The inoculant is more useful when you sow something "exotic", because the right bacterias are not there.
About clay soil, I suggest the japanese (i think) daikon radish that has a very long
root. It is said to be good to brake the soil and leave some organic matter deep in the soil. Cut before flowering.
Rye in your mixture will do a good job too!
If there is fennel around, it has good long
roots too.
When climate allows it, I am very fond of vetiver (does not stand frost nor shade). The roots are veeeeery long and it can stand dry and
water.
It can stop running water when the soil is too dry to suck it, and prevent erosion.
vetiver.org
It is also good mulch full of silicium.
