. I gather up worm castings from between the beds. What worms create from clay soil and leaves is remarkable! It's not quite "clay" but holds water well without being soaked. My soil is so rich, I can work it with my bare hands.
To sow seeds, I make a row with my trowel, add water, fertilizer, and seeds. Cover and leave alone. No tilling needed.
To add transplants to the garden, I dig a large hole, add water and fertilizer, set the individual transplants, pull the soil around the stems, and leave them alone.
LOTS of compost has helped my clay, but it always wnats more than I can make or afford.
You might try marking out just two square yards, and giving one yard twice as muchy compost, and the other yard three times as much compost as you usually add. See how much difference that makes.
You might also look for a mulch that breaks down slowly, like bark, especially pine bark, fir or balsam. It breaks down slowly.
Now, not everyone agrees, but I seem to see heavy clay beocme more friable (not better aearated) when I add 10-20% sand.
It mighty be better aerated if I added so much coarse grit and very fine gravel that the clay was only 20% of the whole! But who can afford that?
Instead I try to convert pure clay into poor soil in one shot by adding so much compost, shredded pine bark, and grit that the clay winds up as only 30-40% of the mix. That's expensive, since I can only make a few cubic feet of my own compost per year.
Of course, the compost is all digested in the first year, so I have to keep adding more compost than I can make or afford. And the bark breaks down after 3 or so years, so I will have to add more of that (and turn it under).
But eventually, I hope that I can get the organic matter and slow-decaying fibrous organic matter to a steady state around 20-30% , and perhaps roots and grit and soil fungus will provide another 30%. Hopefully then clumping will produce some stable clods or peds, and air will be able to get in, and water drain away.
The best success I've had so far was trying to create the fastest-draining soil I could afford for Salvia and Lavatera. I bought a yard of crushed stone (coarse grit) and a yard of medium-fine pine bark. Plus a little of my native clay that the builders were unable to b ulldoze away. The Lavatera (and maybe some pine trees) FILLED that coarse soil with roots! Whnh my new neighbor made me move that bed, I had to slice the soil into cubes instead of shoveling it. If you count the roots I had to chop, it had very permanent structure!
Soils in warm/hot climates consume organic matter is a blink of the eye and like the "little shop of horrors" screams "feed me"! I have the same problem although my soil is friable when enough moisture is present, it can and does dry out to "clay pot" status if I turn my back on it - adding sand would make the problem worse. The only salvation is organic matter added constantly, a little at a time over the growing season.
Another battle plan is to grow green manure summer cover crops such as "iron & clay" cowpeas or "red ripper" cowpeas - they have a massive root system that break up hard pan clays. Winter cover crops such as "hairy vetch" mixed with "elbon rye" and "Australian winter pea", provide abundant organic matter too. Cut these off at soil level and let the roots decompose in the soil to create air channels. Green tops can be shredded and applied as mulch or added to the compost pile.
Look into "no till" systems that rely on a layered approach, sort of a sheet composting system, and compost tea, made from non-manure compost or worm castings and supplements to "fire up" your own soil microbes which form symbiotic relationship with veggie plant roots and create that wonderful crumb-like soil texture. I also use Medina Soil Activator (Google for info) to help loosen tight soils over time.