>> to dilute the proportion of clay in a heavy soil requires very large volumes of grit or other material.
I totally agree. But the scientists then seem to assume that, because it was necessary to get the results they wanted, that everyone CAN follow their advice and add 50% compost, or 50% whatever.
If you invert that and ask "what combination of materials can I make work on a TINY SCALE with repeated hand loabor every few years, I get a different conclusion than soil scientists who are speaking to big-field farmers.
>> It is seldom feasible to do this on anything but a small scale
Agreed. And I can't do it even on a small scale unless someone else does the wheel-barrowing and subsidizes some of the cost.
>> and, for most gardeners, other options such as raised beds, adding organic matter ...
Exactly. Maybe even "of course". Have they addressed the case where you are NOT adding "very large volumes of grit or other material", but only adding the amount that you can afford and transport, like 5-15%? I understand "that's not enough" to do the job all by itself.
But it's not "either-or". We don't have to choose between "50% sand right now" and "30% compost twice a year forever". 5-10% sand and grit, plus 30% compost now, plus whatever I can afford later, makes usable soil, and I can afford that.
And, in the subset of this exception to what they are mainly talking about that applies to me, I even have a hard time getting enough organic matter into the beds to do the job all by itself.
I never heard anyone address the relative merits of combining different amounts of compost, sand and grit when you can't afford 50-70% grit OR 50% compost added every year.
In that sub-sub-subset that applies to me, I've found (or I imagine) that I get better results when I add a little grit and snad to as much compost as I can afford.
And I don't think anyone would argue about adding as much compost as you can afford to any pitiful clay that had less than 50% sand and grit. At least we all agree about that.
