Aye i'm working on it & my current thoughts at the moment are...
Calcium carbonates alternatives - Garden lime pretty alright source of calcium carbonate/calcium oxide may contain other nutrients depending on source of rock it came from & being a PH buffer which is very easy to get hold off.
Other forms are egg shells, snail shells, marine sea shells these are all high calcium carbonate content.
Soft rock phosphate alternative - volcanic rock dust as contains pretty much just as many nutrients as soft rock phosphate also has a pretty good
CEC with a PH value between 6 & 7.
Gypsum - Found a supplyer in my own country but only deals in 25kg bags to 500 kilos but ebay has proved useful here & awaiting to put my order in.
More than likely will use biochar as it has good
CEC which the brand i'll be using is inoculated with 6 forms of mycorrhizal, worm casts & laced with kelp meal (trace macro, micro nutrients), i will also continue using bone meal as a supplement calcium source.
Compost used will be Biobizz All Mix along with some of there nutrients fish mix, alg-a-mic, bio bloom & bio heaven which fish mix & alg-a-mic can be used as a folair spray with all of these products being rated as organic & certified by OMRI/SKAL.
I like a little bit of manure tho
As humus is derived from decaying plant/organic matter aka compost & manures of a very well rotted nature which i believe is good for the microrganism population of the soil which in turn adventurely breaks down into fulvic/humic acids etc
I did have a reasonable hard time working out ratios tho which i based my calculations on metric kilo's & grams for the 6/5/3 amendment
10kg (10000g) of Biobizz All Mix compost.
Garden lime 600g
Volcanic rock dust 500g
Gypsum 300g
Bone meal, biochar, manure not included yet or at least undecided on ratio at present !
I did revisit soft rock phosphate tho about the mention of the clay particuls being good for
CEC & was wondering if that was common charactistic of all clays ?